650 



FUNDAMENTALS OF FRUIT PRODUCTION 



Beaupr^ in Quebec, 200 miles north of the general northern limit for the 

 same varieties. 



Probably it would be difficult to separate entirely the different 

 influences of bodies of water upon climate, assigning to air drainage or to 

 increased atmospheric humidity exact figures representing their pro- 

 tective effects. The fact, however, that these other protective influences 

 are at work does not lessen in importance the air drainage that is asso- 

 ciated with water surfaces. 



Minor Temperature Effects. — Even small bodies of water have meas- 

 urable, though slight, influences on temperature. Observations of mini- 

 mum temperatures near a stream 40 feet wide in England, summarized 

 in Table 13, show that the extent of the influence varies. 



Table 13.- 



-AvERAGE Minimum Temperatures (Centigrade) At and Near River 

 Bank^o 



Importance during the Winter.^ — Attention has been called particularly 

 to the effects of air drainage on temperature during the soring and fall 

 months and its bearing on the occurrence of frosts. It should not be in- 

 ferred, however, that air drainage does not take place during other sea- 

 sons where elevation and topography make it possible. Figures 69 and 

 70 show differences in minimum temperatures during some of the winter 

 months between stations at unequal elevations in a mountain valley in 

 Utah. These range between 2° and 8°F. on the coldest nights for stations 

 having 64 feet disparity in elevation and are about 10° for stations having 

 350 feet variance in altitude. Such differences in minimum temper- 

 atures during midwinter may often influence the amount of certain kinds 

 of winter injury or winter killing experienced. Air drainage, therefore, is 

 sometimes of as great importance in preventing winter injury as it is in 



