The lofty towns of the plateau have a really wretched climate. White men
cannot live comfortably at Antabamba and Salamanca. Further, they are so
isolated that the modest comforts and the smallest luxuries of
civilization are very expensive. To pay for them requires a profitable
industry managed on a large scale and there is no such industry in the
higher valleys. The white who goes there must be satisfied to live like
an Indian. The result is easy to forecast. Outside of government
officers, only the dissolute or unsuccessful whites live in the worst
towns, like Salamanca and Antabamba. A larger valley with a slightly
milder climate and more accessible situation, like Chuquibamba, will
draw a still better grade of white citizen and in the largest of
all--Cuzco and the Titicaca basin--we find normal whites in larger
numbers, though they nowhere live in such high ratios to the Indian as
on the coast and in the lower valleys near the coast. With few
exceptions the white population of Peru is distributed in response to
favorable combinations of climate, soil, accessibility, and general
opportunities to secure a living without extreme sacrifice.
These facts are stated in a simple way, for I wish to emphasize the
statement that the Indian population responds to quite other stimuli.
Most of the luxuries and comforts of the whites mean nothing to the
Indian. The machine-made woolens of the importers will probably never
displace his homespun llama-wool clothing. His implements are few in
number and simple in form. His tastes in food are satisfied by the few
products of his fields and his mountain flocks. Thus he has lived for
centuries and is quite content to live today. Only coca and brandy tempt
him to engage in commerce, to toil now and then in the hot valleys, and
to strive for more than the bare necessities of life. Therefore it
matters very little to him if his home town is isolated, or the
resources support but a small group of people. He is so accustomed to a
solitary existence in his ramblings with his flocks that a village of
fifty houses offers social enjoyments of a high order. Where a white
perishes for lack of society the Indian finds himself contented.
Finally, he is not subject to the white man’s exploitation when he lives
in remote places. The pastures are extensive and free. The high valley
lands are apportioned by the alcalde according to ancient custom. His
life is unrestricted by anything but the common law and he need have no
care for the morrow, for the seasons here are almost as fixed as the
stars.
Thus we have a sort of segregation of whites in the lower places where a
modern type of life is maintained and of Indians in the higher places
where they enjoy advantages that do not appeal to the whites. Above
8,000 feet the density of the white population bears a close inverse
proportion to the altitude, excepting in the case of the largest valleys
whose size brings together such numbers as to tempt the commercial and
exploiting whites to live in them. Furthermore, we should find that high
altitude, limited size, and greater isolation are everywhere closely
related to increasing immorality or decreasing character among the
whites. So to the low Indian population there is thus added the lowest
of the white population. Moreover, because it yields the largest
returns, the chief business of these whites is the sale of coca and
brandy and the downright active debauchery of the Indian. This is all
the easier for them because the isolated Indian, like the average
isolated white, has only a low and provincial standard of morality and
gets no help from such stimulation as numbers usually excite.
For example, the Anta basin at harvest time is one of the fairest sights
in Peru. Sturdy laborers are working diligently. Their faces are bright
and happy, their skin clear, their manner eager and animated. They sing
at their work or gather about their mild _chicha_ and drink to the
patron saints of the harvest. The huts are filled with robust children;
all the yards are turned into threshing floors; and from the stubbly
hillslopes the shepherd blows shrill notes upon his barley reeds and
bamboo flute. There is drinking but there is little disorder and there
is always a sober remnant that exercises a restraining influence upon
the group.
In the most remote places of all one may find mountain groups of a high
order of morality unaffected by the white man or actually shunning him.
Clear-eyed, thick-limbed, independent, a fine, sturdy type of man this
highland shepherd may be. But in the town he succumbs to the temptation
of drink. Some writers have tried to make him out a superior to the
plains and low valley type. He is not that. The well-regulated groups of
the lower elevations are far superior intellectually and morally in
spite of the fact that the poorly regulated groups may fall below the
highland dweller in morality. The coca-chewing highlander is a clod.
Surely, as a whole, the mixed breed of the coastal valleys is a far
worthier type, save in a few cases where a Chinese or negroid element or
both have led to local inferiority. And surely, also, that is the worst
combination which results in adding the viciousness of the inferior or
debased white to the stupidity of the highland Indian. It is here that
the effects of geography are most apparent. If the white is tempted in
large numbers because of exceptional position or resources, as at La
Paz, the rule of altitude may have an exception. And other exceptions
there are not due to physical causes, for character is practically never
a question of geography alone. There is the spiritual factor that may
illumine a strong character and through his agency turn a weak community
into a powerful one, or hold a weakened group steadfast against the
forces of disintegration. Exceptions arise from this and other causes
and yet with them all in mind the geographic factor seems predominant in
the types illustrated herewith.[17]
CHAPTER VIII
THE COASTAL DESERT
To the wayfarer from the bleak mountains the warm green valleys of the
coastal desert of Peru seem like the climax of scenic beauty. The
streams are intrenched from 2,000 to 4,000 feet, and the valley walls in
some places drop 500 feet by sheer descents from one level to another.
The cultivated fields on the valley floors look like sunken gardens and
now and then one may catch the distant glint of sunlight on water. The
broad white path that winds through vineyards and cotton-fields, follows
the foot of a cliff, or fills the whole breadth of a gorge is the
waste-strewn, half-dry channel of the river. In some places almost the
whole floor is cultivated from one valley wall to the other. In other
places the fields are restricted to narrow bands between the river and
the impending cliffs of a narrow canyon. Where tributaries enter from
the desert there may be huge banks of mud or broad triangular fans
covered with raw, infertile earth. The picture is generally touched with
color--a yellow, haze-covered horizon on the bare desert above, brown
lava flows suspended on the brink of the valley, gray-brown cliffs, and
greens ranging from the dull shade of algarrobo, olive and fig trees, to
the bright shade of freshly irrigated alfalfa pastures.
After several months’ work on the cold highlands, where we rode almost
daily into hailstorms or wearisome gales, we came at length to the
border of the valley country. It will always seem to me that the weather
and the sky conspired that afternoon to reward us for the months of toil
that lay behind. And certainly there could be no happier place to
receive the reward than on the brink of the lava plateau above
Chuquibamba. There was promise of an extraordinary view in the growing
beauty of the sky, and we hurried our tired beasts forward so that the
valley below might also be included in the picture. The head of the
Majes Valley is a vast hollow bordered by cliffs hundreds of feet high,
and we reached the rim of it only a few minutes before sunset.
[Illustration: FIG. 63--The deep fertile Majes Valley below Cantas.
Compare with Fig. 6 showing the Chili Valley at Arequipa.]
[Illustration: FIG. 64--The Majes Valley, desert coast, western Peru.
The lighter patches on the valley floor are the gravel beds of the river
at high water. Much of the alluvial land is still uncleared.]
I remember that we halted beside a great wooden cross and that our
guide, dismounting, walked up to the foot of it and kissed and embraced
it after the custom of the mountain folk when they reach the head of a
steep “cuesta.” Also that the trail seemed to drop off like a stairway,
which indeed it was.[18] Everything else about me was completely
overshadowed by snowy mountains, colored sky, and golden-yellow desert.
One could almost forget the dark clouds that gather around the great
mass of Coropuna and the bitter winds that creep down from its glaciers
at night--it seemed so friendly and noble. Behind it lay bulky masses of
rose-tinted clouds. We had admired their gay colors only a few minutes,
when the sun dropped behind the crest of the Coast Range and the last of
the sunlight played upon the sky. It fell with such marvelously swift
changes of color upon the outermost zone of clouds as these were shifted
with the wind that the eye had scarcely time to comprehend a tint before
it was gone and one more beautiful still had taken its place. The
reflected sunlight lay warm and soft upon the white peaks of Coropuna,
and a little later the Alpine glow came out delicately clear.
When we turned from this brilliant scene to the deep valley, we found
that it had already become so dark that its greens had turned to black,
and the valley walls, now in deep shadow, had lost half their splendor.
The color had not left the sky before the lights of Chuquibamba began to
show, and candles twinkled from the doors of a group of huts close under
the cliff. We were not long in starting the descent. Here at last were
friendly habitations and happy people. I had worked for six weeks
between 12,000 and 17,000 feet, constantly ill from mountain sickness,
and it was with no regret that I at last left the plateau and got down
to comfortable altitudes. It seemed good news when the guide told me
that there were mosquitoes in the marshes of Camaná. Any low, hot land
would have seemed like a health resort. I had been in the high country
so long that, like the Bolivian mining engineer, I wanted to get down
not only to sea level, but below it!
[Illustration: FIG. 65--Regional diagram to show the physical relations
in the coastal desert of Peru. For location, see Fig. 20.]
If the reader will examine Figs. 65 and 66, and the photographs that
accompany them, he may gain an idea of the more important features of
the coastal region. We have already described, in Chapters V and VII,
the character of the plateau region and its people. Therefore, we need
say little in this place of the part of the Maritime Cordillera that is
included in the figure. Its unpopulated rim (see p. 54), the
semi-nomadic herdsmen and shepherds from Chuquibamba that scour its
pastures in the moist vales about Coropuna, and the gnarled and stunted
trees at 13,000 feet (3,960 m.) which partly supply Chuquibamba with
firewood, are its most important features. A few groups of huts just
under the snowline are inhabited for only a part of the year. The
delightful valleys are too near and tempting. Even a plateau Indian
responds to the call of a dry valley, however he may shun the moist,
warm valleys on the eastern border of the Cordillera.
[Illustration: FIG. 66--Irrigated and irrigable land of the coastal belt
of Peru. The map exhibits in a striking manner how small a part of the
whole Pacific slope is available for cultivation. Pasture grows over all
but the steepest and the highest portions of the Cordillera to the right
of (above) the dotted line. Another belt of pasture too narrow to show
on the map, grows in the fog belt on the seaward slopes of the Coast
Range. Scale, 170 miles to the inch.]
The greater part of the coastal region is occupied by the desert. Its
outer border is the low, dry, gentle, eastward-facing slope of the Coast
Range. Its inner border is the foot of the steep descent that marks the
edge of the lava plateau. This descent is a fairly well-marked line,
here and there broken by a venturesome lava flow that extends far out
from the main plateau. Within these definite borders the desert extends
continuously northwestward for hundreds of miles along the coast of Peru
from far beyond the Chilean frontier almost to the border of Ecuador. It
is broken up by deep transverse valleys and canyons into so-called
“pampas,” each of which has a separate name; thus west of Arequipa
between the Vitor and Majes valleys are the “Pampa de Vitor” and the
“Pampa de Sihuas,” and south of the Vitor is the “Pampa de Islay.”
The pampa surfaces are inclined in general toward the sea. They were
built up to their present level chiefly by mountain streams before the
present deep valleys were cut, that is to say, when the land was more
than a half-mile lower. Some of their material is wind-blown and on the
walls of the valleys are alternating belts of wind-blown and water-laid
strata from one hundred to four hundred feet thick as if in past ages
long dry and long wet periods had succeeded each other. The wind has
blown sand and dust from the desert down into the valleys, but its chief
work has been to drive the lighter desert waste up partly into the
mountains and along their margins, partly so high as to carry it into
the realm of the lofty terrestrial winds, whence it falls upon surfaces
far distant from the fields of origin. There are left behind the heavier
sand which the wind rolls along on the surfaces and builds into
crescentic dunes called médanos, and the pebbles that it can sandpaper
but cannot remove bodily. Thus there are belts of dunes, belts of
irregular sand drifts, and belts of true desert “pavement” (a residual
mantle of faceted pebbles and irregular stones).
[Illustration: THE YALE PERUVIAN EXPEDITION OF 1911
HIRAM BINGHAM, DIRECTOR
CAMANÁ QUADRANGLE
(_Aplao_)]
Yet another feature of the desert pampa are the “dry” valleys that join
the through-flowing streams at irregular intervals, as shown in the
accompanying regional diagram. If one follow a dry valley to its head
he will find there a set of broad and shallow tributaries. Sand drifts
may clog them and appear to indicate that water no longer flows through
them. They are often referred to by unscientific travelers as evidences
of a recent change of climate. I had once the unusual opportunity (in
the mountains of Chile) of seeing freshly fallen snow melted rapidly and
thus turned suddenly into the streams. In 1911 this happened also at San
Pedro de Atacama, northern Chile, right in the desert at 8,000 feet
(2,440 m.) elevation, and in both places the dry, sand-choked valleys
were cleaned out and definite channels reëstablished. From a large
number of facts like these we know that the dry valleys represent the
work of the infrequent rains. No desert is absolutely rainless, although
until recently it was the fashion to say so. Naturally the wind, which
works incessantly, partly offsets the work of the water. Yet the wind
can make but little impression upon the general outlines of the dry
valleys. They remain under the dominance of the irregular rains. These
come sometimes at intervals of three or four years, again at intervals
of ten to fifteen years, and some parts of the desert have probably been
rainless for a hundred years. Some specific cases are discussed in the
chapter on Climate.
The large valleys of the desert zone have been cut by snow-fed streams
and then partly filled again so that deep waste lies on their floors and
abuts with remarkable sharpness against the bordering cliffs (Fig. 155).
Extensive flats are thus available for easy cultivation, and the
through-flowing streams furnish abundant water to the irrigating canals.
The alluvial floor begins almost at the foot of the steep western slope
of the lava plateau, but it is there stony and coarse--hence
Chuquibamba, or plain of stones (chuqui = stone; bamba = plain). Farther
down and about half-way between Chuquibamba and Aplao (Camaná
Quadrangle) it is partly covered with fresh mud and sand flows from the
bordering valley walls and the stream is intrenched two hundred feet. A
few miles above Aplao the stream emerges from its narrow gorge and
thenceforth flows on the surface of the alluvium right to the sea.
Narrow places occur between Cantas and Aplao, where there is a
projection of old and hard quartzitic rock, and again above Camaná,
where the stream cuts straight across the granite axis of the Coast
Range. Elsewhere the rock is either a softer sandstone or still
unindurated sands and gravels, as at the top of the desert series of
strata that are exposed on the valley wall. The changing width of the
valley is thus a reflection of the changing hardness of the rock.
There is a wide range of products between Chuquibamba at 10,000 feet
(3,050 m.) at the head of the valley and Camaná near the valley mouth.
At the higher levels fruit will not grow--only alfalfa, potatoes, and
barley. A thousand feet below Chuquibamba fruit trees appear. Then
follows a barren stretch where there are mud flows and where the river
is intrenched. Below this there is a wonderful change in climate and
products. The elevation falls off 4,000 feet and the first cultivated
patches below the middle unfavorable section are covered with grape
vines. Here at 3,000 feet (900 m.) elevation above the sea begin the
famous vineyards of the Majes Valley, which support a wine industry that
dates back to the sixteenth century. Some of the huge buried earthenware
jars for curing the wine at Hacienda Cantas were made in the reign of
Philip II.
The people of Aplao and Camaná are among the most hospitable and
energetic in Peru, as if these qualities were but the reflection of the
bounty of nature. Nowhere could I see evidences of crowding or of the
degeneracy or poverty that is so often associated with desert people.
