EVAPOEATION IN DRY-FARMING SECTIONS. 



19 



Table I. — Evaporation from a tank during the six summer months from April to 

 September, inclusive, at various points in the United States — Continued. 



State. 



Ohio 



South Dakota. 



Texas 



Utah 



Washington 

 Wisconsin. . 



Wyoming. 



a Report Chief of Engineers, U. S. Army, 1808, p. 978. 



b Report Irrigation Investigations, Office of Experiment Stations, 1901, p. 31 (May 18 to November 9). 

 (The records for Prosser are for 1900, May 9 to October 29, and 1901, April 22 to October 28.) 

 c Water-Supply Papers, No. 7, p. 20. 

 dUtah Agricultural College Bulletin 80, 1901, p. 77. 

 e Report Chief of Engineers, U. S. Army. 1868, p. 978. 



/Report Irrigation Investigations, Office of Experiment Stations, 1901, p. 335 (estimated from 3 months' 

 records). 



g Report Irrigation Investigations, Office of Experiment Stations, 1902, p. 232 (estimated from 4 months' 

 records). 



A For records 1893 to 1898, inclusive, see Water-Supply Papers, No. 81, p. 21. 



1893 37.1 inches (estimated from records April 24 to September 30). 



1894 38.5 inches (estimated from records April 26 to September 30). 



1895 37.1 inches (estimated from records April 17 to September 30). 



1896 40.5 inches (estimated from records June 1 to September 30). 



1897 42.0 inches (estimated from records April 24 to September 30). 



1898 42.3 inches (estimated from records April 15 to September 30). 



For records ol 1901, see Wyoming Agricultural Experiment Station Bulletin 52, p. 50. 



1901 38.2 (estimated from records May 9 to September 30). 



The rate of evaporation from a wet soil surface is about the same 

 as from a freely exposed water surface in a tank. a Consequently, if 

 the surface of the soil were kept constantly wet the evaporation from 

 the soil would be approximately equal to that found by means of the 

 tank. The fact that we find the evaporation as measured by the 

 tank to be so much greater than the rainfall shows how efficient our 

 methods of cultivation must be in order that we may have any water 

 at all left for the use of the crop. In a region having an evaporation 

 during the six summer months of 45 inches and a rainfall of 18 inches, 

 most of which occurs during the summer, we are able through culti- 

 vation to cut the evaporation from the soil down to approximately 



a This statement must, of course, be, considered as only approximate. Very wet, 

 dark-colored soils fre ?ly exposed in the sun will usually lose water by evaporation 

 more rapidly than a free water surface, since the dark soil surface absorbs a larger pro- 

 portion of the energy frjm the sun than the free water surface does. The evaporation 

 from light-colored soils when wet agrees more closely with that taking place from a 

 free water surface of equal area. As the soils dry out the rate of evaporation gradu- 

 ally decreases. This shows the advantage in using a clean, freely exposed water sur- 

 face in measuring evaporation, which avoids the errors arising from changes in the 

 nature of the evaporating surface. 

 188 



City or town. 



Cleveland 



Bellefourche 



Highmore 



Amarillo 



Dal hart 



San Antonio. 



Corinne 



Fort Douglas. 



Logan 



Nephi 



Prosser 



Milwaukee... 

 Stevens Point 



Laramie 



Num- 

 ber of 

 years 



Date. 



1802 to 1807, inclusive 



1908 to 1909, inclusive 



1907.. 



1907 to 1909, inclusive 



1908 to 1909, inclusive 



1907 to 1909, inclusive 



1901 



1890-1-2 



1901 



1908 to 1909, inclusive 



1900 24.6 



1901 30.6 



1863 to 1867 



1901 J 28.2 



1902 29. 4 



1893-1898, 1901 



Evapora- 

 tion. 



a 24. 6 

 38.0 

 33.7 

 52.4 

 54.6 

 45.7 

 6 40.1 

 <30.7 

 d34.3 

 42.0 

 6 27.6 

 e 26. 9 

 28.8 

 h 39. 4 



