HYDROLOGY OF NEW YORK 



81 



therefore, that a forest-protected area will show less evaporation 

 during the months of the storage period than will an area which 

 is fully exposed to the sweep of the winds. In proof of this it 

 may be cited that the Hudson area shows, on an average, only 4.6 

 inches evaporation during the storage period, while the Genesee 

 area, during the same period, shows 8.9 inches. The Croton area 

 shows 6.85 inches evaporation for the same period. It is probable 

 that, due to greater elevation, winds are more searching on the 

 Genesee area than on the Croton area, although the forestation is 

 not very different. It is also probable that owing to proximity to 

 the ocean the humidity is greater on the Croton area than on 

 the Genesee, but since there are no observations this latter point 

 can not be stated except as an inference. At Erie, Buffalo, 

 Rochester and Oswego the conditions are somewhat the same as 

 at New York and the humidity shown by tables Nos. 3, 4, 7 and 8 

 is not very different. We need humidity observations for the 

 upper Genesee in order to settle the relation. 



In the growing period vegetation is active and large demands 

 are made upon ground water to supply its requirements. Dur- 

 ing this period, as an average. 2.57 inches of water runs off from 

 the Croton area, although in 1880 only 0.68 inch ran off. As 

 a broad proposition, ground water tends to become lower and 

 lower throughout the growing period. 



In the replenishing period the average runoff from the Croton 

 area is 3.42 inches, from an average rainfall of 12.08 inches. 

 During this period, broadly, ground water is rising and con- 

 ditions tend to restore themselves to that at the beginning of 

 the storage period. The varying conditions on the Genesee and 

 Hudson rivers during these periods may be seen by reference to 

 the tables relating to those streams. 



One great advantage of dividing records into these periods 

 is as follows: Since evaporation and plant absorption are light 

 during the months of the storage period, it follows to a great 

 degree that the amount of water which can be stored is exhibited 

 by the rainfall of the storage months. Realizing this fact, it 