Water is always plentiful; sometimes indeed too plentiful, for floods
and changes in the bed of the river are responsible for the loss of a
good deal of land. This abundance of water means that both the small and
the large landowners receive enough. There are none of the troublesome
official regulations, as in the poorer valleys with their inevitable
favoritism or downright graft. Yet even here the valley is not fully
occupied; at many places more land could be put under cultivation. The
Belaunde brothers at Cantas have illustrated this in their new cotton
plantation, where clearings and new canals have turned into cultivated
fields tracts long covered with brush.
The Majes Valley sorely lacks an adequate port. Its cotton, sugar, and
wine must now be shipped to Camaná and thence to Mollendo, either by a
small bi-weekly boat, or by pack-train over the coast trail to Quilca,
where ocean steamers call. This is so roundabout a way that the planters
of the mid-valley section and the farmers of the valley head now export
their products over the desert trail from Cantas to Vitor on the
Mollendo-Arequipa railroad, whence they can be sent either to the cotton
mills or the stores of Arequipa, the chief distributing market of
southern Peru, or to the ocean port.
The foreshore at Camaná is low and marshy where the salt water covers
the outer edge of the delta. In the hollow between two headlands a broad
alluvial plain has been formed, through which the shallow river now
discharges. Hence the natural indentation has been filled up and the
river shoaled. To these disadvantages must be added a third, the
shoaling of the sea bottom, which compels ships to anchor far off shore.
Such shoals are so rare on this dry and almost riverless coast as to be
a menace to navigation. The steamer _Tucapelle_, like all west-coast
boats, was sailing close to the unlighted shore on a very dark night in
April, 1911, when the usual fog came on. She struck the reef just off
Camaná. Half of her passengers perished in trying to get through the
tremendous surf that broke over the bar. The most practicable scheme for
the development of the port would seem to be a floating dock and tower
anchored out of reach of the surf, and connected by cable with a railway
on shore. Harbor works would be extraordinarily expensive. The valley
can support only a modest project.
The relations of Fig. 65, representing the Camaná-Vitor region, are
typical of southern Peru, with one exception. In a few valleys the
streams are so small that but little water is ever found beyond the foot
of the mountains, as at Moquegua. In the Chili Valley is Arequipa (8,000
feet), right at the foot of the big cones of the Maritime Cordillera
(see Fig. 6). The green valley floor narrows rapidly and cultivation
disappears but a few miles below the town. Outside the big valleys
cultivation is limited to the best spots along the foot of the Coast
Range, where tiny streams or small springs derive water from the zone of
clouds and fogs on the seaward slopes of the Coast Range. Here and there
are olive groves, a vegetable garden, or a narrow alfalfa meadow,
watered by uncertain springs that issue below the hollows of the
bordering mountains.
[Illustration: FIG. 67--Irrigated and irrigable land in the Ica Valley
of the coastal desert of Peru.]
[Illustration: FIG. 68--The projected canal to convey water from the
Atlantic slope to the Pacific slope of the Maritime Cordillera.[19]]
In central and northern Peru the coastal region has aspects quite
different from those about Camaná. At some places, for example north of
Cerro Azul, the main spurs of the Cordillera extend down to the shore.
There is neither a low Coast Range nor a broad desert pampa. In such
places flat land is found only on the alluvial fans and deltas. Lima and
Callao are typical. Fig. 66, compiled from Adams’s reports on the water
resources of the coastal region of Peru, shows this distinctive feature
of the central region. Beyond Salaverry extends the northern region,
where nearly all the irrigated land is found some distance back from the
shore. The farther north we go the more marked is this feature, because
the coastal belt widens. Catacaos is several miles from the sea, and
Piura is an interior place. At the extreme north, where the rains begin,
as at Tumbez, the cultivated land once more extends to the coast.
[Illustration: FIG. 69--A stream of the intermittent type in the coastal
desert of Peru. Depth of water in the Puira River at Puira, 1905. (Bol.
de Minas del Perú, 1906, No. 45, p. 2.)]
[Illustration: FIG. 70--A stream of the perennial type in the coastal
desert of Peru. Depth of water in the Chira River at Sullana, 1905. Data
from May to September are approximate. (Bol. de Minas del Perú, 1906,
No. 45, p. 2.)]
These three regions contain all the fertile coastal valleys of Peru. The
larger ones are impressive--with cities, railways, ports, and land in a
high state of cultivation. But they are after all only a few hundred
square miles in extent. They contain less than a quarter of the people.
The whole Pacific slope from the crest of the Cordillera has about
15,000 square miles (38,850 sq. km.), and of this only three per cent is
irrigated valley land, as shown in Fig. 66. Moreover, only a small
additional amount may be irrigated, perhaps one half of one per cent.
Even this amount may be added not only by a better use of the water but
also by the diversion of streams and lakes from the Atlantic to the
Pacific. Figs. 67 and 68 represent such a project, in which it is
proposed to carry the water of Lake Choclococha through a canal and
tunnel under the continental divide and so to the head of the Ica
Valley. A little irrigation can be and is carried on by the use of well
water, but this will never be an important source because of the great
depth to the ground water, and the fact that it, too, depends ultimately
upon the limited rains.
The inequality of opportunity in the various valleys of the coastal
region depends in large part also upon inequality of river discharge.
This is dependent chiefly upon the sources of the streams, whether in
snowy peaks of the main Cordillera with fairly constant run-off, or in
the western spurs where summer rains bring periodic high water. A third
type has high water during the time of greatest snow melting, combined
with summer rains, and to this class belongs the Majes Valley with its
sources in the snow-cap of Coropuna. The other two types are illustrated
by the accompanying diagrams for Puira and Chira, the former
intermittent in flow, the latter fairly constant.[20]
[Illustration: THE YALE PERUVIAN EXPEDITION OF 1911
HIRAM BINGHAM DIRECTOR
APLAO QUADRANGLE]
CHAPTER IX
CLIMATOLOGY OF THE PERUVIAN ANDES
CLIMATIC BELTS
The noble proportions of the Peruvian Andes and their position in
tropical latitudes have given them climatic conditions of great
diversity. Moreover, their great breadth and continuously lofty summits
have distributed the various climatic types over spaces sufficiently
ample to affect large and important groups of people. When we add to
this the fact that the topographic types developed on a large scale are
distributed at varying elevations, and that upon them depend to a large
degree the chief characteristics of the soil, another great factor in
human distribution, we are prepared to see that the Peruvian Andes
afford some striking illustrations of combined climatic and topographic
control over man.
The topographic features in their relations to the people have been
discussed in preceding chapters. We shall now examine the corresponding
effects of climate. It goes without saying that the topographic and
climatic controls cannot and need not be kept rigidly apart. Yet it
seems desirable, for all their natural interdependence, to give them
separate treatment, since the physical laws upon which their
explanations depend are of course entirely distinct. Further, there is
an independent group of human responses to detailed climatic features
that have little or no connection with either topography or soil.
The chief climatic belts of Peru run roughly from north to south in the
direction of the main features of the topography. Between 13° and 18°
S., however, the Andes run from northwest to southeast, and in short
stretches nearly west-east, with the result that the climatic belts
likewise trend westward, a condition well illustrated on the
seventy-third meridian. Here are developed important climatic features
not found elsewhere in Peru. The trade winds are greatly modified in
direction and effects; the northward-trending valleys, so deep as to be
secluded from the trades, have floors that are nearly if not quite arid;
a restricted coastal region enjoys a heavier rainfall; and the snowline
is much more strongly canted from west to east than anywhere else in the
long belt of mountains from Patagonia to Venezuela. These exceptional
features depend, however, upon precisely the same physical laws as the
normal climatic features of the Peruvian Andes. They can, therefore, be
more easily understood after attention has been given to the larger
aspects of the climatic problem of which they form a part.
The critical relations of trade winds, lofty mountains, and ocean
currents that give distinction to Peruvian climate are shown in Figs. 71
to 73. From them and Fig. 74 it is clear that the two sides of the
Peruvian mountains are in sharp contrast climatically. The eastern
slopes have almost daily rains, even in the dry season, and are clothed
with forest. The western leeward slopes are so dry that at 8,000 feet
even the most drought-resisting grasses stop--only low shrubs live below
this level, and over large areas there is no vegetation whatever. An
exception is the Coast Range, not shown on these small maps, but
exhibited in the succeeding diagram. These have moderate rains on their
seaward (westerly) slopes during some years and grass and shrubby
vegetation grow between the arid coastal terraces below them and the
parched desert above. The greatest variety of climate is enjoyed by the
mountain zone. Its deeper valleys and basins descend to tropical levels;
its higher ranges and peaks are snow-covered. Between are the climates
of half the world compressed, it may be, between 6,000 and 15,000 feet
of elevation and with extremes only a day’s journey apart.
[Illustration: FIG. 71--The three chief topographic regions of Peru.]
[Illustration: FIG. 72--The wind belts of Peru and ocean currents of
adjacent waters.]
[Illustration: FIG. 73--The climatic belts of Peru.]
[Illustration: FIG. 74--Belts of vegetation in Peru.]
In the explanation of these contrasts we have to deal with relatively
simple facts and principles; but the reader who is interested chiefly in
the human aspects of the region should turn to p. 138 where the effects
of the climate on man are set forth. The ascending trades on the eastern
slopes pass successively into atmospheric levels of diminishing
pressure; hence they expand, deriving the required energy for expansion
from the heat of the air itself. The air thereby cooled has a lower
capacity for the retention of water vapor, a function of its
temperature; the colder the air the less water vapor it can take up. As
long as the actual amount of water vapor in the air is less than that
which the air can hold, no rain falls. But the cooling process tends
constantly to bring the warm, moist, ascending air currents to the limit
of their capacity for water vapor by diminishing the temperature.
Eventually the air is saturated and if the capacity diminishes still
further through diminishing temperature some of the water vapor must be
condensed from a gaseous to a liquid form and be dropped as rain.
The air currents that rise thousands of feet per day on the eastern
slopes of the Andes pass again and again through this practically
continuous process and the eastern aspect of the mountains is kept
rain-soaked the whole year round. For the trades here have only the
rarest reversals. Generally they blow from the east day after day and
repeat a fixed or average type of weather peculiar to that part of the
tropics under their steady domination. During the southern summer, when
the day-time temperature contrasts between mountains and plains are
strongest, the force of the trade wind is greatly increased and likewise
the rapidity of the rain-making processes. Hence there is a distinct
seasonal difference in the rainfall--what we call, for want of a better
name, a “wet” and a “dry” season.
On the western or seaward slopes of the Peruvian Andes the trade winds
descend, and the process of rain-making is reversed to one of
rain-taking. The descending air currents are compressed as they reach
lower levels where there are progressively higher atmospheric pressures.
The energy expended in the process is expressed in the air as heat,
whence the descending air gains steadily in temperature and capacity for
water vapor, and therefore is a drying wind. Thus the leeward, western
slopes of the mountains receive little rain and the lowlands on that
side are desert.
THE CLIMATE OF THE COAST
A series of narrow but pronounced climatic zones coincide with the
topographic subdivisions of the western slope of the country between the
crest of the Maritime Cordillera and the Pacific Ocean. This belted
arrangement is diagrammatically shown in Fig. 75. From the zone of lofty
mountains with a well-marked summer rainy season descent is made by
lower slopes with successively less and less precipitation to the desert
strip, where rain is only known at irregular intervals of many years’
duration. Beyond lies the seaward slope of the Coast Range, more or less
constantly enveloped in fog and receiving actual rain every few years,
and below it is the very narrow band of dry coastal terraces.
[Illustration: FIG. 75--Topographic and climatic provinces in the
coastal region of Peru. The broadest division, into the zones of regular
annual rains and of irregular rains, occurs approximately at 8,000 feet
but is locally variable. To the traveler it is always clearly defined by
the change in architecture, particularly of the house roofs. Those of
the coast are flat; those of the sierra are pitched to facilitate run
off.]
The basic cause of the general aridity of the region has already been
noted; the peculiar circumstances giving origin to the variety in detail
can be briefly stated. They depend upon the meteorologic and
hydrographic features of the adjacent portion of the South Pacific Ocean
and upon the local topography.
The lofty Andes interrupt the broad sweep of the southeast trades
passing over the continent from the Atlantic; and the wind circulation
of the Peruvian Coast is governed to a great degree by the high pressure
area of the South Pacific. The prevailing winds blow from the south and
the southeast, roughly paralleling the coast or, as onshore winds,
making a small angle with it. When the Pacific high pressure area is
best developed (during the southern winter), the southerly direction of
the winds is emphasized, a condition clearly shown on the Pilot Charts
of the South Pacific Ocean, issued by the U.S. Hydrographic Office.
[Illustration: FIG. 76--Temperatures at Callao, June-September, 1912,
from observations taken by Captain A. Taylor, of Callao. Air
temperatures are shown by heavy lines; sea temperatures by light lines.
In view of the scant record for comparative land and water temperatures
along the Peruvian coast this record, short as it is, has special
interest.]
The hydrographic feature of greatest importance is the Humboldt Current.
To its cold waters is largely due the remarkably low temperatures of the
coast.[21] In the latitude of Lima its mean surface temperature is about
10° below normal. Lima itself has a mean annual temperature 4.6° F.
below the theoretical value for that latitude, (12° S.). An accompanying
curve shows the low temperature of Callao during the winter months. From
mid-June to mid-September the mean was 61° F., and the annual mean is
only 65.6° F. (18° C.). The reduction in temperature is accompanied by a
reduction in the vapor capacity of the super-incumbent air, an effect of
which much has been made in explanation of the west-coast desert. That
it is a contributing though not exclusive factor is demonstrated in Fig.
77. Curve _A_ represents the hypothetical change of temperature on a
mountainous coast with temporary afternoon onshore winds from a _warm_
sea. Curve _B_ represents the change of temperature if the sea be cold
(actual case of Peru). The more rapid rise of curve _B_ to the right of
X-X′, the line of transition, and its higher elevation above its former
saturation level, as contrasted with _A_, indicates greater dryness
(lower relative humidity). There has been precipitation in case _A_, but
at a higher temperature, hence more water vapor remains in the air
after precipitation has ceased. Curve _B_ ultimately rises nearly to the
level of _A_, for with less water vapor in the air of case _B_ the
temperature rises more rapidly (a general law). Moreover, the higher the
temperature the greater the radiation. To summarize, curve _A_ rises
more slowly than curve _B_, (1) because of the greater amount of water
vapor it contains, which must have its temperature raised with that of
the air, and thus absorbs energy which would otherwise go to increase
the temperature of the air, and (2) because its loss of heat by
radiation is more rapid on account of its higher temperature. We
conclude from these principles and deductions that under the given
conditions a cold current intensifies, but does not cause the aridity of
the west-coast desert.
[Illustration: FIG. 77--To show progressive lowering of saturation
temperature in a desert under the influence of the mixing process
whereby dry and cool air from aloft sinks to lower levels thus
displacing the warm surface air of the desert. The evaporated moisture
of the surface air is thus distributed through a great volume of upper
air and rain becomes increasingly rarer. Applied to deserts in general
it shows that the effect of any cosmic agent in producing climatic
change from moist to dry or dry to moist will be disproportionately
increased. The shaded areas C and C’ represent the fog-covered slopes of
the Coast Range of Peru as shown in Fig. 92. X-X’ represents the crest
of the Coast Range.]
