Impacts of climate change on nutrient losses from the Pike River watershed of southern Quebec

The impacts of climate change on water quality in the Pike River watershed, an important contributor of nutrient loads into the northern arm of Lake Champlain, were simulated for the time horizon 2041-2070. Four water quality scenarios were simulated using a calibrated version of the Soil and Water Assessment Tool (SWAT) customized to Quebec agroclimatic conditions. Three of the scenarios were generated using climate data simulated with the Fourth-generation Canadian Regional Climate Model (CRCM4). The fourth scenario was generated using the climate simulated with the Arpege Regional Climate Model. Potential mean climate-induced changes in sediment, phosphorus, and nitrogen yield projected by these scenarios were then analyzed for the 2050 horizon. In addition, the impacts of the different sources of climate projection uncertainty were assessed by comparing climate model initial conditions, and climate model physical structure effects on the hydrochemical projections. Only one climate scenario projected a significant increase in mean annual total phosphorus [10 metrics tons (t) yr(-1) or 14%] and total nitrogen (260 t yr(-1) or 17%) loads. However, when shorter time spans (seasonal and monthly scales) were considered, several significant changes were detected, especially in winter. Sediment and nutrient loadings, in winter, were predicted to become three to four times higher than current levels. These increases were attributed to a greater vulnerability of soils to erosion in winter due to the decrease in the snowpack, early onset of spring snowmelt, a greater number of rainfall events, and snowmelt episodes caused by higher winter and spring temperatures.