Hydrologic response to scenarios of climate change in sub watersheds of the Okanagan basin, British Columbia

Scenarios of climate change were generated for the Okanagan Basin, a snow-driven semi-arid basin located in the southern interior region of British Columbia. Three global climate models (GCMs) were used to generate high (A2) and low (B2) emission scenarios; the canadian global coupled model (CGCM2), the Australian developed CSIROMk2, and the HadCM3 model developed at the Hadley Centre in the United Kingdom. The three time periods simulated were 2010–2039 (2020s), 2040–2069 (2050s) and 2070–2099 (2080s). An increase in winter temperature of 1.5–4.0 °C and a precipitation increase of the order of 5-20% is predicted by the 2050s. Modelled summer precipitation is more variable with predicted change ranging from zero to a 35% decrease depending on the GCM and emission scenario. Summer temperatures were simulated to increase by approximately 2–4 °C. The UBC Watershed Model was used to model the hydrologic response of gauged sub watersheds in the basin under the altered climates. All scenarios consistently predicted an early onset of the spring snowmelt, a tendency towards a more rainfall dominated hydrograph and considerable reductions in the annual and spring flow volumes in the 2050s and 2080s. Of the three climate models, the CGCM2 model provided the most conservative predictions of the impacts of climate change in Okanagan Basin. Simulations based on the CSIROMk2 climate model suggested greatly reduced snowpack and flow volumes despite a sizeable increase in the winter precipitation. The scenarios raise questions over the availability of future water resources in the Okanagan Basin, particularly as extended periods of low flows into upland reservoirs are likely to coincide with increased demand from agricultural and domestic water users.