Observed trends and future projections of precipitation and air temperature in the Lake Winnipeg watershed

While the cause of eutrophication in Lake Winnipeg is known to be excess nutrient loading from watershed sources, few comprehensive studies have attempted to quantify the effects of changes in temperature and precipitation on the hydrological and nutrient transport regimes in the region. In this paper, results of spatial and temporal analyses of observed and regional climate model (RCM) projections of precipitation and air-temperature regimes within the Lake Winnipeg watershed (LWW) are presented. The Mann–Kendall trend analysis of observed data over a recent time period of 1961 to 2003 shows that, while there has been a consistent increasing trend in the mean annual air temperature in the region, there is no significant trend in annual precipitation. Seasonally, precipitation exhibited a significantly decreasing trend in the Saskatchewan and Assiniboine river basins during the winter and an increasing trend in part of the Red and Assiniboine river basins during summer season. Air temperatures showed significant increases in winter, spring and summer throughout the LWW. Future climate projections from three RCMs driven by the SRES's A2 emission scenario indicate that by the 2050s (2041–2070), total annual precipitation (air temperature) increases by 5.5–7.7% (2.1–2.8°C) compared to the 1980s (1971–2000). These observed and projected changes in the climate regimes of the LWW will have important implications for the hydrology and nutrient transport regimes of this region, which is the subject of additional investigation in a companion paper of this special issue (Shrestha et al., 2012).