Seasonal and spatial patterns of rainfall trends on the Canadian prairies

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 Ca nadian prairies. Annual rainfall was further split into three 4-month seaso nal groups of amounts and events, and similar analysis was performed on the se variables. There has been a significant increase in the amounts and numb er of rainfall events during the most recent 40-yr period (1956-95). Increa se 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-Ap ril) experienced proportionately the largest increase, with amount and numb er increasing by 46% and 64%, respectively, during the 40-yr period. This r esult may be related to the conversion of snow to rain as a result of warmi ng during this period. The increases in rainfall amount and number of event s 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 n umber of events were not uniform across the prairies, with the least increa se in number and amounts of rainfall in southern Manitoba, Canada, and the largest increase in Alberta and Saskatchewan, Canada. Little or no change i n amounts was obtained in the northern portion of the prairie provinces. Th e results confirmed that the prairies are not getting drier; however, there are seasonal and spatial differences in rainfall trends on the prairie.