48 



e. a. McGregor 



activities in the Imperial Valley we have heard an often repeated 

 assertion, namely, that the humidity of the region is influenced 

 directly by the use of water in irrigation. We resolved some 

 time ago to accumulate the data necessary to test the validity of 

 this idea, and the present deductions are based on the daily hu- 

 midity readings over a period of three years together with the 

 figures of the Imperial Irrigation District for the total use of 

 water in the Imperial Valley by months for the identical period. 

 Each year in August in the Imperial Valley one hears frequent 

 expressions concerning the alleged high relative humidity con- 

 current with the extreme temperatures at that time. It seems 



TABLE 2 



Use of water in Imperial Valley, January, 1916, to December, 1918, inclusive 



Second Feet 



to have been the almost universal opinion among valley residents 

 that a wave of humidity strikes the region during the month of 

 August. It is also the general belief that the maximum humidity 

 is directly attributable to the great amount of water being used 

 for irrigation at that time. A study of table 1 and fig. 1 will 

 be of interest in this connection. 



It will be noted in table 1 that a three-year average shows that 

 the time of greatest humidity is in August, with the month of 

 December a very close second. 



Similarly, from table 2 it is seen that for the simultaneous 

 three-year period the use of water in irrigating is heaviest during 

 the month of July. 



