226 MISCELLANEOUS FARM SUBJECTS 



does not follow that it is the best method for all dry-farming sections 

 or that it will always give the best returns. In dry-farming sections 

 where the rainfall is not so limited as in Utah, and especially in 

 regions having a summer rainfall, other methods give as good or 

 better returns. 



Importance of Knowing the Normal Rainfall. The rainfall in 

 all parts of the United States is subject to wide fluctuations from year 

 to year. The West does not appear to be more subject to these 

 changes than the East, but the fluctuations are felt more by the dry 

 farmers because they are working upon a closer margin. Crops in 

 the East are often lost through drought and not infrequently under 

 conditions where the up-to-date dry farmer would have produced a 

 good crop. On account, then, of the fluctuations in rainfall in any 

 locality from year to year, it is necessary in judging the rainfall of 

 a region to know the average annual rainfall, or, as it is called, 

 the normal rainfall. This is the only safe basis upon which the 

 rainfall of any region can be judged, and the longer the records the 

 greater is the dependence that can be placed upon the normal. While 

 two years' or three years' observations are safer than a single year's 

 records, it is not uncommon for two or three wet years or for two 

 or three dry years to follow one another in succession, so that the 

 yearly rainfall obtained at such times would be too high or too low. 

 Records for at least five years, and preferably for ten years, are neces- 

 sary to obtain the normal rainfall of a region, and the longer the 

 records the more reliable will be the result obtained. 



In studying the rainfall of a region too much dependence must 

 not be placed upon the records of a single station, especially if this 

 station is located in a mountainous region. Under such conditions 

 marked differences in the annual rainfall are often found between 

 stations located on the highlands and those in the valleys. The cool- 

 ing of the moisture-laden air through expansion as it rises over a 

 range of hills causes precipitation, so that the windward sides of 

 mountains have a greater rainfall than the leeward sides. This is 

 well illustrated in the very heavy rains which occur all along the 

 west slope of the Cascade Range in Washington, Oregon, and north- 

 ern California, while the rainfall on the east side is very much less. 

 This is also well illustrated in Riverside and San Bernardino coun- 

 ties in southern California, where a great change in rainfall occurs 

 as we go eastward a few miles. 



These sudden changes in normal rainfall are not, however, 

 confined to the mountainous regions ; marked instances of this kind 

 occur in the Great Plains, w r here changes in elevation are compara- 

 tively slight. For example, the rainfall in the district around Aber- 

 deen, in Brown County, S. Dak., is nearly 5 inches above that of 

 the surrounding section. This difference is based upon observations 

 extending over twenty years or more ; and the effect upon the crops 

 has been so marked that the farmers generally recognize that good 

 crops may be found in this section when the surrounding regions 

 are suffering from drought. 



