HOW THE FORESTS FEED THE CLOUDS 

 BY RAPHAEL ZON, F. E. 



Forest Economist, United States Forest Service 



KR a long time it has been accepted without any 

 icstion that all the vapour that is condensed 

 ... the form of rain or snow over the land surface 

 is furnished by the evaporation of water from the 

 oceans. The part which vapour from the ocean plays 

 in the precipitation over the land has been greatly exag- 

 gerated. A noted European meteorologist, Professor 

 Bruckner, has computed the amount of water evapo- 

 rated from the ocean surface and the land surface, and 

 the amount of water which is returned to the ocean and 

 the land in the form of precipitation. The balance 

 sheet of the circulation of water on the earth's surface 

 is shown in the accompanying illustration. The regions 

 tributary to oceans are capable of supplying seven 

 ninths of the precipitation by evaporation from their 

 own areas. The moisture which is carried by the winds 

 into the interior of vast continents, coming thousands of 

 miles from the oceans, is almost exclusively due to con- 

 tinental vapours and not to evaporation from the ocean. 

 Bruckner's figures for the entire earth's surface are 

 corroborated also by study of specific drainage areas. 

 The most interesting study in this direction is that by 

 Professors Francis N. Nipher and George A. Lindsay on 



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