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The region is characterized by a semi-arid climate that carries abundant sunshine and warm weather throughout the summer and early fall, and a landscape that is largely composed of flat areas with low permeability soils. While these features together result in an area that has exceptional farming conditions, they also cause excessive evaporation. The risk of evaporation has always been prevalent in the Prairies with several significant droughts over the past century and their frequency and severity is increasing more recently. Current estimates indicate that evaporation from the surface of Lake Diefenbaker accounts for more water loss than all other withdrawal sources combined, such that a single millimetre of vaporized water is equivalent to as much as 430,000 cubic metres.
The amount and rate of evaporation are physically governed by: (1) the surface area of an exposed water body or a wetted soil, and (2) atmospheric variables (wind speed, temperature, humidity, and sunshine). A bigger surface area means a larger amount of water is available to evaporate; while warm, sunny, windy, and dry conditions lead to a faster rate of evaporation. Estimating evaporative losses from exposed surfaces is complex, especially in large-scale settings. This has prompted the authors at the University of Regina to develop specialized equipment for simulating atmospheric conditions.
The plan to move substantial water flow via open canals and to irrigate large areas of land will increase the exposed surface area and, as such, increase the amount of water available to evaporate. Similarly, the predicted rise in air temperature and extreme weather events (drought severity and intensity) reported by the Intergovernmental Panel on Climate Change are expected to continue, thereby increasing the rate of evaporative loses. Likewise, the planned change in irrigation practices can lead to soil salinization because the water is known to contain dissolved salts. Salinization occurs as dissolved salts precipitate in the soil when irrigated water leaves the surface by evaporation instead of infiltration. When soil salinity reaches a certain point, the salts become toxic to plants and hinder nutrient interactions and water uptake by roots, all of which results in poor plant health and a loss of yield. Such situations have occurred in the vicinity of large reservoirs and similar climates elsewhere around the globe.