THE CLIMATE OF WESTERN CANADA 13 



The chief factors of climate in order of their relative 

 importance to the agriculture of Western Canada are: 



1. Precipitation: (a) amount per year; (b) geo- 

 graphic distribution; (c) monthly distribution; (d) 

 form (rain, snow, hail, dew) ; (e) variations from the 

 average; and (f) evaporation. 



2. Temperature: (a) the number of days between 

 spring and fall frosts; (b) the average monthly tempera- 

 ture; (c) the range of annual and daily temperature. 



3. Wind: (a) velocity; (b) temperature; (c) humid- 

 ity, and (d) direction. 



4. Atmospheric humidity. 



5. Light during the growing season. 



6. Altitudes and forests. 



6. Importance of Precipitation. Moisture in the soil is 

 essential to crop production. It is needed both as a plant 

 food and as a carrier of plant food. Under semi-arid 

 conditions more than a quarter of a ton of water is taken 

 in through the roots and passed out through the leaves 

 in order to carry enough food into the plant to produce 

 one pound of "dry matter". 



One acre inch of water weighs about 113 tons. As- 

 suming that 700 pounds* is the average requirement for 

 one pound of dry matter in wheat and, for easy calcula- 

 tion, that half the dry matter of wheat is in the stems 

 and leaves, it would take 1,400 pounds of water to pro- 



*Recent investigations by Hopkins at Olds, Alberta, indicate that 

 much less than this amount is required on rich prairie soil in 

 high latitudes. 