Curves _a_ and _b_ represent the rise of temperature in two contrasted
cases of warm and cold sea with the coastal mountains eliminated, so as
to simplify the principle applied to _A_ and _B_. The steeper gradient
of _b_ also represents the fact that the lower the initial temperature
the dryer will the air become in passing over the warm land. For these
two curves the transition line X-X’ coincides with the crest of the
Coast Range. It will also be seen that curve _a_ is never so far from
the saturation level as curve _b_. Hence, unusual atmospheric
disturbances would result in heavier and more frequent showers.
[Illustration: FIG. 78--Wind roses for Callao. The figures for the
earlier period (1897-1900) are drawn from data in the Boletín de la
Sociedad Geográfica de Lima, Vols. 7 and 8, 1898-1900: for the latter
period data from observations of Captain A. Taylor, of Callao. The
diameter of the circle represents the proportionate number of
observations when calm was registered.]
[Illustration: FIG. 79--Wind roses for Mollendo. The figures are drawn
from data in Peruvian Meteorology (1892-1895), Annals of the
Astronomical Observatory of Harvard College, Vol. 30, Pt. 2, Cambridge,
Mass., 1906. Observations for an earlier period, Feb. 1889-March 1890,
(Id. Vol. 39, Pt. 1, Cambridge, Mass. 1890) record S. E. wind at 2 p. m.
97 per cent of the observation time.]
[Illustration: FIG. 80--Wind roses for the summer and winter seasons of
the years 1911-1913. The diameter of the circle in each case shows the
proportion of calm. Figures are drawn from data in the Anuario
Meteorológico de Chile, Publications No. 3, (1911), 6 (1912) and 13
(1913), Santiago, 1912, 1914, 1914.]
Turning now to local factors we find on the west coast a regional
topography that favors a diurnal periodicity of air movement. The strong
slopes of the Cordillera and the Coast Range create up-slope or eastward
air gradients by day and opposite gradients by night. To this
circumstance, in combination with the low temperature of the ocean water
and the direction of the prevailing winds, is due the remarkable
development of the sea-breeze, without exception the most important
meteorological feature of the Peruvian Coast. Several graphic
representations are appended to show the dominance of the sea-breeze
(see wind roses for Callao, Mollendo, Arica, and Iquique), but interest
in the phenomenon is far from being confined to the theoretical.
Everywhere along the coast the _virazon_, as the sea-breeze is called in
contradistinction to the _terral_ or land-breeze, enters deeply into the
affairs of human life. According to its strength it aids or hinders
shipping; sailing boats may enter port on it or it may be so violent,
as, for example, it commonly is at Pisco, that cargo cannot be loaded or
unloaded during the afternoon. On the nitrate pampa of northern Chile
(20° to 25° S.) it not infrequently breaks with a roar that heralds its
coming an hour in advance. In the Majes Valley (12° S.) it blows gustily
for a half-hour and about noon (often by eleven o’clock) it settles down
to an uncomfortable gale. For an hour or two before the sea-breeze
begins the air is hot and stifling, and dust clouds hover about the
traveler. The maximum temperature is attained at this time and not
around 2.00 P. M. as is normally the case. Yet so boisterous is the noon
wind that the laborers time their siesta by it, and not by the high
temperatures of earlier hours. In the afternoon it settles down to a
steady, comfortable, and dustless wind, and by nightfall the air is once
more calm.
[Illustration: FIG. 81--Wind roses for Iquique for the summer and winter
seasons of the years 1911-1913. The diameter of the circle in each case
shows the proportion of calm. For source of data see Fig. 80.]
Of highest importance are the effects of the sea-breeze on
precipitation. The bold heights of the Coast Range force the nearly or
quite saturated air of the sea-wind to rise abruptly several thousand
feet, and the adiabatic cooling creates fog, cloud, and even rain on the
seaward slope of the mountains. The actual form and amount of
precipitation both here and in the interior region vary greatly,
according to local conditions and to season and also from year to year.
The coast changes height and contour from place to place. At Arica the
low coastal chain of northern Chile terminates at the Morro de Arica.
Thence northward is a stretch of open coast, with almost no rainfall and
little fog. But in the stretch of coast between Mollendo and the Majes
Valley a coastal range again becomes prominent. Fog enshrouds the hills
almost daily and practically every year there is rain somewhere along
their western aspect.
[Illustration: FIG. 82--The wet and dry seasons of the Coast Range and
the Cordillera are complementary in time. The “wet” season of the former
occurs during the southern winter; the cloud bank on the seaward slopes
of the hills is best developed at that time and actual rains may occur.]
[Illustration: FIG. 83--During the southern summer the seaward slopes of
the Coast Range are comparatively clear of fog. Afternoon cloudiness is
characteristic of the desert and increases eastward (compare Fig. 86),
the influence of the strong sea winds as well as that of the trades
(compare Fig. 93B) being felt on the lower slopes of the Maritime
Cordillera.]
During the southern winter the cloud bank of the coast is best developed
and precipitation is greatest. At Lima, for instance, the clear skies of
March and April begin to be clouded in May, and the cloudiness grows
until, from late June to September, the sun is invisible for weeks at a
time. This is the period of the garua (mist) or the “tiempo de lomas,”
the “season of the hills,” when the moisture clothes them with verdure
and calls thither the herds of the coast valleys.
[Illustration: FIG. 84--Cloudiness at Callao. Figures are drawn from
data in the Boletín de la Sociedad Geográfica de Lima, Vols. 7 and 8,
1898-1900. They represent the conditions at three observation hours
during the summers (Dec., Jan.) of 1897-1898, 1898-1899, 1899-1900 and
the winters (June, July) of 1898 and 1899.]
During the southern summer on account of the greater relative difference
between the temperatures of land and water, the sea-breeze attains its
maximum strength. It then accomplishes its greatest work in the desert.
On the pampa of La Joya, for example, the sand dunes move most rapidly
in the summer. According to the Peruvian Meteorological Records of the
Harvard Astronomical Observatory the average movement of the dunes from
April to September, 1900, was 1.4 inches per day, while during the
summer months of the same year it was 2.7 inches. In close agreement are
the figures for the wind force, the record for which also shows that 95
per cent of the winds with strength over 10 miles per hour blew from a
southerly direction. Yet during this season the coast is generally
clearest of fog and cloud. The explanation appears to lie in the
exceedingly delicate nature of the adjustments between the various
rain-making forces. The relative humidity of the air from the sea is
always high, but on the immediate coast is slightly less so in summer
than in winter. Thus in Mollendo the relative humidity during the winter
of 1895 was 81 per cent; during the summer 78 per cent. Moreover, the
temperature of the Coast Range is considerably higher in summer than in
winter, and there is a tendency to reëvaporation of any moisture that
may be blown against it. The immediate shore, indeed, may still be
cloudy as is the case at Callao, which actually has its cloudiest season
in the summer but the hills are comparatively clear. In consequence the
sea-air passes over into the desert, where the relative increase in
temperature has not been so great (compare Mollendo and La Joya in the
curve for mean monthly temperature), with much higher vapor content than
in winter. The relative humidity for the winter season at La Joya, 1895,
was 42.5 per cent; for the summer season 57 per cent. The influence of
the great barrier of the Maritime Cordillera, aided doubtless by
convectional rising, causes ascent of the comparatively humid air and
the formation of cloud. Farther eastward, as the topographic influence
is more strongly felt, the cloudiness increases until on the border
zone, about 8,000 feet in elevation, it may thicken to actual rain. Data
have been selected to demonstrate this eastern gradation of
meteorological phenomena.
[Illustration: FIG. 85--Temperature curves for Mollendo (solid lines)
and La Joya (broken lines) April, 1894, to December, 1895, drawn from
data in Peruvian Meteorology, 1892-1895, Annals of the Astronomical
Observatory of Harvard College, Vol. 49, Pt. 2, Cambridge, Mass., 1908.
The approximation of the two curves of maximum temperature during the
winter months contrasts with the well-maintained difference in minimum
temperatures throughout the year.]
[Illustration: FIG. 86--Mean monthly cloudiness for Mollendo (solid
line) and La Joya (broken line) from April, 1892, to December, 1895.
Mollendo, 80 feet elevation, has the maximum winter cloudiness
characteristic of the seaward slope of the Coast Range (compare Fig. 82)
while the desert station of La Joya, 4,140 feet elevation, has typical
summer cloudiness (compare Fig. 83). Figures are drawn from data in
Peruvian Meteorology, 1892-1895, Annals of the Astronomical Observatory
of Harvard College, Vol. 49, Pt. 2, Cambridge, Mass., 1908.]
[Illustration: FIG. 87--Wind roses for La Joya for the period April,
1892, to December, 1895. Compare the strong afternoon indraught from the
south with the same phenomenon at Mollendo, Fig. 79. Figures drawn from
data in Peruvian Meteorology, 1892-1895, Annals of the Astronomical
Observatory of Harvard College, Vol. 39, Pt. 2, Cambridge, Mass., 1906.]
At La Joya, a station on the desert northeast of Mollendo at an
elevation of 4,140 feet, cloudiness is always slight, but it increases
markedly during the summer. Caraveli, at an altitude of 5,635 feet,[22]
and near the eastern border of the pampa, exhibits a tendency toward the
climatic characteristics of the adjacent zone. Data for a camp station
out on the pampa a few leagues from the town, were collected by Mr. J.
P. Little of the staff of the Peruvian Expedition of 1912-13. They
relate to the period January to March, 1913. Wind roses for these months
show the characteristic light northwesterly winds of the early morning
hours, in sharp contrast with the strong south and southwesterly
indraught of the afternoon. The daily march of cloudiness is closely
coördinated. Quotations from Mr. Little’s field notes follow:
“In the morning there is seldom any noticeable wind. A breeze starts at
10 A. M., generally about 180° (i. e. due south), increases to 2 or 3
velocity at noon, having veered some 25° to the southwest. It reaches a
maximum velocity of 3 to 4 at about 4.00 P. M., now coming about 225°
(i. e. southwest). By 6 P. M. the wind has died down considerably and
the evenings are entirely free from it. The wind action is about the
same every day. It is not a cold wind and, except with the fog, not a
damp one, for I have not worn a coat in it for three weeks. It has a
free unobstructed sweep across fairly level pampas.... At an interval of
every three or four days a dense fog sweeps up from the southwest, dense
enough for one to be easily lost in it. It seldom makes even a sprinkle
of rain, but carries heavy moisture and will wet a man on horseback in
10 minutes. It starts about 3 P.M. and clears away by 8.00 P. M.....
During January, rain fell in camp twice on successive days, starting at
3.00 P. M. and ceasing at 8.00 P. M. It was merely a light, steady rain,
more the outcome of a dense fog than a rain-cloud of quick approach. In
Caraveli, itself, I am told that it rains off and on all during the
month in short, light showers.” This record is dated early in February
and, in later notes, that month and March are recorded rainless.
[Illustration: FIG. 88--Wind roses for a station on the eastern border
of the Coast Desert near Caraveli during the summer (January to March)
of 1913. Compare with Fig. 87. The diameter of the circle in each case
represents the proportion of calm. Note the characteristic morning
calm.]
Chosica (elevation 6,600 feet), one of the meteorological stations of
the Harvard Astronomical Observatory, is still nearer the border. It
also lies farther north, approximately in the latitude of Lima, and this
in part may help to explain the greater cloudiness and rainfall. The
rainfall for the year 1889-1890 was 6.14 inches, of which 3.94 fell in
February. During the winter months when the principal wind observations
were taken, over 90 per cent showed noon winds from a southerly
direction while in the early morning northerly winds were frequent. It
is also noteworthy that the “directions of the upper currents of the
atmosphere as recorded by the motion of the clouds was generally between
N. and E.” Plainly we are in the border region where climatic influences
are carried over from the plateau and combine their effects with those
from Pacific sources. Arequipa, farther south, and at an altitude of
7,550 feet, resembles Chosica. For the years 1892 to 1895 its mean
rainfall was 5.4 inches.
[Illustration: FIG. 89--Cloudiness at the desert station of Fig. 88
(near Caraveli), for the summer (January to March) of 1913.]
Besides the seasonal variations of precipitation there are longer
periodic variations that are of critical importance on the Coast Range.
At times of rather regular recurrence, rains that are heavy and general
fall there. Every six or eight years is said to be a period of rain, but
the rains are also said to occur sometimes at intervals of four years or
ten years. The regularity is only approximate. The years of heaviest
rain are commonly associated with an unusual frequency of winds from the
north, and an abnormal development of the warm current, El Niño, from
the Gulf of Guayaquil. Such was the case in the phenomenally rainy year
of 1891. The connection is obscure, but undoubtedly exists.
The effects of the heavy rains are amazing and appear the more so
because of the extreme aridity of the country east of them. During the
winter the desert traveler finds the air temperature rising to
uncomfortable levels. Vegetation of any sort may be completely lacking.
As he approaches the leeward slope of the Coast Range, a cloud mantle
full of refreshing promise may be seen just peeping over the crest (Fig.
91). Long, slender cloud filaments project eastward over the margin of
the desert. They are traveling rapidly but they never advance far over
the hot wastes, for their eastern margins are constantly undergoing
evaporation. At times the top of the cloud bank rises well above the
crest of the Coast Range, and it seems to the man from the temperate
zone as if a great thunderstorm were rising in the west. But for all
their menace of wind and rain the clouds never get beyond the desert
outposts. In the summer season the aspect changes, the heavy yellow sky
of the desert displaces the murk of the coastal mountains and the
bordering sea.
[Illustration: FIG. 90--Cloudiness at Chosica, July, 1889, to September,
1890. Chosica, a station on the Oroya railroad east of Lima, is situated
on the border region between the desert zone of the coast and the
mountain zone of yearly rains. The minimum cloudiness recorded about 11
a. m. is shown by a broken line; the maximum cloudiness, about 7 p. m.,
by a dotted line, and the mean for the 24 hours by a heavy solid line.
The curves are drawn from data in Peruvian Meteorology, 1889-1890,
Annals of the Astronomical Observatory of Harvard College, Vol. 39, Pt.
1, Cambridge, Mass., 1899.]
It is an age-old strife renewed every year and limited to a narrow field
of action, wonderfully easy to observe. We saw it in its most striking
form at the end of the winter season in October, 1911, and for more than
a day watched the dark clouds rise ominously only to melt into nothing
where the desert holds sway. At night we camped beside a scum-coated
pool of alkali water no larger than a wash basin. It lay in a valley
that headed in the Coast Range, and carried down into the desert a mere
trickle that seeped through the gravels of the valley floor. A little
below the pool the valley cuts through a mass of granite and becomes a
steep-walled gorge. The bottom is clogged with waste, here boulders,
there masses of both coarse and fine alluvium. The water in the valley
was quite incapable of accomplishing any work except that associated
with solution and seepage, and we saw it in the wet season of an
unusually wet year. Clearly there has been a diminution in the water
supply. But time prevented us from exploring this particular valley to
its head, to see if the reduction were due to a change of climate, or
only to capture of the head-waters by the vigorous rain-fed streams that
enjoy a favorable position on the wet seaward slopes and that are
extending their watershed aggressively toward the east at the expense of
their feeble competitors in the dry belt.
