The major factor in determining the production of western farms is the amount of water available for plant growth. Climatic fluctuations apart, this quantity has apparently diminished as a result of settlement. This diminution of the water supply seems to be the main cause of the disquieting decline in the productivity of the Canadian prairies; though the decline may have been due in part to the loss of those advantages which are enjoyed for a brief time by newly cultivated land, viz., relative freedom from plant disease, insect pests, and weeds.

The supply of soil water depends on three factors—precipitation, evaporation, and the nature of the soil, each of which is subject to considerable local and regional variation, and the variations in which are roughly indicated by the natural vegetative cover. The northern forest belt indicates a plentiful water supply; the long grass region of the foot-hills and the park belt areas have normally an adequate supply, which, in spite of sporadic drought, can be depended upon to yield a satisfactory volume of agricultural produce. The short grass area, extending along the forty-ninth parallel from the Manitoba boundary to the foot-hills, and narrowing northward to the Saskatchewan River in the vicinity of Battleford, has an inadequate supply of water, yet it is one of the most highly developed areas in Western Canada. Here the decline in productivity has been catastrophic. In spite of occasional wet years, there appears to be a chronic and increasing shortage of soil water.