BULLETIN 222, U. S. DEPARTMENT OF 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 total 
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 (©). 