An early morning start enabled me to witness the whole series of changes
between the clear night and the murky day, and to pass in twelve hours
from the dry desert belt through the wet belt, and emerge again into the
sunlit terraces at the western foot of the Coast Range. Two hours before
daylight a fog descended from the hills and the going seemed to be
curiously heavy for the beasts. At daybreak my astonishment was great to
find that it was due to the distinctly moist sand. We were still in the
desert. There was not a sign of a bush or a blade of grass. Still, the
surface layer, from a half inch to an inch thick, was really wet. The
fog that overhung the trail lifted just before sunrise, and at the first
touch of the sun melted away as swiftly as it had come. With it went the
surface moisture and an hour after sunrise the dust was once more rising
in clouds around us.
We had no more than broken camp that morning when a merchant with a
pack-train passed us, and shouted above the bells of the leading animals
that we ought to hurry or we should get caught in the rain at the pass.
My guide, who, like many of his kind, had never before been over the
route he pretended to know, asked him in heaven’s name what drink in
distant Camaná whence he had come produced such astonishing effects as
to make a man talk about rain in a parched desert. We all fell to
laughing and at our banter the stranger stopped his pack-train and
earnestly urged us to hurry, for, he said, the rains beyond the pass
were exceptionally heavy this year. We rode on in a doubtful state of
mind. I had heard about the rains, but I could not believe that they
fell in real showers!
About noon the cloud bank darkened and overhung the border of the
desert. Still the sky above us was clear. Then happened what I can yet
scarcely believe. We rode into the head of a tiny valley that had cut
right across the coast chain. A wisp of cloud, an outlier of the main
bank, lay directly ahead of us. There were grass and bushes not a
half-mile below the bare dry spot on which we stood. We were riding down
toward them when of a sudden the wind freshened and the cloud wisp
enveloped us, shutting out the view, and ten minutes later the moisture
had gathered in little beads on the manes of our beasts and the trail
became slippery. In a half-hour it was raining and in an hour we were in
the midst of a heavy downpour. We stopped and pastured our famished
beasts in luxuriant clover. While they gorged themselves a herd of
cattle drifted along, and a startled band of burros that suddenly
confronted our beasts scampered out of sight in the heavy mist. Later we
passed a herdsman’s hut and long before we reached him he shouted to us
to alter our course, for just ahead the old trail was wet and
treacherous at this time of year. The warning came too late. Several of
our beasts lost their footing and half rolled, half slid, down hill. One
turned completely over, pack and all, and lay in the soft mud calmly
taking advantage of the delay to pluck a few additional mouthfuls of
grass. We were glad to reach firmer ground on the other side of the
valley.
The herdsmen were a hospitable lot. They had come from Camaná and rarely
saw travelers. Their single-roomed hut was mired so deeply that one
found it hard to decide whether to take shelter from the rain inside or
escape the mud by standing in the rain outside. They made a little
so-called cheese, rounded up and counted the cattle on clear days,
drove them to the springs from time to time, and talked incessantly of
the wretched rains in the hills and the delights of dry Camaná down on
the coast. We could not believe that only some hours’ traveling
separated two localities so wholly unlike.
The heavy showers and luxuriant pastures of the wet years and the light
local rains of the dry years endow the Coast Range with many peculiar
geographic qualities. The heavy rains provide the desert people at the
foot of the mountains such a wealth of pasture for their burdensome
stock as many oases dwellers possess only in their dreams. From near and
far cattle are driven to the wet hill meadows. Some are even brought in
from distant valleys by sea, yet only a very small part of the rich
pastures can be used. It is safe to say that they could comfortably
support ten times the number of cattle, mules, and burros that actually
graze upon them. The grass would be cut for export if the weather were
not so continually wet and if there were not so great a mixture of
weeds, flowers, and shrubs.
Then come the dry years. The surplus stock is sold, and what remains is
always maintained at great expense. In 1907 I saw stock grazing in a
small patch of dried vegetation back of Mollendo, although they had to
be driven several miles to water. They looked as if they were surviving
with the greatest difficulty and their restless search for pasture was
like the search of a desperate hunter of game. In 1911 the same tract
was quite devoid of grass, and except for the contour-like trails that
completely covered the hills no one would even guess that this had
formerly been a cattle range. The same year, but five months later, a
carpet of grass, bathed in heavy mist, covered the soil; a trickle of
water had collected in pools on the valley floor; several happy families
from the town had laid out a prosperous-looking garden; there were
romping children who showed me where to pick up the trail to the port;
on every hand was life and activity because the rains had returned
bringing plenty in their train. I asked a native how often he was
prosperous.
“Segun el temporal y la Providencia” (according to the weather and to
Providence), he replied, as he pointed significantly to the pretty green
hills crowned with gray mist.
It, therefore, seems fortunate that the Coast Range is so placed as to
intercept and concentrate a part of the moisture that the sea-winds
carry, and doubly fortunate that its location is but a few miles from
the coast, thereby giving temporary relief to the relatively crowded
people of the lower irrigated valleys and the towns. The wet years
formerly developed a crop of prospectors. Pack animals are cheaper when
there is good pasture and they are also easier to maintain. So when the
rains came the hopeful pick-and-shovel amateurs began to emigrate from
the towns to search for ore among the discolored bands of rock intruded
into the granite masses of the coastal hills. However, the most likely
spots have been so thoroughly and so unsuccessfully prospected for many
years that there is no longer any interest in the “mines.”
Transportation rates are still most intimately related to the rains. My
guide had two prices--a high price if I proposed to enter a town at
night and thus require him to buy expensive forage; a low price if I
camped in the hills and reached the town in time for him to return to
the hills with his animals. Inquiry showed that this was the regular
custom. I also learned that in packing goods from one part of the coast
to another forage must be carried in dry years or the beasts required to
do without. In wet years by a very slight detour the packer has his
beasts in good pasture that is free for all. The merchant who dispatches
the goods may find his charges nearly doubled in extremely dry years.
Goods are more expensive and there is a decreased consumption. The
effects of the rains are thus transmitted from one to another, until at
last nearly all the members of a community are bearing a share of the
burdens imposed by drought. As always there are a few who prosper in
spite of the ill wind. If the pastures fail, live stock _must_ be sold
and the dealers ship south to the nitrate ports or north to the large
coast towns of Peru, where there is always a demand. Their business is
most active when it is dry or rather at the beginning, of the dry
period. Also if transport by land routes becomes too expensive the small
traders turn to the sea routes and the carriers have an increased
business. But so far as I have been able to learn, dry years favor only
a few scattered individuals.
To the traveler on the west coast it is a source of constant surprise
that the sky is so often overcast and the ports hidden by fog, while on
every hand there are clear evidences of extreme aridity. Likewise it is
often inquired why the sunsets there should be often so superlatively
beautiful during the winter months when the coast is fog bound. Why a
desert when the air is so humid? Why striking sunsets when so many of
the days are marked by dull skies? As we have seen in the first part of
this chapter, the big desert tracts lie east of the Coast Range, and
there, excepting slight summer cloudiness, cloudless skies are the rule.
The desert just back of the coast is in many parts of Peru only a narrow
fringe of dry marine terraces quite unlike the real desert in type of
weather and in resources. The fog bank overhanging it forms over the
Humboldt Current which lies off shore; it drifts landward with the
onshore wind; it forms over the upwelling cold water between the current
and the shore; it gathers on the seaward slopes of the coastal hills as
the inflowing air ascends them in its journey eastward. Sometimes it
lies on the surface of the land and the water; more frequently it is
some distance above them. On many parts of the coast its characteristic
position is from 2,000 to 4,000 feet above sea level, descending at
night nearly or quite to the surface, ascending by day and sometimes all
but disappearing except as rain-clouds on the hills.[23] Upon the local
behavior of the fog bank depends in large measure the local climate. A
general description of the coastal climate will have many exceptions.
The physical principles involved are, however, the same everywhere. I
take for discussion therefore the case illustrated by Fig. 92, since
this also displays with reasonable fidelity the conditions along that
part of the Peruvian coast between Camaná and Mollendo which lies in the
field of work of the Yale Peruvian Expedition of 1911.
Three typical positions of the fog bank are shown in the figure, and a
fourth--that in which the bank extends indefinitely westward--may be
supplied by the imagination.
If the cloud bank be limited to _C_ only the early morning hours at the
port are cloudy. If it extend to _B_ the sun is obscured until midday.
If it reach as far west as _A_ only a few late afternoon hours are
sunny. Once in a while there is a sudden splash of rain--a few drops
which astonish the traveler who looks out upon a parched landscape. The
smaller drops are evaporated before reaching the earth. In spite of the
ever-present threat of rain the coast is extremely arid. Though the
vegetation appears to be dried and burned up, the air is humid and for
months the sky may be overcast most of the time. So nicely are the
rain-making conditions balanced that if one of our ordinary low-pressure
areas, or so-called cyclonic storms, from the temperate zone were set in
motion along the foot of the mountains, the resulting deluge would
immediately lay the coast in ruins. The cane-thatched, mud-walled huts
and houses would crumble in the heavy rain like a child’s sand pile
before a rising sea; the alluvial valley land would be coated with
infertile gravel; and mighty rivers of sand, now delicately poised on
arid slopes, would inundate large tracts of fertile soil.
[Illustration: FIG. 91--Looking down the canyon of the Majes River to
the edge of the cloud bank formed against the Coast Range back of
Camaná.]
[Illustration: FIG. 92--Topographic and climatic cross-section to show
the varying positions of the cloud bank on the coast of Peru, the dry
terrace region, and the types of stream profiles in the various belts.]
If the fog and cloud bank extend westward indefinitely, the entire day
may be overcast or the sun appear for a few moments only through
occasional rifts. Generally, also, it will make an appearance just
before sunset, its red disk completely filling the narrow space between
the under surface of the clouds and the water. I have repeatedly seen
the ship’s passengers and even the crew leave the dinner table and
collect in wondering groups about the port-holes and doorways the better
to see the marvelous play of colors between sky and sea. It is
impossible not to be profoundly moved by so majestic a scene. A long
resplendent path of light upon the water is reflected in the clouds.
Each cloud margin is tinged with red and, as the sun sinks, the long
parallel bands of light are shortened westward, changing in color as
they go, until at last the full glory of the sunset is concentrated in a
blazing arc of reds, yellows, and purples, that to most people quite
atones for the dull gray day and its humid air.
At times the clouds are broken up by the winds and scattered
helter-skelter through the west. A few of them may stray into the path
of the sun temporarily to hide it and to reflect its primary colors when
the sun reappears. From the main cloud masses there reach out slender
wind-blown streamers, each one delicately lighted as the sun’s rays
filter through its minute water particles. Many streamers are visible
for only a short distance, but when the sun catches them their filmy
invisible fingers become delicate bands of light, some of which rapidly
grow out almost to the dome of the sky. Slowly they retreat and again
disappear as the rays of the sun are gradually shut off by the upturning
curve of the earth.
The unequal distribution of precipitation in the climatic zones of
western Peru has important hydrographic consequences. These will now be
considered. In the preceding figure four types of stream profiles are
displayed and each has its particular relation to the cloud bank. Stream
1 is formed wholly upon the coastal terraces beneath the cloud bank. It
came into existence only after the uplift of the earth’s crust that
brought the wave-cut platforms above sea level. It is extremely youthful
and on account first of the small seepage at its headquarters--it is
elsewhere wholly without a tributary water supply--and, second, of the
resistant granite that occurs along this part of the coast, it has very
steep and irregular walls and an ungraded floor. Many of these
“quebradas” are difficult to cross. A few of them have fences built
across their floors to prevent the escape of cattle and burros that
wander down from the grassy hills into the desert zone. Others are
partitioned off into corrals by stone fences, the steep walls of the
gorge preventing the escape of the cattle. To these are driven the
market cattle, or mules and burros that are required for relays along
the shore trail.
Stream 2 heads in the belt of rains. Furthermore it is a much older
stream than 1, since it dates back to the time when the Coast Range was
first formed. It has ample tributary slopes and a large number of small
valleys. A trickle of water flows down to become lost in the alluvium of
the lower part of the valley or to reappear in scattered springs. Where
springs and seepage occur together, an olive grove or a garden marks the
spot, a corral or two and a mud or stone or reed hut is near by, and
there is a tiny oasis. Some of these dots of verdure become so dry
during a prolonged drought that the people, long-established, move away.
To others the people return periodically. Still others support permanent
settlements.
Stream 3 has still greater age. Its only competitors are the feeble,
almost negligible, streams that at long intervals flow east toward the
dry zone. Hence it has cut back until it now heads in the desert. Its
widely branched tributaries gather moisture from large tracts. There is
running water in the valley floor even down in the terrace zone. At
least there are many dependable springs and the permanent homes that
they always encourage. A valley of this type is always marked by a
well-defined trail that leads from settlement to settlement and eastward
over the “pass” to the desert and the Andean towns.
Stream 4 is a so-called “antecedent” stream. It existed before the Coast
Range was uplifted and cut its channel downward as the mountains rose in
its path. The stretch where it crosses the mountains may be a canyon
with a narrow, rocky, and uncultivable floor, so that the valley trails
rise to a pass like that at the head of stream 3, and descend again to
the settlements at the mouth of 4. There is in this last type an
abundance of water, for the sources of the stream are in the zone of
permanent snows and frequent winter rains of the lofty Cordillera of the
Andes. The settlements along this stream are continuous, except where
shut-ins occur--narrow, rocky defiles caused by more resistant rock
masses in the path of the stream. Here and there are villages. The
streams have fish. When the water rises the river may be unfordable and
people on opposite sides must resort to boats or rafts.[24]
EASTERN BORDER CLIMATES
On windward mountain slopes there is always a belt of maximum
precipitation whose elevation and width vary with the strength of the
wind, with the temperature, and with the topography. A strong and
constant wind will produce a much more marked concentration of the
rainfall. The belt is at a low elevation in high latitudes and at a high
elevation in low latitudes, with many irregularities of position
dependent upon the local and especially the minimum winter temperature.
The topographic controls are important, since the rain-compelling
elevation may scatter widely the localities of maximum precipitation or
concentrate them within extremely narrow limits. The human effects of
these climatic conditions are manifold. Wherever the heaviest rains are,
there, too, as a rule, are the densest forests and often the most
valuable kinds of trees. If the general climate be favorable and the
region lie near dense and advanced populations, exploitation of the
forest and progress of the people will go hand in hand. If the region be
remote and some or all of the people in a primitive state, the forest
may hinder communication and retard development, especially if it lie in
a hot zone where the natural growth of population is slow.... These are
some of the considerations we shall keep in mind while investigating the
climate of the eastern border of the Peruvian Andes.
[Illustration: FIG. 93A--Cloud types and rainfall belts on the eastern
border of the Peruvian Andes in the dry season, southern winter. The
zone of maximum rainfall extends approximately from 4,000 to 10,000 feet
elevation.]
[Illustration: FIG. 93B--Cloud types and rainfall belts on the eastern
border of the Peruvian Andes in the wet season, southern summer.]
