The precipitation records of Monterrey and its neighborhood are very
meager, and cannot be relied on for a longer period than from 1894 to
1909, inclusive. The records are available from 1886, but in the early
years there are many apparent discrepancies, and they are probably
inaccurate. The average rainfall for the 15 years (1894-1908) is 21.94
in.; the driest years for this period are as follows: 1894, 14.14 in.;
1902, 15.29 in.; 1907, 15.23 in.; 1908, 15.11 in. Assuming the early
records to be correct, the average rainfall for the period, 1886-1908,
would be 19.86 in.
At Saltillo, which is 50 miles due southwest, at an elevation of about
1,520 m. above sea level, the average rainfall for the 23 years,
1884-1908, inclusive, is given as 21 in. The maximum year was 1889, with
33-1/2 in., and the minimum 1903, with 7-1/2 in.
At Carmen, in the State of Tamaulipas, 144 km. southwest of Monterrey,
at an elevation of about 310 m. above sea level, the average fall for 12
years is 24.70 in., the maximum year being 1897, with a fall of 34.09
in., and the minimum year, 1905, with 13.41 in.
[Illustration: FIG. 1.--ANNUAL RAINFALL IN MONTERREY COVERING THE PERIOD
FROM 1894 TO 1909.]
Fig. 1 shows the annual variation of rainfall at Monterrey for
1894-1909. Fig. 2 shows the monthly variation during the same period,
and gives the minimum, average, and maximum for each month.
From these diagrams it will be seen that the months of least rainfall
are December, January, February, and March, with averages of 0.66, 0.59,
0.79, and 0.93 in., respectively. The months of greatest rainfall are
August, with an average of 4.39 in., and September with 4.87 in. The
maximum in any month prior to 1909 was 16.75 in., during September,
1904.
_Rainfall in 1909._--The rainfall in 1909 was unprecedented, causing the
disastrous flood in the Santa Catarina River, which will be referred to
when describing the works. Fig. 3 shows the monthly rainfall for 1906 to
1909, inclusive, and has been plotted to show the variation of rainfall
prior to the great precipitation of August, 1909. In that month there
were two heavy falls, one beginning at midnight on August 9th, and
during the following 42 hours a fall of 13.28 in. was recorded by the
gauge at the Water-Works Company's general offices, 10.20 in. of which
fell, during the first 24 hours. From 6 P. M. to 11 P. M., on August
10th, 5.019 in. were recorded, or an average of 1 in. per hour.
[Illustration: FIG. 2.--MONTHLY RAINFALL IN MONTERREY COVERING THE
PERIOD FROM 1894 TO 1909 INCLUSIVE.]
[Illustration: FIG. 3.--MONTHLY VARIATION OF RAINFALL AT MONTERREY
1906-1907-1908-1909.]
After 13 dry days, another rainstorm began, at 4 P. M., on August 25th,
and continued more or less intermittently until August 29th. During this
98-hour period there was an additional fall of 21.61 in., 11.27 in.
falling in 24 hours.
The total precipitation during the month amounted to 36.00 in. The
highest previous record for the month of August was in 1895, with a fall
of 6.61 in. Fig. 4 gives the details of the two heavy precipitations in
August. As no automatic recording gauge was available, the maximum
intensity could only be computed approximately, owing to the
intermittent character of the readings taken from the ordinary rain
gauge on the roof of the Water-Works Company's office in the city. From
the readings thus obtained, it was shown that the maximum intensity
occurred early on the morning of the 28th, and was nearly 2 in. per
hour. Above Monterrey, in the Santa Catarina water-shed, it is believed
that the precipitation was considerably greater, but no gauges were
accessible during the month.
[Illustration: FIG. 4.--CURVE OF RAINFALL AT MONTERREY DURING AUGUST
10TH & 11TH AND FROM AUGUST 25TH TO 29TH - 1909.]
The total rainfall for 1909 amounted to 47.46 in., of which 75% fell in
August. This is 50% greater than the previous highest annual record
(31.65 in. in 1900) for Monterrey.
_Temperature._--Fig. 6 gives a record of the temperature at Monterrey
from 1901 to 1909, inclusive. These records were taken at an altitude of
520 m. It will be noted that the lowest recorded temperatures are in
January and February. The lowest during these years was 24 deg. Fahr., in
January, 1905. The monthly maxima vary between 80 and 110 deg. Fahr. The
mean annual temperature is 72.65 deg. Fahr. (The mean annual barometer is
28.2 in.)
[Illustration: FIG. 6.--DIAGRAM OF TEMPERATURE VARIATION AT MONTERREY,
1901-09.]