no 



Water 



rain were evenly distributed through the year. However, the major 

 portion of the rainfall occurs during the spring growing season, and 

 also at a time before the rate of evaporation has become excessive, 

 with the result that the available precipitation is used to best advan- 

 tage. The existing combination of ecological conditions thus permits 

 western Canada to be an important wheat-growing region. 



The foregoing discussion brings into relief the fact that in consider- 

 ing moisture conditions on land the actual amount of the precipita- 

 tion is only part of the story. The other part, and often the more 



5.1 10.2 15.2 20.3 25.4 30.5 35.6 40.6 cm 



°C 

 26.7 



23.9 



21.1 



18.3 



15.6 



12.8 



10.0 



7.2 



4.4 



+ 1.7 



-1.1 



-3.9 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 in. 

 Average monthly rainfall 

 Fig. 4.8. Average rainfall and temperature for each month of the year as indi- 

 cated by the numerals. 



Lower figure: temperate climate— data for Chicago, Illinois. 



Upper figure: tropical climate— data for Barro Colorado Island, 

 Panama Canal Zone. (Reprinted with permis- 

 sion from Hesse, Alice, and Schmidt, Ecological 

 Animal Geography, 1951, John Wiley and Sons, 

 New York. ) 



