16 BULLETIN 1031, U. S. DEPARTMENT OF AGRICULTURE. 
period, 1889 to 1892, inclusive, with approximately average years 
back to 1886 is also shown in figure 2, and further records from the 
El] Paso Station show exceptional precipitation in 1880 and 1884. 
Further analysis of the precipitation data shows that for the 
years 1889 to 1892 the average annual precipitation was 34.1 per cent 
below the mean for the period 1886 to 1919; for 1899 to 1903 the 
departure below mean was 21.5 per cent; for 1908 to 1910, 34.6 
per cent; and for 1916 to 1918, 10.9 per cent. During these same 
periods the average for the season July, August, and September 
was below the mean for these months for the whole period, 1886 to 
1919, by 42.1 per cent in 1889 to 1892; 14.9 per cent in 1899 to 1908; 
28.9 per cent in 1908 to 1910; and 22.8 per cent in 1916 to 1918. 
Over 50 per cent of the mean annual precipitation falls during 
July, August, and September, and since the bulk of the range forage 
is produced primarily by perennial grasses which make their main 
growth during these months, it is not improbable that departure 
from mean precipitation for this growing season has a greater pro- 
portionate effect on the volume of forage produced and upon range 
maintenance than departure from mean annual precipitation. The 
effect of deficient precipitation during this period on the vegetation 
on the Jornada Range Reserve as later brought out seems to war- 
rant this assumption. 
For the present the main tentative deduction which seems war- 
ranted is that in cycles of 8 to 10 years there may occur 3 to 4 con- 
secutive years during which precipitation is enough below the mean 
for the period to result in conditions considered by stockmen as 
drought. If future investigations can more definitely define the 
occurrence, duration, and intensity of these drought pericds and the 
influence of seasonal precipitation, a big fundamental step will be 
made toward possible elimination of hazard connected with live- 
stock production in this region. 
PRECIPITATION ON THE JORNADA RANGE RESERVE. 
Table 4 shows the precipitation by months, from 1914 to 1919, 
inclusive, with the exception of some data lacking in 1914 and 1915, 
for one station located at the headquarters ranch on the Jornada 
Range Reserve. Although rainfall in 1916 was slightly above the 
average for the year, there was a deficiency of 2.17 inches or 45.6 
per cent departure from the average amount received during July, 
August, and September, the main growing season. The heavy rain- 
fall occurring in October was too late for much benefit. During 
1917 not only seasonal but annual precipitation as well was very de- 
ficient. In 1918 the amount of precipitation for the period of July, 
August, and September was not greatly below average for the region, 
( 