The belt of maximum precipitation on the eastern border of the Andean
Cordillera in Peru lies between 4,000 and 10,000 feet. Judging by the
temporary records of the expedition and especially by the types of
forest growth, the heaviest rains occur around 8,000 feet. It is between
these elevations that the densest part of the Peruvian _montaña_
(forest) is found. The cold timber line is at 10,500 feet with
exceptional extensions of a few species to 12,500 feet. In basins or
deep secluded valleys near the mountain border, a dry timber line occurs
at 3,000 feet with many variations in elevation due to the variable
declivity and exposure of the slopes and degree of seclusion of the
valleys. Elsewhere, the mountain forest passes without a break into the
plains forest with change in type but with little change in density. The
procumbent and suppressed trees of the cold timber line in regions of
heavy winter snows are here absent, for the snows rarely reach below
14,000 feet and even at that elevation they are only light and
temporary. The line of perpetual snow is at 15,000 feet. This permanent
gap of several thousand feet vertical elevation between the zone of snow
and the zone of forest permits the full extension of many pioneer forest
species, which is to say, there is an irregular development of the cold
timber line. It also permits the full use of the pasture belt above the
timber (Fig. 97), hence permanent habitations exist but little below the
snowline and a group of distinctive high-mountain folk enjoys a wide
distribution. There is a seasonal migration here, but it is not
wholesale; there are pastures snow-covered in the southern winter, but,
instead of the complete winter burial of the Alpine meadows of our
western mountains, we have here only a buried upper fringe. All the rest
of the pasture belt is open for stock the year round.
This climatic distinction between the lofty grazing lands of the tropics
and those of the temperate zones is far-reaching. Our mountain forests
are not utilized from above but from below. Furthermore, the chief ways
of communication lead around our forests, or, if through them, only for
the purpose of putting one population group in closer touch with
another. In the Peruvian Andes the largest population groups live above
the forest, not below it or within it. It must be and is exploited from
above.
Hence railways to the eastern valleys of Peru have two chief objects,
(1) to get the plantation product to the dense populations above the
forest and (2) to bring timber from the _montaña_ to the treeless
plateau. The mountain prospector is always near a habitation; the rubber
prospector goes down into the forested valleys and plains far from
habitations. The forest separates the navigable streams from the chief
towns of the plateau; it does not lead down to rich and densely
populated valley floors.
Students in eastern Peru should find it a little difficult to understand
poetical allusions to silent and lonely highlands in contrast to the
busy life of the valleys. To them Shelley’s description of the view from
the Euganean Hills of northern Italy,
“Beneath is spread like a green sea
The waveless plain of Lombardy, ...
Islanded by cities fair,”
might well seem to refer to a world that is upside down.
There is much variation in the forest types between the mountains and
the plains. At the top of the forest zone the warm sunny slopes have a
forest cover; the shady slopes are treeless. At the lower edge of the
grassland, only the shady slopes are forested (Fig. 53B). Cacti of
arboreal size and form grow on the lofty mountains far above the limits
of the true forest; they also appear at 3,000 feet in modified form,
large, rank, soft-spined, and in dense stands on the semi-arid valley
floors below the dry timber line. Large tracts between 8,000 and 10,000
feet are covered with a forest growth distributed by species--here a
dense stand of one type of tree, there another. This is the most
accessible part of the Peruvian forest and along the larger valleys it
is utilized to some extent. The number of species is more limited,
however, and the best timber trees are lower down. Though often referred
to as jungle, the lowlier growths at the upper edge of the forest zone
have no resemblance to the true jungle that crowds the lowland forest.
They are merely an undergrowth, generally open, though in some places
dense. They are nowhere more dense than many examples from New England
or the West.
Where deep valleys occur near the border of the mountains there is a
semi-arid climate below and a wet climate above, with a correspondingly
greater number of species within short distances of each other. This is
a far more varied forest than at the upper edge of the timber zone or
down on the monotonous plains. It has a higher intrinsic value than any
other. That part of it between the Pongo and Yavero (1,200 to 4,000
feet) is very beautiful, with little undergrowth except a light
ground-cover of ferns. The trees are from 40 to 100 feet in height with
an average diameter of about 15 inches. It would yield from 3,000 to
5,000 board feet per acre exclusive of the palms. There are very few
vines suspended from the forest crown and the trunks run clear from 30
to 60 feet above the ground. Were there plenty of labor and a good
transportation line, these stands would have high economic value. Among
the most noteworthy trees are the soft white cedar, strong and light;
the amarillo and the sumbayllo, very durable in water; the black nogal,
and the black balsam, straight and easy to work; the heavy yunquero,
which turns pink when dry; the chunta or black palm, so hard and
straight and easy to split that wooden nails are made from it; and the
rarer sandy matico, highly prized for dug-out canoes. Also from the
chunta palm, hollow except for a few central fibers, easily removed,
pipes are made to convey water. The cocobolo has a rich brown color and
a glossy surface and is very rare, hence is much sought after for use in
furniture making. Most of these woods take a brilliant polish and
exhibit a richness and depth of color and a beauty of grain that are
rare among our northern woods.
[Illustration: FIG. 94--Cloud belt at 11,000 feet in the Apurimac Canyon
near Incahuasi. For a regional diagram and a climatic cross-section see
Figs. 32 and 33.]
[Illustration: FIG. 95--The tropical forest near Pabellon on the slopes
of the Urubamba Valley. Elevation 3,000 feet (915 m.).]
The plains forest northeast of the mountains is in the zone of moderate
rainfall where there is one long dry season and one long wet season.
When it is dry the daytime temperatures rise rapidly to such high levels
that the relative humidity of the air falls below 50 per cent (Fig.
110). The effect on the vegetation is so marked that many plants pass
into a distinctly wilted condition. On clear days the rapid fall in the
relative humidity is astonishing. By contrast the air on the mountain
border heats more slowly and has a higher relative humidity, because
clouds form almost constantly in the ascending air currents and reflect
and absorb a large part of the heat of the sun’s rays. It is striking to
find large tracts of cane and bamboo on the sand bars and on wet shady
hillslopes in the slope belt, and to pass out of them in going to the
plains with which we generally associate a swamp vegetation. They exist
on the plains, but only in favored, that is to say wet, spots. Larger
and more typical tracts grow farther north where the heavier rains of
the Amazon basin fall.
The floods of the wet tropical season also have a restricting influence
upon the tropical forest. They deliver such vast quantities of water to
the low-gradient lowland streams that the plains rivers double, even
treble, their width and huge pools and even temporary lakes form in the
shallow depressions back of the natural levees. Of trees in the flooded
areas there are only those few species that can grow standing in water
several months each year. There are also cane and bamboo, ferns in
unlimited numbers, and a dense growth of jungle. These are the haunts of
the peccary, the red forest deer, and the jungle cat. Except along the
narrow and tortuous animal trails the country is quite impassable. Thus
for the sturdiest and most useful forest growth the one-wet-one-dry
season zone of the plains has alternately too much and too little water.
The rubber tree is most tolerant toward these conditions. Some of the
best stands of rubber trees in Amazonia are in the southwestern part of
the basin of eastern Peru and Bolivia, where there is the most typical
development of the habitat marked by the seasonal alternation of floods
and high temperatures.
When tropical agriculture is extended to the plains the long dry season
will be found greatly to favor it. The southwestern quadrant of the
Amazon basin, above referred to, is the best agricultural area within
it. The northern limits of the tract are only a little beyond the Pongo.
Thence northward the climate becomes wetter. Indeed the best tracts of
all extend from Bolivia only a little way into southeastern Peru, and
are coincident with the patchy grasslands that are there interspersed
with belts of woodland and forest. Sugar-cane is favored by a climate
that permits rapid growth with a heavy rainfall and a dry season is
required for quality and for the harvest. Rice and a multitude of
vegetable crops are also well suited to this type of climate. Even corn
can be grown in large quantities.
At the present time tropical agriculture is almost wholly confined to
the mountain valleys. The reasons are not wholly climatic, as the above
enumeration of the advantages of the plains suggests. The consuming
centers are on the plateau toward the west and limitation to mule pack
transport always makes distance in a rough country a very serious
problem. The valleys combine with the advantage of a short haul a
climate astonishingly like the one just described. In fact it is even
more extreme in its seasonal contrasts. The explanation is dependent
upon precisely the same principles we have hitherto employed. The front
range of the Andes and the course of the Urubamba run parallel for some
distance. Further, the front range is in many places somewhat higher
than the mountain spurs and knobs directly behind it. Even when these
relations are reversed the front range still acts as a barrier to the
rains for all the deep valleys behind it whose courses are not directly
toward the plains. Thus, one of the largest valleys in Peru, the
Urubamba, drops to 3,400 feet at Santa Ana and to 2,000 feet at
Rosalina, well within the eastern scarp of the Andes. The mountains
immediately about it are from 6,000 to 10,000 feet high. The result is a
deep semi-arid pocket with only a patchy forest (Fig. 54, p. 79).[25] In
places the degree of seclusion from the wind is so great that the scrub,
cacti, and irrigation remind one strongly of the desert on the border of
an oasis, only here the transition is toward forests instead of barren
wastes. The dense forest, or _montaña_, grows in the zone of clouds and
maximum precipitation between 4,000 and 10,000 feet. At the lower limit
it descends a thousand feet farther on shady slopes than it does on
sunny slopes. The continuous forest is so closely restricted to the
cloud belt that in Fig. 99 the two limits may be seen in one photograph.
All these sharply defined limits and contrasts are due to the fact that
the broad valley, discharging through a narrow and remote gorge, is
really to leeward of all the mountains around it. It is like a real
desert basin except in a lesser degree of exclusion from the rains. If
it were narrow and small the rains formed on the surrounding heights
would be carried over into it. Rain on the hills and sunshine in the
valley is actually the day-by-day weather of the dry season. In the wet
season the sky is overcast, the rains are general, though lighter in the
valley pocket, and plants there have then their season of most rapid
growth. The dry season brings plants to maturity and is the time of
harvest. Hence sugar and cacao plantations on a large scale, hence a
varied life in a restricted area, hence a distinct geographic province
unique in South America.
INTER-ANDEAN VALLEY CLIMATES
Not all the deep Andean valleys lie on or near the eastern border. Some,
like the Apurimac and the Marañon, extend well into the interior of the
Cordillera. Besides these deep remote valleys with their distinct
climatic belts are basins, most of them with outlets to the sea--broad
structural depressions occurring in some cases along large and in others
along small drainage lines. The Cuzco basin at 11,000 feet and the
Abancay basin at 6,000 to 8,000 feet are typical. Both have abrupt
borders, narrow outlets, large bordering alluvial fans, and fertile
irrigable soil. Their difference of elevation occurs at a critical
level. Corn will ripen in the Cuzco basin, but cane will not. Barley,
wheat, and potatoes are the staple crops in the one; sugar-cane,
alfalfa, and fruit in the other. Since both are bordered by high
pastures and by mineralized rocks, the deeper Abancay basin is more
varied. If it were not so difficult to get its products to market by
reason of its inaccessibility, the Abancay basin would be the more
important. In both areas there is less rainfall on the basin floor than
on the surrounding hills and mountains, and irrigation is practised, but
the deeper drier basin is the more dependent upon it. Many small high
basins are only within the limits of potato cultivation. They also
receive proportionately more rain. Hence irrigation is unnecessary.
According as the various basins take in one or another of the different
product levels (Fig. 35) their life is meager and unimportant or rich
and interesting.
The deep-valley type of climate has the basin factors more strongly
developed. Below the Canyon of Choqquequirau, a topographic feature
comparable with the Canyon of Torontoy, the Apurimac descends to 3,000
feet, broadens to several miles, and has large alluvial fans built into
it. Its floor is really arid, with naked gravel and rock, cacti stands,
and gnarled shrubs as the chief elements of the landscape. Moreover the
lower part of the valley is the steeper. A former erosion level is
indicated in Fig. 125. When it was in existence the slopes were more
moderate than now and the valley broad and open. Thereupon came uplift
and the incision of the stream to its present level. As a result, a
steep canyon was cut in the floor of a mature valley. Hence the slopes
are in a relation unlike that of most of the slopes in our most familiar
landscapes. The gentle slopes are above, the steep below. The break
between the two, a topographic unconformity, may be distinctly traced.
[Illustration: FIG. 96--Snow-capped mountain, Soiroccocha, north of
Arma, Cordillera Vilcapampa. The blue glacier ice descends almost to the
edge of a belt of extraordinary woodland growing just under the
snowline. The glacier is seen to overhang the valley and to have built
on the steep valley wall terminal moraines whose outer slopes are almost
precipitous.]
[Illustration: FIG. 97--Shrubby vegetation mixed with grass at 14,000
feet (4,270 m.) on the northern or sunny slopes of the Cordillera
Vilcapampa above Pampaconas, a thousand feet below the snowline. The
grass is remarkably profuse and supports the flocks and herds of a
pastoral population.]
[Illustration: FIG. 98--Dense ground cover, typical trees, epiphytes,
and parasites of the tropical rain forest at 2,500-3,000 feet between
Pongo de Mainique and Rosalina.]
[Illustration: FIG. 99--The Urubamba Valley below Santa Ana. On the dry
valley floor is a mixed growth of scattered trees, shrubs and grass,
with shrubs predominating. Higher up a more luxuriant ravine vegetation
appears. On the upper spurs true forest patches occupy the shady slopes.
Finally, in the zone of clouds at the top of the picture is a continuous
forest. See Fig. 17, for regional applications.]
Combined with these topographic features are certain climatic features
of equal precision. Between 7,000 and 13,000 feet is a zone of clouds
oftentimes marked out as distinctly as the belt of fog on the Peruvian
coast.[26] Rarely does it extend across the valley. Generally it hangs
as a white belt on the opposite walls. When the up-valley winds of day
begin to blow it drifts up-valley, oftentimes to be dissolved as it
strikes the warmer slopes of the upper valley, just as its settling
under surface is constantly being dissolved in the warm dry air of the
valley floor. Where the precipitation is heaviest there is a belt of
woodland--dark, twisted trees, moss-draped, wet--a Druid forest. Below
and above the woodland are grassy slopes. At Incahuasi a spur runs out
and down until at last it terminates between two deep canyons. No
ordinary wells could be successful. The ground water must be a thousand
feet down, so a canal, a tiny thing only a few inches wide and deep, has
been cut away up to a woodland stream. Thence the water is carried down
by a contour-like course out of the woodland into the pasture, and so
down to the narrow part of the spur where there is pasture but no
springs or streams.
Corn fields surround the few scattered habitations that have been built
just above the break or shoulder on the valley wall where the woodland
terminates, and there are fine grazing lands. The trails follow the
upper slopes whose gentler contours permit a certain liberty of
movement. Then the way plunges downward over a staircase trail, over
steep boulder-strewn slopes to the arid floor of a tributary where
nature has built a graded route. And so to the still more arid floor of
the main valley, where the ample and moderate slopes of the alluvial
fans with their mountain streams permit plantation agriculture again to
come in.
