4o8 



REPORT OF THE COMMISSIONERS OF 



floods. The contrary view, that forests not only do not increase precipitation, but 

 that they are without effect on rate of run-off, and hence that floods are quite as great 

 from forested as from deforested areas, has been strongly championed. 



The author has no desire to question the good intentions of the gentlemen 

 presenting the views referred to. He recognizes that the chief difficulty with some of 

 the recent writers on this subject — especially the authors of popular articles in the 

 magazines — has been an evident lack of full acquaintance with the physical data 

 really applying. One object of the present discussion is to some extent supply this 

 lack by actually quoting these data, or, when too extended for citation, to indicate 

 where some of the more important may be found. 



The author does, however, wish to point out as a tentative proposition, that the 

 real reason why forested areas furnish more water in the streams for a given rainfall 

 than do deforested and cultivated areas, is because forests, on the whole, consume less 

 water than do deforested and cultivated areas. The data herein given are especially 

 directed toward establishing this tentative proposition. 



DIVISIONS OF THE SUBJECT. 



We may discuss the subject under the main divisions, Rainfall, Temperature, 

 Hygrometry, Evaporation and Forest Data and the Relation Between Rainfall and 

 Run-off. This division is necessarily taken somewhat arbitrarily, one frequently 

 running into another, and is made merely for the purpose of assisting somewhat in 

 handling the data. 



Before proceeding to the main discussion, the author may very properly indicate 

 that while, as a tentative proposition, he has no doubt that, other conditions remaining 

 the same, forest areas yield more water from a given rainfall than do similar deforested 

 areas — and certain data derived from recent studies in the State of New York will be 

 presented strongly substantiating this view — nevertheless, it is recognized that 

 some of the information really needed for final conclusions, is not yet gathered, and in 

 consequence all final conclusions are necessarily delayed for many years — at any rate 

 so far as the comparison of broad areas widely separated is concerned. Illustrations 

 of why this is true will be given further on. 



The foregoing definition of what seems to the author to be the present state of the 

 data of the stream flow in relation to forests, is made necessary because one of the 

 mooted questions at the present time is as to the proper method of investigation to be 

 pursued. The foreign studies of forest meteorology have been mostly carried on with 

 reference to comparing temperature, hygrometric and other meteorological conditions 

 in the forest, with outside conditions, the run-off of streams having been, generally 

 speaking, only casually considered. 



