16 BULLETIN 1031, U. S. DEPARTMEl^T 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 1903; 

 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 Eange 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 periods 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 EANGE 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. 



