HUMIDITY IN A RECLAIMED DESERT 



49 



Figure 1 presents a graph visualizing the relation of the 

 humidity to the use of water. 1 At a glance one is struck by the 

 almost complete lack of correlation between humidity and irriga- 

 tion. In January the use of water is at its lowest ebb, whereas 

 the humidity of the atmosphere is almost at its maximum. 

 Through February, March, April and May the use of water rap- 

 idly increases until the amount distributed over the valley in 

 May is over four times that of January. Concurrent, however, 

 with this greatly increased use of water it is noted that the hu- 

 midity decreases fully as rapidly — from 46.4 per cent in January 

 to 25.0 per cent in May. From May to the end of July there is a 



20% 



JAN. 



JON. 



JUL. 



Fig. 1. Graphs showing the relation between humidity and irrigation in the 

 Imperial Valley. Relative humidity (heavy line), three-year average, 1916-1918; 

 use of water in thousand second-feet (light line), three year average for seasons 

 of 1916-1918. 



slight increase in the use of water amounting to about 18 per 

 cent of the May volume. However, during the same period there 

 is a remarkably disproportionate enhancement of humidity, 

 amounting in July to 88 per cent in excess of the May humidity 

 per cent. Furthermore, for our three-year period under con- 

 sideration, the crest of the seasonal humidity curve was reached 



1 The humidity readings were made at El Centro with the regulation Weather 

 Bureau sling psychxometer checked by readings on a drum hydrothermograph. 

 The data for the use of water were furnished from the files of the Imperial 

 Irrigation District which has complete control of all water used for irrigation 

 in the Imperial Valley of California and Mexico. 



