BULLETIN 222, U. S. DEPARTMENT OP AGRICULTURE. 



CLIMATIC CONDITIONS. 



The climate of the Great Plains has been classified as semiarid. 

 It may be better to say that it is changeable, varying from season 

 to season from almost humid to almost arid, with a relatively low 

 mean annual precipitation. Years of relatively high precipitation 



may be followed by 



years of relatively 

 low precipitation. 

 Other climatic factors 

 usually correspond to 

 the rainfall. A year 

 of relatively high rain- 

 fall will have a lower 

 rate of evaporation 

 and higher relative 

 humidity than will be 

 found in the unfavor- 

 able years. 



Another climatic 

 factor of much im- 

 portance in crop pro- 

 duction on the Plains 

 is the distribution of 

 the rainfall, which 

 within certain limits 

 is more important 

 than the tot al 

 amount. A relatively 

 low rainfall properly 

 distributed may pro- 

 duce a crop where a 

 much higher rainfall 

 coming with unfavor- 

 able distribution may 

 result in a crop fail- 

 ure, each starting with 

 the same amount of 

 available water in the 

 soil. A vast difference in crop yields usually results from a soil that 

 starts out in the spring with a small amount of stored moisture and 

 one that is well supplied with moisture. 



Space in this bulletin will not allow a full description or record of 

 the climatic conditions at the various stations during the time cov- 

 ered by these investigations. These records are published by the 

 United States Weather Bureau. 



Fig. 1.— Sketch map of the Great Plains area, -which includes parts 

 of ten States and consists of about 400,000 square miles of territory. 

 Its western boundary is indicated by the 5,000-foot contour. The 

 location of each field station within the area is shown by a dot 

 Within a circle (©). 