To these three climates, the western border type, the eastern border
type, and the inter-Andean type, we have given chief attention because
they have the most important human relations. The statistical records of
the expedition as shown in the curves and the discussion that
accompanies them give attention to those climatic features that are of
theoretical rather than practical interest, and are largely concerned
with the conventional expression of the facts of weather and climate.
They are therefore combined in the following chapter which is devoted
chiefly to a technical discussion of the meteorology as distinguished
from the climatology of the Peruvian Andes.
CHAPTER X
METEOROLOGICAL RECORDS FROM THE PERUVIAN ANDES
INTRODUCTION
The data in this chapter, on the weather and climate of the Peruvian
Andes, were gathered under the usual difficulties that accompany the
collection of records at camps scarcely ever pitched at the same
elevation or with the same exposure two days in succession. Some of
them, and I may add, the best, were contributed by volunteer observers
at fixed stations. The observations are not confined to the field of the
Yale Peruvian Expedition of 1911, but include also observations from
Professor Hiram Bingham’s Expeditions of 1912 and 1914-15, together with
data from the Yale South American Expedition of 1907. In addition I have
used observations supplied by the Morococha Mining Company through J. P.
Little. Some hitherto unpublished observations from Cochabamba, Bolivia,
gathered by Herr Krüger at considerable expense of money for instruments
and of time from a large business, are also included, and he deserves
the more credit for his generous gift of these data since they were
collected for scientific purposes only and not in connection with
enterprises in which they might be of pecuniary value. My only excuse to
Herr Krüger for this long delay in publication (they were put into my
hands in 1907) is that I have wanted to publish his data in a dignified
form and also to use them for comparison with the data of other climatic
provinces.
A further word to the reader seems necessary before he examines the
following curves and tables. It would be somewhat audacious to assume
that these short-term records have far-reaching importance. Much of
their value lies in their organization with respect to the data already
published on the climate of Peru. But since this would require a delay
of several years in their publication it seems better to present them
now in their simplest form. After all, the professional climatologist,
to whom they are chiefly of interest, scarcely needs to have such
organization supplied to him. Then, too, we hope that there will become
available in the next ten or fifteen years a vastly larger body of
climatological facts from this region. When these have been collected we
may look forward to a volume or a series of volumes on the “Climate of
Peru,” with full statistical tables and a complete discussion of them.
That would seem to be the best time for the reproduction of the detailed
statistics now on hand. It is only necessary that there shall be
sufficient analysis of the data from time to time to give a general idea
of their character and to indicate in what way the scope of the
observations might profitably be extended. I have, therefore, taken from
the available facts only such as seem to me of the most importance
because of their unusual character or their special relations to the
boundaries of plant provinces or of the so-called “natural regions” of
geography.
MACHU PICCHU[27]
The following observations are of special interest in that they
illustrate the weather during the southern winter and spring at the
famous ruins of Machu Picchu in the Canyon of Torontoy. The elevation is
8,500 feet. The period they cover is too short to give more than a hint
of the climate or of the weather for the year. It extends from August
20, 1912, to November 6, 1912 (79 days).
ANALYTICAL TABLE OF WIND DIRECTIONS, MACHU PICCHU, 1912
-----------+--------------------------------------------------------+
| Number of Observations |
Direction +----------------------------+---------------------------|
of wind | Aug. 20 -- Sept. 30 | Oct. 1 -- Nov. 6 |
| 7 a. m. 1 p. m. 7 p. m. | 7 a. m. 1 p. m. 7 p. m. |
-----------+----------------------------+---------------------------+
N. | 5 2 5 | 2 -- -- |
N.W. | 9 10 14 | 4 6 11 |
W. | -- 1 2 | 2 2 4 |
S. W. | -- -- 1 | 1 1 6 |
S. | -- -- 1 | -- -- 2 |
S. E. | 4 2 1 | -- -- 3 |
E. | 6 3 3 | 12 4 4 |
N. E. | 8 7 6 | 4 1 3 |
CALM | -- -- 2 | 5 3 3 |
-----------+----------------------------+---------------------------+
----------------------------------------------------------------+
| Percentages of Total Observation[28] |
Direction|------------------------------------------------------|
of wind | Aug. 20 ---- Sept. 30 | Oct. 1 ---- Nov. 6 |
| 7 a. m. 1 p.m. 7 p. m. | 7 a. m. 1 p. m. 7 p. m.|
----------------------------------------------------------------|
N. | 15.6 8.0 14.2 | 6.7 ---- ---- |
N. W. | 28.1 40.0 40.0 | 13.3 35.3 30.7 |
W. | ---- 4.0 5.7 | 6.7 11.8 11.1 |
S. W. | ---- ---- 2.8 | 3.3 5.9 16.7 |
S. | ---- ---- 2.8 | ---- ---- 5.5 |
S. E. | 12.5 8.0 2.8 | ---- ---- 8.3 |
E. | 18.8 12.0 8.6 | 40.0 23.5 11.1 |
N. E. | 25.0 28.0 17.1 | 13.3 5.9 8.3 |
CALM | ---- ---- 5.7 | 16.7 17.6 8.3 |
----------------------------------------------------------------+
[Illustration: FIG. 100--Wind roses for Machu Picchu, August 20 to
November 6, 1912.]
The high percentage of northwest winds during afternoon hours is due to
the up-valley movement of the air common to almost all mountain borders.
The air over a mountain slope is heated more than the free air at the
same elevation over the plains (or lower valley); hence a barometric
gradient towards the mountain becomes established. At Machu Picchu the
Canyon of Torontoy trends northwest, making there a sharp turn from an
equally sharp northeast bend directly upstream. The easterly components
are unrelated to the topography. They represent the trades. If a wind
rose were made for still earlier morning hours these winds would be more
faithfully represented. That an easterly and northeasterly rather than a
southeasterly direction should be assumed by the trades is not difficult
to believe when we consider the trend of the Cordillera--southeast to
northwest. The observations from here down to the plains all show that
there is a distinct change in wind direction in sympathy with the larger
features of the topography, especially the deep valleys and canyons, the
trades coming in from the northeast.
CLOUDINESS
It will be seen that the sky was overcast or a fog lay in the valley 53
per cent of the time at early morning hours. Even at noon the sky was at
no time clear, and it was more than 50 per cent clear only 18 per cent
of the time. Yet this is the so-called “dry” season of the valleys of
the eastern Andes. The rainfall record is in close sympathy. In the 79
days’ observations rain is recorded on 50 days with a greater proportion
from mid-September to the end of the period (November 6), a distinct
transition toward the wet period that extends from December to May. The
approximate distribution of the rains by hours of observation (7 A. M.,
1 P. M., 7 P. M.) was in the ratio 4:3:6. Also the greatest number of
heavy showers as well as the greatest number of showers took place in
the evening. The rainfall was apparently unrelated to wind direction in
the immediate locality, though undoubtedly associated with the regional
movement of the moist plains air toward the mountains. All these facts
regarding clouds and rain plainly show the location of the place in the
belt of maximum precipitation. There is, therefore, a heavy cover of
vegetation. While the situation is admirable for defence, the murky
skies and frequent fogs somewhat offset its topographic surroundings as
a lookout.
ANALYTICAL TABLE OF THE STATE OF THE SKY, MACHU PICCHU, 1912
---------------+-------------+-------------+
| Morning | Total |
---------------+------+------+------+------+
|Aug.- |Oct.- |Days | % |
|Sept. |Nov. | | |
---------------+------+------+------+------+
Foggy | 3.0 | 14.0 | 17.0 | 28.4 |
Overcast | 12.0 | 3.0 | 15.0 | 25.0 |
50-100% cloudy | 4.0 | 10.0 | 14.0 | 23.3 |
0-50% cloudy | 6.0 | 4.0 | 10.0 | 16.7 |
Clear | 3.0 | 1.0 | 4.0 | 6.6 |
---------------+------+------+------+------+
---------------+-------------+-------------+
| Noon | Total |
---------------+------+------+------+------+
|Aug.- |Oct.- | Days | % |
|Sept. |Nov. | | |
---------------+------+------+------+------+
Foggy | 1.0 | -- | 1.0 | 2.6 |
Overcast | 6.0 | 8.0 | 14.0 | 36.8 |
50-100% cloudy | 0.0 | 7.0 | 16.0 | 42.2 |
0-50% cloudy | 5.0 | 2.0 | 7.0 | 18.4 |
Clear | 0.0 | 0.0 | 0.0 | 0.0 |
---------------+------+------+------+------+
---------------+-------------+-------------
| Evening | Total
---------------+------+------+------+------
|Aug.- |Oct.- |Days | %
|Sept. |Nov. | |
---------------+------+------+------+------
Foggy | 1.0 | 2.0 | 3.0 | 4.3
Overcast | 13.0 | 11.0 | 24.0 | 34.8
50-100% cloudy | 8.0 | 15.0 | 23.0 | 33.3
0-50% cloudy | 9.0 | 4.0 | 13.0 | 18.8
Clear | 3.0 | 3.0 | 6.0 | 8.8
---------------+------+------+------+------
SANTA LUCIA[29]
Santa Lucia is a mining center in the province of Puno (16° S.), at the
head of a valley here running northeast towards Lake Titicaca. Its
elevation, 15,500 feet above sea level, confers on it unusual interest
as a meteorological station. A thermograph has been installed which
enables a closer study of the temperature to be made than in the case of
the other stations. It is unfortunate, however, that the observations
upon clouds, wind directions, etc., should not have been taken at
regular hours. The time ranges from 8.30 to 11.30 for morning hours and
from 2.30 to 5.30 for afternoon. The observations cover portions of the
years 1913 and 1914.
TEMPERATURE
Perhaps the most striking features of the weather of Santa Lucia are the
highly regular changes of temperature from night to day or the uniformly
great diurnal range and the small differences of temperature from day to
day or the low diurnal variability. For the whole period of nearly a
year the diurnal variability never exceeds 9.5° F. (5.3° C.) and for
days at a time it does not exceed 2-3° F. (1.1°-1.7° C.). The most
frequent variation, occurring on 71 per cent of the total number of
days, is from 0-3° F., and the mean for the year gives the low
variability of 1.9° F. (1.06° C.). These facts, illustrative of a type
of weather comparable in _uniformity_ with low stations on the Amazon
plains, are shown in the table following as well as in the accompanying
curves.
FREQUENCY OF THE DIURNAL VARIABILITY, SANTA LUCIA, 1913-14
----------+----+----+----+----+-----+
| | | | | |
Degrees F.|May |June|July|Aug.|Sept.|
----------+----+----+----+----+-----+
0 | -- | 2 | 6 | 3 | 4 |
0-1 | 2 | 7 | 7 | 5 | 6 |
1-2 | 11 | 5 | 7 | 11 | 7 |
2-3 | 2 | 8 | 8 | 9 | 3 |
3-4 | 4 | 4 | 2 | 1 | 4 |
4-5 | 1 | 3 | 1 | -- | 2 |
Over 5 | -- | 1 | -- | 2 | 4 |
----------+----+----+----+----+-----+
Days per| 20 | 30 | 31 | 31 | 30 |
month| | | | | |
----------+----+----+----+----+-----+
----------+----+----+----+----+----+-----++---------
| | | | | | ||Total No.
Degrees F.|Oct.|Nov.|Dec.|Jan.|Feb.|March||of days
----------+----+----+----+----+----+-----++---------
0 | 6 | 2 | -- | 1 | -- | 2 || 26
0-1 | 4 | 8 | 12 | 14 | 9 | 5 || 79
1-2 | 8 | 5 | 5 | 4 | 9 | 13 || 85
2-3 | 7 | 7 | 5 | 5 | 4 | 6 || 64
3-4 | 1 | 3 | 6 | 2 | 4 | 2 || 33
4-5 | 1 | 3 | -- | 2 | 1 | 1 || 15
Over 5 | 4 | 2 | 2 | 3 | 1 | -- || 19
----------+----+----+----+----+----+-----++---------
Days per| 31 | 30 | 30 | 31 | 28 | 29 || 321
month| | | | | | ||
----------+----+----+----+----+----+-----++---------
If we take the means of the diurnal variations by months we have a still
more striking curve showing how little change there is between
successive days. June and December are marked by humps in the curve.
They are the months of extreme weather when for several weeks the
temperatures drop to their lowest or climb to their highest levels.
Moreover, there is at these lofty stations no pronounced lag of the
maximum and minimum temperatures for the year behind the times of
greatest and least heating such as we have at lower levels in the
temperate zone. Thus we have the highest temperature for the year on
December 2, 70.4° F. (21.3° C.), the lowest on June 3, 0.2° F. (--17.7°
C.). The daily maxima and minima have the same characteristic. Radiation
is active in the thin air of high stations and there is a very direct
relation between the times of greatest heat received and greatest heat
contained. The process is seen at its best immediately after the sun is
obscured by clouds. In five minutes I have observed the temperature drop
20° F. (11.1° C.) at 16,000 feet (4,877 m.); and a drop of 10° F. (5.6°
C.) is common anywhere above 14,000 feet (4,267 m.). In the curves of
daily maximum and minimum temperatures we have clearly brought out the
uniformity with which the maxima of high-level stations rise to a mean
level during the winter months (May-August). Only at long intervals is
there a short series of cloudy days when the maximum is 10°-12° F.
(5.6°-6.7° C.) below the normal and the minimum stands at abnormally
high levels. Since clouds form at night in quite variable amounts--in
contrast to the nearly cloudless days--there is a far greater
variability among the minimum temperatures. Indeed the variability of
the winter minima is greater than that of the summer minima, for at the
latter season the nightly cloud cover imposes much more stable
atmospheric temperatures. The summer maxima have a greater degree of
variability. Several clear days in succession allow the temperature to
rise from 5°-10° F. (2.8°-5.6° C.) above the winter maxima. But such
extremes are rather strictly confined to the height of the summer
season--December and January. For the rest of the summer the maxima rise
only a few degrees above those of the winter. This feature of the
climate combines with a December maximum of rainfall to limit the period
of most rapid plant growth to two months. Barley sown in late November
could scarcely mature by the end of January, even if growing on the
Argentine plains and much less at an elevation which carries the night
temperatures below freezing at least once a week and where the mean
temperature hovers about 47° F. (8.3° C.). The proper conditions for
barley growing are not encountered above 13,000 to 13,500 feet and the
farmer cannot be certain that it will ripen above 12,500 feet in the
latitude of Santa Lucia.
The curve of mean monthly temperatures expresses a fact of great
importance in the plant growth at high situations in the Andes--the
sharp break between the winter and summer seasons. There are no real
spring and autumn seasons. This is especially well shown in the curve
for non-periodic mean monthly range of temperature for the month of
October. During the half of the year that the sun is in the southern
hemisphere the sun’s noonday rays strike Santa Lucia at an angle that
varies between 0° and 16° from the vertical. The days and nights are of
almost equal length and though there is rapid radiation at night there
is also rapid insolation by day. When the sun is in the northern
hemisphere the days are shortened from one to two hours and the angle of
insolation decreased, whence the total amount of heat received is so
diminished that the mean monthly temperature lies only a little above
freezing point. In winter the quiet pools beside the springs freeze over
long before dark as the hill shadows grow down into the high-level
valleys, and by morning ice also covers the brooks and marshes. Yet the
sun and wind-cured _ichu_ grass lives here, pale green in summer,
straw-yellow in winter. The tola bush also grows rather abundantly. But
we are almost at the upper limit of the finer grasses and a few hundred
feet higher carries one into the realm of the snowline vegetation,
mosses and lichens and a few sturdy flowering plants.
