RAINFALL AND EVAPORATION 



Evaporation depends upon the tempera- 

 ture of the evaporating surface, the dry- 

 ness of the air, and the velocity of the 

 wind. The hotter the day, the greater 

 the evaporation; the drier the day, the 

 greater the evaporation; the harder the 

 wind blows, the greater the evaporation 

 — the ceaseless sucking up of moisture. 

 The amount of evaporation from an open 

 tank of water is thus a measure of the 

 evaporation of that locality. The higher 

 the evaporation from the tank, the 

 greater is the moisture demand made 

 upon the soil. Briggs says: "Settlers 

 looking into the possibilities of a new 

 country inquire only regarding the rain- 

 fall. The evaporation is not considered. 

 This is doubtless largely due to the un- 

 fortunate fact that evaporation data are 

 not yet generally available. Such records 

 would be of great value to the settler. In 

 dry-farming the most favorable region, 

 99 



