Seasonal and Spatial Patterns of Rainfall Trends on the Canadian Prairies

Abstract

Regression analysis was used to establish linear trends of rainfall amounts and number of events at 140 stations with 40 years of record across the Canadian prairies. Annual rainfall was further split into three 4-month seasonal groups of amounts and events, and similar analysis was performed on these variables. There has been a significant increase in the amounts and number of rainfall events during the most recent 40-yr period (1956?95). Increase in annual rainfall was 51 mm, or about 16% of the 40-yr mean, while the number of rainfall events increased by 17, or about 29%. Spring (January?April) experienced proportionately the largest increase, with amount and number increasing by 46% and 64%, respectively, during the 40-yr period. This result may be related to the conversion of snow to rain as a result of warming during this period. The increases in rainfall amount and number of events during summer (May?August) were similar to the annual patterns. There was no significant increase in amount and number of rainfall events during the autumn season (September?December). The increases in rainfall amount and number of events were not uniform across the prairies, with the least increase in number and amounts of rainfall in southern Manitoba, Canada, and the largest increase in Alberta and Saskatchewan, Canada. Little or no change in amounts was obtained in the northern portion of the prairie provinces. The results confirmed that the prairies are not getting drier; however, there are seasonal and spatial differences in rainfall trends on the prairie.