For convenience in future comparative studies the absolute extremes are
arranged in the following table:
[Illustration: FIG. 101 A--DIURNAL TEMPERATURE, SANTA LUCIA, 1913-’14
C--DIURNAL RANGE OF TEMPERATURE, SANTA LUCIA, 1913-’14 E--DIURNAL
VARIABILITY OF TEMPERATURE, SANTA LUCIA, 1913-’14 B--MEAN MONTHLY
TEMPERATURE, SANTA LUCIA, 1913-’14 D--MONTHLY MEANS OF DIURNAL RANGE OF
TEMPERATURE, SANTA LUCIA, 1913-’14 F--RELATIVE HUMIDITY, SANTA LUCIA,
1913-’14]
ABSOLUTE MONTHLY EXTREMES, SANTA LUCIA, 1913-14
-----------------------+----------++----------+----------------
Date | Highest || Lowest | Date
-----------------------+----------++----------+----------------
May[30] (12) | 62° F. || 9° F. | May (25, 26)
June (4 days) | 60° F. || 0.2° F. | June (3)
July (4 days, 31) | 60° F. || 5° F. | July (8)
Aug. (8, 26) | 62° F. || 4° F. | Aug. (4, 5)
Sept. (several days) | 62° F. || 7° F. | Sept. (4 days)
Oct. (24) | 63° F. || 10° F. | Oct. (12, 13)
Nov. (11)[31] | 63° F. || 24.0° F. | Nov. (29)
Dec. (2) | 70.4° F. || 22.2° F. | Dec. (14)
Jan. (19) | 69.5° F. || 26.5° F. | Jan. (3, 15)
Feb. (16, 18) | 63.2° F. || 30.5° F. | Feb. (23)
March (8) | 68.4° F. || 28.5° F. | March (6)
-----------------------+----------++----------+----------------
RAINFALL
The rainfall record for Santa Lucia is for the year beginning November,
1913. For this period the precipitation amounts to 24.9 inches of which
over 85 per cent fell in the rainy season from November to March. Most
of the rain fell during the violent afternoon tempests that characterize
the summer of these high altitudes.
The rainfall of Santa Lucia for this first year of record approximates
closely to the yearly mean of 23.8 inches for the station of Caylloma in
the adjacent province of that name. Caylloma is the center of a mining
district essentially similar to Santa Lucia though the elevation of its
meteorological station, 14,196 feet (4,330 m.), is lower. It is one of
the few Peruvian stations for which a comparatively long series of
records is available. The _Boletín de la Sociedad Geográfica de
Lima_[32] contains a résumé of rainfall and temperature for seven years,
1896-7 to 1902-3. Later data may be found in subsequent volumes of the
same publication but they have not been summarized or in any way
prepared for analysis and they contain several typographical errors. A
graphic representation of the monthly rainfall for the earlier period is
here reproduced from the _Boletín de minas del Perú_.[33] The amount
of precipitation fluctuates considerably from year to year. For the
earlier period, with a mean of 23.8 inches the minimum (1896-7) was 8
inches and the maximum (1898-9) 36 inches. For the later period, 1903-4
to 1910-11, with a mean of 29.5 inches the minimum (1904-5) was 17.5
inches and the maximum (1906-7) was 43 inches.
[Illustration: FIG. 102--Monthly rainfall of Santa Lucia for the year
November, 1913, to October, 1914. No rain fell in July and August.]
[Illustration: FIG. 103A--Maximum, mean and minimum monthly rainfall of
Caylloma for the period 1896-7 to 1902-3. July was absolutely rainless.
Caylloma is situated immediately east of the crest of the Maritime
Cordillera in a position similar to that of Santa Lucia (see Fig. 66).]
[Illustration: FIG. 103B--Annual rainfall of Caylloma for the periods
1896-7 to 1902-3; 1903-4 to 1910-11 and for 1915-6 (incomplete: May and
June, months of low rainfall, are missing). Means for the respective
seven and eight year periods are shown and the rainfall of Santa Lucia
for the single observation year is inserted for comparison.]
RAINFALL, SANTA LUCIA, NOV. 1913 TO OCT. 1914
---------+---------+----------+----------+---------------
|No of |No. of |Max. for |Total rainfall
|fine days|rainy days|single day|in inches
---------+---------+----------+----------+---------------
November | 9 | 21 | 1.150 | 4.264[34]
December | 16 | 15 | .700 | 6.439
January | 17 | 14 | .610 | 3.313
February | 9 | 17 | .910 | 2.975
March | 11 | 20 | 1.102 | 4.381
April | 17 | 13 | 0.31 | 0.92
May | 8 | 23 | 0.35 | 1.63
June | 27 | 3 | 0.05 | 0.07
July | 31 | 0 | 0.00 | 0.00
August | 31 | 0 | 0.00 | 0.00
September| 23 | 7 | 0.05 | 0.35
October | 21 | 10 | 0.14 | 0.56
---------+---------+----------+----------+---------------
Total | | | | 24.902
---------+---------+----------+----------+---------------
WIND
An analysis of the wind at Santa Lucia shows an excess of north and
south winds over those of all other directions. The wind-rose for the
entire period of observation (Fig. 104) clearly expresses this fact.
When this element is removed we observe a strongly seasonal distribution
of the wind. The winter is the time of north and south winds. In summer
the winds are chiefly from the northeast or the southwest. Among single
months, August and February show this fact clearly as well as the less
decisive character of the summer (February) wind.
The mean wind velocity for the month of February was 540 meters per
minute for the morning and 470 meters per minute for the afternoon. The
higher morning rate, an unusual feature of the weather of high
stations, or indeed of wind-phenomena in general, is due, however, to
exceptional changes in wind strength on two days of the month, the 16th
and 25th, when the velocity decreased from a little less than a thousand
meters per minute in the morning to 4 and 152 meters respectively in the
afternoon. More typical is the March record for 1914 at Santa Lucia,
when the wind was _always_ stronger in the afternoon than in the
morning, their ratios being 550 to 510.
[Illustration: Fig. 104--Monthly wind roses for Santa Lucia, June, 1913,
to July, 1914, and composite rose for the whole period of observation.]
CLOUD
The greater strength of the afternoon wind would lead us to suppose that
the cloudiness, which in the trade-wind belt, is to so great an extent
dependent on the wind, is greatest in the afternoon. The diagrams bring
out this fact. Barely is the sky quite clear after the noon hour. Still
more striking is the contrast between the morning and afternoon if we
combine the two densest shadings of the figures. Light, high-lying
cirrus clouds are most characteristic of early morning hours. They
produce some very striking sky effects just before sunrise as they catch
the sun’s rays aloft. An hour or two after sunrise they disappear and
small cumulus clouds begin to form. These grow rapidly as the winds
begin and by afternoon become bulky and numerous. In the wet season they
grow into the nimbus and stratus types that precede a sudden downpour of
water or a furious hailstorm. This is best seen from the base of a
mountain range looking towards the crest, where the cloud-and
rain-making processes of this type are most active.
CLOUD ANALYSIS, SANTA LUCIA
--------------+---------+---------+---------+---------+---------++---------+
| Nov. | Dec. | Jan. | Feb. | March || Total |
Type of cloud |a.m. p.m.|a.m. p.m.|a.m. p.m.|a.m. p.m.|a.m. p.m.||a.m. p.m.|
--------------+---------+---------+---------+---------+---------++---------+
Cirrus | 6 2 | 15 2 | 9 2 | 5 3 | 6 3 || 41 12 |
Cirro-stratus | -- -- | -- -- | -- -- | -- -- | -- -- || -- -- |
Cirro-cumulus | 4 4 | 7 11 | 3 5 | 6 8 | 17 10 || 37 38 |
Cumulus | 3 4 | 4 7 | 10 9 | 15 13 | 5 13 || 37 46 |
Strato-cumulus| 2 6 | 3 10 | 7 14 | 2 3 | -- 3 || 14 36 |
Stratus | -- -- | -- 1 | -- -- | -- 1 | 1 2 || 2 4 |
Nimbus | -- -- | -- -- | -- -- | -- -- | -- -- || -- -- |
Clear | -- -- | 2 -- | 2 1 | -- -- | 2 -- || 6 1 |
--------------+---------+---------+---------+---------+---------++---------+
UNUSUAL WEATHER PHENOMENA, SANTA LUCIA, 1913-14
[Illustration: Fig. 105--Monthly cloudiness of Santa Lucia from January
to July, 1914. Mean cloudiness for the whole period is also shown.]
The following abstracts are selected because they give some important
features of the weather not included in the preceding tables and graphs.
Of special interest are the strong contrasts between the comparatively
high temperatures of midday and the sudden “tempests” accompanied by
rain or hail that follow the strong convectional movements dependent
upon rapid and unequal heating. The furious winds drive the particles of
hail like shot. It is sometimes impossible to face them and the pack
train must be halted until the storm has passed. Frequently they leave
the ground white with hailstones. We encountered one after another of
these “tempestades” on the divide between Lambrama and Antabamba in
1911. They are among the most impetuous little storms I have ever
experienced. The longest of them raged on the divide from two-o’clock
until dark, though in the valleys the sun was shining. Fortunately, in
this latitude they do not turn into heavy snowstorms as in the
Cordillera of northwestern Argentina, where the passes are now and then
blocked for weeks at a time and loss of human life is no infrequent
occurrence.[35] They do, however, drive the shepherds down from the
highest slopes to the mid-valley pastures and make travel uncomfortable
if not unsafe.
ABSTRACT FROM DAILY WEATHER OBSERVATIONS, SANTA LUCIA, 1913-14
NOVEMBER
“Tempest” recorded 11 times, distant thunder and lightning 9 times.
Unusual weather records: “clear sky, scorching sun, good weather”
(Nov. 29); “morning sky without a single cloud, weather agreeable”
(Nov. 30).
DECEMBER
Clear morning sky 6 times. Starry night or part of night 7 times.
Beginning of rain and strong wind frequently observed at 5-6 P.M.
“Tempest” mentioned 19 times--5 times at midnight, 8 times at 5-6
P.M.
JANUARY
Clear morning sky 5 times. Starry night 3 times. Rain, actual or
threatening, characteristic of afternoons. “Tempest,” generally
about 5-6 P.M., 7 times. Sun described 4 times as scorching and,
when without wind, heat as stifling. Weather once “agreeable.”
FEBRUARY
Constant cloud changes, frequent afternoon or evening rains.
“Tempest,” generally 4 P.M. and later, 16 times.
MARCH
Twice clear morning skies, once starry night. Scorching sun and
stifling heat on one occasion. “Tempest,” generally in late
afternoon and accompanied by hail, 19 times. Observed 3 or 4 times
a strong, “land breeze” (terral) of short duration (15-20 mins.)
and at midnight.
MOROCOCHA
Morococha, in the Department of Ancachs, Peru, lies in 76° 11′ west
longitude and 11° 45′ south latitude and immediately east of the crest
line of the Maritime Cordillera. It is 14,300 feet above sea level, and
is surrounded by mountains that extend from 1,000 to 3,000 feet higher.
The weather records are of special interest in comparison with those of
Santa Lucia. Topographically the situations of the two stations are
closely similar hence we may look for climatic differences dependent on
the latitudinal difference. This is shown in the heavier rainfall of
Morococha, 4° nearer the equatorial climatic zone. (For location see
Fig. 66.)
The meteorological data for 1908-09 were obtained from records kept by
the Morococha Mining Company for use in a projected hydro-electric
installation. Other data covering the years 1906-11 have appeared in the
bulletins of the _Sociedad Geográfica de Lima_. These are not complete
but they have supplied rainfall data for the years 1910-11;[36] those
for 1906 and 1907 have been obtained from the _Boletín de Minas_.[37]
TEMPERATURE
The most striking facts expressed by the various temperature curves are
the shortness of the true winter season--its restriction to June and
July--and its abrupt beginning and end. This is well known to anyone who
has lived from April to October or November at high elevations in the
Central Andes. Winter comes on suddenly and with surprising regularity
from year to year during the last few days of May and early June. In the
last week of July or the first week of August the temperatures make an
equally sudden rise. During 1908 and 1909 the mean temperature reached
the freezing point but once each year--July 24 and July 12
respectively. The absolute minimum for the two years was -22° C. July of
1908 and June of 1909 are also the months of smallest diurnal
variability, showing that the winter temperatures are maintained with
great regularity. Like all tropical high-level stations, Morococha
exhibits winter maxima that are very high as compared with the winter
maxima of the temperate zone. In both June and July of 1908 and 1909 the
maximum was maintained for about a week above 55° F. (12.8° C.), and in
1909 above 60° F. (15.6° C.), the mean maximum for the year being only
4.7° F. higher. For equal periods, however, the maxima fell to levels
about 10° F. below those for the period from December to May, 1908.
It is noteworthy that the lowest maximum for 1909 was in October, 44° F.
(6.7° C.); and that other low maxima but little above those of June and
July occur in almost all the other months of the year. While 1909 was in
this respect an exceptional year, it nevertheless illustrates a fact
that may occur in any month of any year. Its occurrence is generally
associated with cloudiness. One of the best examples of this is found in
the January maximum curve for 1909, where in a few days the maxima fell
12° F. Cloud records are absent, hence a direct comparison cannot be
made, but a comparison of the maximum temperature curve with the graphic
representation of mean monthly rainfall, will emphasize this relation of
temperature and cloudiness. February was the wettest month of both 1908
and 1909. In sympathy with this is the large and sharp drop from the
January level of the maxima--the highest for the year--to the February
level. The mean temperatures are affected to a less degree because the
cloudiness retards night radiation of heat, thus elevating the maxima.
Thus in 1908 the lowest minimum for both January and February was 28.4°
F. (-2° C.). For 1909 the minima for January and February were 27.5° F.
(-2.5° C.) and 29.3° F. (-1.5° C.) respectively.
[Illustration: FIG. 106 A--DIURNAL TEMPERATURE, MOROCOCHA, 1908
B--DIURNAL TEMPERATURE, MOROCOCHA, 1909
D--DIURNAL RANGE OF TEMPERATURE, MOROCOCHA, 1908
E--DIURNAL RANGE OF TEMPERATURE, MOROCOCHA, 1909
G--DIURNAL VARIABILITY OF TEMPERATURE, MOROCOCHA, 1908
H--DIURNAL VARIABILITY OF TEMPERATURE, MOROCOCHA, 1909
C--MEAN MONTHLY TEMPERATURE, MOROCOCHA
F--MONTHLY MEANS OF DIURNAL RANGE OF TEMPERATURE, MOROCOCHA]
The extent to which high minima may hold up the mean temperature is
shown by the fact that the mean monthly temperature for January, 1908,
was lower than for February. Single instances illustrate this relation
equally well. For example, on March 5th, 1908, there occurred the
heaviest rainfall of that year. The maximum and minimum curves almost
touch. The middle of April and late September, 1909, are other
illustrations. The relationship is so striking that I have put the two
curves side by side and have had them drawn to the same scale.
