46 Gen. A.W.Greely — Rainfall Types of the United States. 



dental occurrence. It confines itself to a question of great and 

 sometimes vital importance, to the characteristic distribution of 

 13recipitation throughout the year, and, as is believed, presents 

 a successful analysis of the average fluctuations from month to 

 month, so that for the first time a satisfactory presentation is 

 possible of all the simj^le rainfall types and of most of the 

 composite tyjDes which obtain over the broad expanse of the 

 inhabited portions of North America. 



The necessity of careful and scientific study of climatic condi- 

 tions in connection with prospective enterprises, whether per- 

 taining to agriculture, commerce, navigation, or to special indus- 

 tries, has become obvious the past few years through the spur 

 of competition. Among such conditions, this of rainfall dis- 

 tribution throughout the year is one of the most important. 

 With relation to agriculture, it is essential to know whether pre- 

 cipitation comes at such seasons as to be a benefit or a detriment 

 to the jiroposed crop. In the initiation of irrigation enterprises 

 not only are the questions of guarding against extensive and 

 torrential rainfalls on one hand and of tiding over temporary 

 droughts on the other of importance, but, further, whether the 

 most copious precipitation occurs in such months as to afford 

 water at seasonable periods, or the rain comes at such times that 

 it must be stored for many months with consequent loss from 

 seepage and evaporation. Similarly, this question of distribu- 

 tion of rain throughout the year affects most potently other busi- 

 ness interests of importance. 



That these questions are of current and practical value is 

 evident to every thoughtful man, and that their earlier elucida- 

 tion and the publication of results would have been an extended 

 benefit cannot be questioned. Take agriculture, for instance, 

 which in eastern Colorado is pursued under difficult conditions 

 wherever irrigation is impracticable. Failure of crops very 

 frequently resulted until observation showed that a scanty rain- 

 fall in June is the rule in that section, and that by planting at a 

 certain season the injurious effects of the June drought could be 

 mitigated. 



Nor is the necessity of a definite and accurate determination 

 of the typical forms of annual precipitation in the eastern part 

 of the United tStates less obvious, since the latest text-book on 

 meteorology in use in the United States, that of Loomis, contains 

 the statement that " Throuo'hout most of the United States east 



