From the beginning of Canadian settlement, the major challenge facing agriculture has been to adapt to the rigours of an extreme, and vanable, climatic environment. Nowhere is this struggle better epitomised than in the three Prairie Provinces of Albertac Saskatchewan and Manitoba. With annual pre-cipitation amounts everywhere below 500mm, and locally as little as 250mm, the climate of the Prames can justifiably be described as semi-arid (Summerville 1981), and their vulnerability to even small departures from the climatic norm may be appreciated. Over large areas as little as 50m of rainfall can make the difference between abundance and economic crisis, particularly during late spring and early summeer when the developing crops are in greatest need of moisture. This sensitivity was tragically demonstrated during the 1984 growing season.