10 DRY FARMING IN RELATION TO RAINFALL AND EVAPORATION. 



THE DISTRIBUTION OF THE ANNUAL RAINFALL IN DRY-FARMING 



REGIONS. 



The accompanying chart (fig. 1) shows the annual rainfall in the 

 western United States, and has been prepared by the writers with 

 particular reference to dry-farming regions. a The region repre- 



Fig. 1.— Chart showing the distribution of the annual rainfall in the dry-farming sections of the United 



States. 



sented in the chart has been divided into zones, the boundaries of the 

 zones being represented by lines along which the rainfall is uniform. 

 For example, the heavy curved line marked 20, starting in the north- 



a This chart is based upon the state rainfall maps (see pp. 33 to 45), which include 

 the available rainfall records of the Weather Bureau to January, 1910. 



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