Definition of Rainfall Types. 47 



of the Rocky mountains the rain is pretty equally distributed 

 through the different months of the year, but the rain of sum- 

 mer is everyiohere somewhat greater than that of winter, including 

 melted snow." 



In reality the whole section of country, about 200,000 square 

 miles in extent, dominated by the Tennessee type of rainfall 

 experiences a larger precipitation in winter than in summer, the 

 excess averaging in northern Alabama and southern Kentucky 

 about 10 per cent, in western Georgia and in Tennessee over 

 20 per cent, and in southeastern Arkansas and northern Louisiana 

 from 40 to 50 jDcr cent (plate 20). 



I have pointed out elsewhere the vital importance of a favor- 

 able distribution of rainfall to certain sections of the country, 

 where this favoring type of precipitation has proved to be one 

 of the great bases on which rests the national prosperity of this 

 great republic. Allusion is made to the great grain-producing 

 sections throughout the water- sheds of the upper Mississippi, the 

 Missouri, the Red river of the North, comprising the Dakotas, 

 Minnesota, Kansas, Nebraska, Iowa, Missouri, Wisconsin and 

 Illinois. Over the greater part of this immense area the annual 

 rainfall is very materially less than that of the regions to the 

 eastAvard or southward, b^it, most fortunately for the country, 

 about three-fifths of the rainfall for the entire year occurs oppor- 

 tunely through the period when it is most beneficial to crops, 

 from April to July, inclusive. A less favorable type of rainfall, 

 the Mexican or the Saint LaAvrence, for example, Avould render 

 groAving of grain unprofitable throughout the Avhole of this 

 favored region. 



It remains to briefly indicate the fcAV types of simple rainfall 

 Avith the localities to which they refer, and to the composite 

 types occurring through the OA^erlapj^ing and interference of 

 simple types. 



Composite types must prevail AAdiere tAvo simjDle types are not 

 separated by high mountain ranges, and thus gradually shade 

 or merge into each other. One dividing line, the Rocky moun- 

 tain range, separates by its crest, if not absolutely, yet quite 

 sharply and definitely, the Missouri type in Montana and 

 Wyoming from the Pacific type in Idaho and Washington. 



The term mniple has been applied to those rainftill types Avhich 

 can be graphically expressed by a curve Avith a single bend or 

 inflection. The average monthly amounts pass from the single 



