12 



BULLETIN 698^ U. S. DEPARTMEJSTT OP AGRICULTURE. 



LOCAL VARIATION IN PRECIPITATION. 



Much, of the summer rainfall is derived from storms which are very- 

 local in extent. In a single storm period a series of heavy showers 

 may occur at about the same time in the same district but covering 

 different localities and leaving intervening stretches almost unwatered. 



The variation in the rainfall at two near-by points is illustrated in 

 Table III. This table compares the rainfall measured at the United 

 States Weather Bureau observatory in the town of AmariUo with 

 that recorded at the AmariUo Cereal Field Station during seven sum- 

 mer months in the years 1909 and 1914. The distance between the 

 two points of observation is about 2^ miles. , 



Table III.- — Comparison of the rainfall, in inches, at the United States Weather Bureau 

 observatory and at the AmariUo Cereal Field Station during the seven months from 

 March to September, inclusive, in 1909 and 1914- 



Station. 



Mar. 



Apr. 



May. 



Jime. 



July. 



Aug. 



Sept. 



Total. 



Season of 1909: 



1.28 

 1.08 



.15 



.02 



0.50 



.27 



.95 

 1.27 



1.08 

 1.13 



4.43 

 3.83 



4.72 

 5.90 



.84 

 .65 



3.63 

 2.19 



3.07 

 L90 



0.87 

 1.39 



2.97 

 2.52 



2.19 

 1.90 



1.07 

 1.10 



14.27 



Cereal field station 



13.86 



Season of 1914: 



United States Weather Bureau 



13.48 



Cereal field station 



11.29 







These local rains frequently last but a short time, but are of a 

 torrential nature. This often results in a loss of much water by run- 

 off. Such beating rains also puddle the surface soil and cause much 



damage in that way. 



Humidity. 



The atmospheric humidity is low, on the average. This no doubt 



plays an important part in influencing transpiration from growing 



crops. 



Wind. 



Monthly data on wind are shown with other climatic data in Table 

 IV. The average hourly wind velocity in the 10 years from 1907 to 

 1916, inclusive, is 11.8 miles. During the 4-year period from 1907 

 to 1910, inclusive, there was an average of 14 days in each year in 

 which a wind velocity of over 40 miles an hour was recorded. The 

 maximum, 63 miles, occurred on March 24, 1909. During the 6-year 

 period from 1911 to 1916, inclusive, the data show merely the max- 

 imum hourly velocity recorded during the month and no longer the 

 number of days having high wind velocities. The maximum, 46 

 miles an hour, occurred in February and April, 1911, and in April, 

 1915. Such high winds often cause great damage to the crops 

 either by covering up the young plants, by cutting them off by moving 

 particles of soil, or by blowing down the crop when it is almost or 

 quite mature. 



