12 DRY FARMING IN RELATION TO RAINFALL AND EVAPORATION. 



Those areas which are included between the 10-inch and 20-inch 

 lines of annual rainfall serve, then, to represent in a general way the 

 dry-farming areas of the United States so far as they may be denned 

 through rainfall. It must be constantly borne in mind, however, 

 that conditions are more severe in the southern part of the region 

 than in the northern part, owing to the high temperature and greater 

 evaporation; so that regions having the same rainfall are by no 

 means equally well adapted to the production of crops. 



COMPARISON OF THE MONTHLY DISTRIBUTION OF RAINFALL IN 

 THE GREAT PLAINS, INTERMOUNTAIN, AND PACIFIC COAST 

 REGIONS. 



The monthly distribution of the rainfall in the western United 

 States can be divided roughly into three types — the summer rainfall 



PAC/F/C. 



/A/TEPMOC/A/T/I//V. 



GP£AT PLA/A/S. 



DALLES, OREGON 



B/SMARCK, NO. 



BO/SE, /DAHO. 



Hi 



Will 



SACRAMENTO, CAL 

 I 



"Ml 



rmi mi 



LOS ANGELES, CAL. 



1 1 111 



mi rm 



■i 



OGDEN, UTAH. 



HUP 



iinimuy 



INTIIII 



PA ROWAN, UTAH. 



U 



a 















..I 



llll 





NORTH PL A TTE, NEB. 



m 



nun 1 1 1 1 mini 

 ■mi il 1 1 1 hi - 



AMAR/LLO, TEX. 







ti 





II 1 

 III 





Fig. 2.— Chart showing the monthly distribution of the rainfall at representative stations in the Great 

 Plains, Intermountain, and Pacific coast regions. The length of the black lines in each diagram rep- 

 resents the monthly precipitation at that place, beginning with January on the left. The scale in 

 inches given on the right of each diagram can be used to find the actual amount of the monthly rainfall. 

 For example, the average monthly rainfall at Bismarck, N. Dak., for June is seen to be inches, while 

 for July it is only a little more than 2 inches. It will be noted that in the Pacific coast region the rain 

 comes principally during the first and last months of the year, that is, in the winter, while in the Great 

 Plains the rain comes principally during the middle of the year, that is, in the summer months. 



of the Great Plains, the winter and spring rainfall of the Inter- 

 mountain district, and the winter rainfall of the Pacific coast region. 

 These three types are illustrated in figure 2, which shows the monthly 

 rainfall for three stations in each of these regions. It will be noted 

 that for Bismarck, N. Dak., North Platte, Nebr., and Amarillo, Tex., 

 which are typical Great Plains stations, the rain occurs principally 

 during the months of June, July, and August, and that the winter 



188 



