CLIMATOLOGY 



79 



followed by warm weather and strong winds, evaporation 

 is very rapid. Frequently the records will indicate a heavy 

 rainfall and high evaporation in the same twenty-four 

 hours. At other times, however, the rainstorm is followed 

 by a low temperature without any wind, and as a result the 

 evaporation is very light. Where the surface is covered 

 with a thick, growing crop which prevents the free circu- 

 lation of air, evaporation may be prevented almost entirely, 

 and several days may pass without the removal of water by 

 this method. 



Table Showing the Monthly Rainfall and Evaporation from 



Water Surfaces through the Growing Months at 



Fargo, North Dakota, in the Years 1902-1905* 



(Note that the monthly evaporation is practically double the rain- 

 fall.) 



Sep- 

 tember 



Average monthly evaporation 



Average monthly rainfall 



Excess of average monthly evapora- 

 tion over rainfall 



Average daily evaporation 



Average daily rainfall 



Excess of average daily evaporation 

 over rainfall 



Inches 



3 -430 

 3.290 



. 140 

 .114 

 .110 



.004 



♦After John T. Stewart, Bulletin iSg, O. E. S., United States Department of 

 Agriculture. 



During August, 1905, in the valley of the Red River of 

 the North, a heavy rain occurred on Monday, followed by 

 several lighter rains and another heavy rain on Thursday. 

 The wheat crop was ripening and was ready to cut. As the 

 soil of that region is very heavy and permits only a limited 

 amount of absorption and percolation and the surface is 

 comparatively level and at that time had few natural or 

 artificial water channels, evaporation was the only agency 

 that could remove the rainfall. Where the surface of the 

 land was exposed to the sun and wind, evaporation took 

 place quickly, but in the wet fields the rank growth oir the 