FREQUENCY OF THE DIURNAL VARIABILITY, MOROCOCHA, 1908 AND 1909
1908
-----------------------------------------------------------------
Degrees | | | | | | | | | | | | |Total No.
F. | J.| F.| M.| A.| M.| J.| J.| A.| S.| O.| N.| D.| of days
--------+---+---+---+---+---+---+---+---+---+---+---+---+---------
0 | --| 3 | 2 | 3 | --| --| 2 | 1 | 3 | 1 | 1 | 3 | 19
0-1 | 6 | 5 | 6 |10 | 9 |10 |13 |10 | 8 | 6 | 6 | 5 | 94
1-2 | 4 | 1 | 3 | 7 | 5 | 3 | 7 | 7 | 8 | 6 | 6 | 4 | 61
2-3 | 6 | 1 | 3 | 4 | 9 | 2 | 2 | 4 | 4 | 7 | 7 | 4 | 53
3-4 | 5 | 3 | 2 | 3 | 3 | 4 | 2 | 9 | 4 | 5 | 3 | 5 | 48
4-5 | 2 | 3 | 1 | 1 | 2 | 5 | 5 | --| 1 | 1 | 6 | 3 | 30
Over 5 | 3 | 4 | 3 | 2 | 3 | 6 | --| --| 2 | 5 | 1 | 5 | 34
--------+---+---+---+---+---+---+---+---+---+---+---+---+---------
Days per|26 |20 |20 |30 |31 |30 |31 |31 |30 |31 |30 |20 | 339
month | | | | | | | | | | | | |
------------------------------------------------------------------
1909
---------------------------------------------------------------------
| | | | | | | | | | | | | |Mean
Degrees | | | | | | | | | | | | |Total |for
F. | J.| F.| M.| A.| M.| J.| J.| A.| S.| O.| N.| D.|No. of|1908
| | | | | | | | | | | | | days |-1909
--------+---+---+---+---+---+---+---+---+---+---+---+---+------+-----
0 | 6 | 1 | 4 | 2 | 1 | 2 | 4 | 4 | 3 | 6 | 2 | 1 | 36 | 27.5
0-1 | 9 | 8 | 5 | 6 | 6 | 7 | 8 |13 | 9 | 4 |11 |10 | 96 | 95
1-2 | 4 | 6 | 8 | 3 |11 |14 | 3 | 3 | 5 | 3 | 9 | 6 | 75 | 68
2-3 | 3 | 7 | 4 | 8 | 4 | 3 | 6 | 6 | 4 | 6 | 1 | 3 | 55 | 54
3-4 | 4 | 5 | 3 | 6 | 4 | 4 | 4 | 3 | 6 | 3 | 2 | 5 | 49 | 48.5
4-5 | 1 | 1 | 5 | 1 | 2 | --| 2 | 1 | 1 | 2 | --| 2 | 18 | 24
Over 5 | 4 | --| 2 | 4 | 3 | --| 4 | 1 | 2 | 7 | 5 | 3 | 35 | 34.5
--------+---+---+---+---+---+---+---+---+---+---+---+---+------+-----
Days per|31 |28 |31 |30 |31 |30 |31 |31 |30 |31 |30 |30 | 364 |351.5
month | | | | | | | | | | | | | |
---------------------------------------------------------------------
RAINFALL
The annual rainfall of Morococha is as follows:
1906 28 inches ( 712 mm.)
1907 40 " (1,011 mm.)[38]
1908 57 " (1,450 mm.)
1909 45 " (1,156 mm.)
1910 47 " (1,195 mm.)
1911 25 " ( 622 mm.)
[Illustration: FIG. 107A.]
[Illustration: FIG. 107B.]
[Illustration: FIG. 107C.]
[Illustration: Fig. 107--Rainfall of Morococha. Fig. 107A shows daily
rainfall during the rainy (summer) season, 1908-1909. Fig. 107B shows
monthly rainfall from July, 1905, to December, 1911, and Fig. 107C the
annual and mean rainfall for the same period.]
The mean for the above six years amounts to 40 inches (1,024 mm.). This
is a value considerably higher than that for Caylloma or Santa Lucia.
The greater rainfall of Morococha is probably due in part to its more
northerly situation. An abnormal feature of the rainfall of 1908, the
rainiest year, is the large amount that fell in June. Ordinarily June
and July, the coldest months, are nearly or quite rainless. The normal
concurrence of highest temperatures and greatest precipitation is of
course highly favorable to the plant life of these great altitudes. Full
advantage can be taken of the low summer temperatures if the growing
temperatures are concentrated and are accompanied by abundant rains.
Since low temperatures mean physiologic dryness, whether or not rains
are abundant, the dryness of the winter months has little effect in
restricting the range of Alpine species.
The seasonal distribution of rain helps the plateau people as well as
the plateau plants. The transportation methods are primitive and the
trails mere tracks that follow the natural lines of topography and
drainage. Coca is widely distributed, likewise corn and barley which
grow at higher elevations, and wool must be carried down to the markets
from high-level pastures. In the season of rains the trails are
excessively wet and slippery, the streams are often in flood and the
rains frequent and prolonged. On the other hand the insignificant
showers of the dry or non-growing season permit the various products to
be exchanged over dry trails.
The activities of the plateau people have had a seasonal expression from
early times. Inca chronology counted the beginning of the year from the
middle of May, that is when the dry season was well started and it was
inaugurated with the festivals of the Sun. With the exception of June
when the people were entirely busied in the irrigation of their fields,
each month had its appropriate feasts until January, during which month
and February and March no feasts were held. April, the harvest month,
marked the recommencement of ceremonial observances and a revival of
social life.[39]
In Spanish times the ritualistic festivals, incorporated with fairs,
followed the seasonal movement. Today progress in transportation has
caused the decadence of many of the fairs but others still survive. Thus
two of the most famous fairs of the last century, those of Vilque
(province of Puno) and Yunguyo (province of Chucuito), were held at the
end of May and the middle of August respectively. Copacavana, the famous
shrine on the shores of Titicaca, still has a well-attended August fair
and Huari, in the heart of the Bolivian plateau, has an Easter fair
celebrated throughout the Andes.
COCHABAMBA
Cochabamba, Bolivia, lies 8,000 feet above sea level in a broad basin in
the Eastern Andes. The Cerro de Tunari, on the northwest, has a snow and
ice cover for part of the year. The tropical forests lie only a single
long day’s journey to the northeast. Yet the basin is dry on account of
an eastern front range that keeps out the rain-bearing trade winds. The
Rio Grande has here cut a deep valley by a roundabout course from the
mountains to the plains so that access to the region is over bordering
elevations. The basin is chiefly of structural origin.
The weather records from Cochabamba are very important. I could obtain
none but temperature data and they are complete for 1906 only. Data for
1882-85 were secured by von Boeck[40] and they have been quoted by
Sievers and Hann. The mean annual temperature for 1906 was 61.9° F.
(16.6° C.), a figure in close agreement with von Boeck’s mean of 60.8°
F. (16° C.). The monthly means indicate a level of temperature favorable
to agriculture. The basin is in fact the most fertile and highly
cultivated area of its kind in Bolivia. Bananas, as well as many other
tropical and subtropical plants, grow in the central plaza. The nights
of midwinter are uncomfortably cool; and the days of midsummer are
uncomfortably hot but otherwise the temperatures are delightful. The
absolute extremes for 1906 were 81.5° F. (27.5° C.) on December 11, and
39.9° F. (4.4° C.) on July 15 and 16. The (uncorrected) readings of von
Boeck give a greater range. High minima rather than high maxima
characterize the summer. The curve for 1906 shows the maxima for June
and July cut off strikingly by an abrupt drop of the temperature and
indicates a rather close restriction of the depth of the season to these
two months, which are also those of greatest diurnal range.
[Illustration: FIG. 108 A--DIURNAL TEMPERATURE, COCHABAMBA, 1906
B--DIURNAL TEMPERATURE, COCHABARMBA, 1907
E--DIURNAL RANGE OF TEMPERATURE, COCHABARMBA, 1907
D--DIURNAL RANGE OF TEMPERATURE, COCHABARMBA, 1906
G--DIURNAL VARIABILITY, COCHABARMBA, 1906
H--DIURNAL VARIABILITY, COCHABAMBA, 1907
C--MEAN MONTHLY TEMPERATURES, COCHABAMBA
F--MONTHLY MEANS OF DIURNAL RANGE, COCHABAMBA]
The rainfall of about 18 inches is concentrated in the summer season, 85
per cent falling between November and March. During this time the town
is somewhat isolated by swollen streams and washed out trails: hence
here, as on the plateau, there is a distinct seasonal distribution of
the work of planting, harvesting, moving goods, and even mining, and of
the general commerce of the towns. There is an approach to our winter
season in this respect and in respect of a respite from the almost
continuously high temperatures of summer. The daytime temperatures of
summer are however mitigated by the drainage of cool air from the
surrounding highlands. This, indeed, prolongs the period required for
the maturing of plants, but there are no harmful results because
freezing temperatures are not reached, even in winter.
MONTHLY TEMPERATURES, COCHABAMBA, 1906
-------------+-------------+-------------+-------------+--------------
Month | Mean Min. | Mean Max. | Mean Range | Daily Mean
-------------+-------------+-------------+-------------+--------------
January | 55.7 | 72.25 | 16.65 | 63.3
February | 61.2 | 71.3 | 10.1 | 65.5
March | 59.8 | 72.6 | 12.8 | 65.5
April | 55.06 | 70.8 | 15.74 | 62.2
May | 50.9 | 68.7 | 17.8 | 59.1
June | 47.1 | 65.6 | 18.5 | 55.6
July | 44.8 | 64.9 | 20.1 | 54.1
August | 49.9 | 68.0 | 18.1 | 58.2
September | 55.6 | 73.2 | 17.6 | 63.7
October | 56.1 | 73.4 | 17.3 | 64.0
November | 58.1 | 75.7 | 17.6 | 66.2
December | 58.6 | 73.9 | 15.3 | 65.8
-------------+-------------+-------------+-------------+--------------
[Illustration: FIGS. 109-113--Temperature curves for locations in the
montaña, July and August, 1911. The curves are based on hourly readings
with interpolated readings for such critical occurrences as the
appearance of cloud or rain. Dry bulb readings are shown by solid lines,
wet bulb by dotted lines, and breaks in the continuity of the
observations by heavy broken lines. Fig. 109 is for Pongo de Mainique,
August 20 and 21; Fig. 110 for Yavero; Fig. 111 for Santo Anato, August
11 and 12; Fig. 112 for Sahuayaco, August 20, and Fig. 113 for Santa
Ana, July 30 to August 1.]
[Illustration: FIG. 114--Typical afternoon cloud composition at Santa
Ana during the dry season.]
[Illustration: FIG. 115--Temperature curve for Abancay drawn from data
obtained by hourly readings on September 27, 1911. Dry bulb readings are
shown by a heavy solid line, wet bulb readings by a dotted line. The
heavy broken line shows the normal curve when the sky is unobscured by
cloud. The reduction in temperature with cloud is very marked.]
FREQUENCY OF DIURNAL VARIABILITY AT COCHABAMBA, 1906
-------+----+----+----+----+----+----+----+----+----+----+----+----++------
| | | | | | | | | | | | ||Total
Degrees| | | | | | | | | | | | ||No. of
F. | J. | F. | M. | A. | M. | J. | J. | A. | S. | O. | N. | D. || days
-------+----+----+----+----+----+----+----+----+----+----+----+----++------
0 | 1 | 3 | 10 | 12 | 6 | 10 | 9 | 6 | 9 | 6 | 3 | 4 || 79
0-1 | 5 | -- | 3 | 5 | 3 | 3 | -- | 4 | -- | 3 | 1 | 1 || 28
1-2 | 10 | 10 | 13 | 11 | 15 | 7 | 14 | 11 | 15 | 10 | 14 | 13 || 143
2-3 | 7 | 11 | 3 | 1 | 5 | 8 | 7 | 4 | 3 | 6 | 7 | 6 || 68
3-4 | 6 | 2 | 2 | 1 | 2 | 2 | 1 | 6 | 3 | 4 | 3 | 5 || 37
4-5 | -- | -- | -- | -- | -- | -- | -- | -- | -- | 1 | 1 | 1 || 3
Over 5 | 2 | 2 | -- | -- | -- | -- | -- | -- | -- | 1 | 1 | 1 || 7
-------+----+----+----+----+----+----+----+----+----+----+----+----++------
A series of curves shows the daily march of temperature at various
locations along the seventy-third meridian. Figs. 109 to 113 are for the
Urubamba Valley. Respectively they relate to Pongo de Mainique, 1,200
feet elevation (365 m.), the gateway to the eastern plains; Yavero,
1,600 feet (488 m.), where the tributary of this name enters the main
stream; Santo Anato, 1,900 feet (580 m.); Sahuayaco, 2,400 feet (731
m.), and Santa Ana, 3,400 feet (1,036 m.), one of the outposts of
civilization beyond the Eastern Cordillera. The meteorological
conditions shown are all on the same order. They are typical of dry
season weather on the dry floor of a montaña valley. The smooth curves
of clear days are marked by high mid-day temperatures and great diurnal
range. Santo Anato is a particularly good illustration: the range for
the 24 hours is 38° F. (21.1° C.). This site, too, is remarkable as one
of the most unhealthful of the entire valley. The walls of the valley
here make a sharp turn and free ventilation of the valley is obstructed.
During the wet season tertian fever prevails to a degree little known
east of the Cordillera, though notorious enough in the deep valleys of
the plateau. The curves show relative humidity falling to a very low
minimum on clear days. At Santo Anato and Santa Ana, for example, it
drops below 30 per cent during the heat of the day. Afternoon
cloudiness, however, is a common feature even of the dry season. A
typical afternoon cloud formation is shown in Fig. 114. The effect on
temperature is most marked. It is well shown in the curve for August 20
and 22 at Yavero. Cloudiness and precipitation increase during the
summer months. At Santa Ana the rainfall for the year 1894-95 amounted
to 50 inches, of which 60 per cent fell between December and March. For
a discussion of topographic features that have some highly interesting
climatic effects in the eastern valleys of Peru see Chapter VI.
[Illustration: FIGS. 116-118--Temperature curves for locations in the
Maritime Cordillera and its western valleys, October, 1911. For
construction of curves see Figs. 109-113. Fig. 116 is for Camp 13 on the
northern slope of the Maritime Cordillera (which here runs from east to
west), October 13-15; Fig. 117 for Cotahuasi, October 26; Fig. 118 for
Salamanca, October 31.]
[Illustration: FIG. 119.
FIG. 120.
FIGS. 119-120--Temperature curves for the Coast Desert, November, 1911.
Fig. 119 is for Aplao, November 4 and 5; and Fig. 120 for Camaná,
November 9 and 10. For construction of curves see Figs. 109 to 113.]
Abancay, 8,000 feet (2,440 m.), in one of the inter-Andean basins, is
situated in the zone of marked seasonal precipitation. The single day’s
record shows the characteristic effect of cloud reducing the maximum
temperature of the day and maintaining the relative humidity.