Uncertainties in Hydrologic and Climate Change Impact Analyses in Headwater Basins of British Columbia

Three headwater basins located across British Columbia (BC) were analyzed using a hydrologic model driven by five global climate models (GCMs) and three scenarios from the Special Report on Emissions Scenarios (SRES) to project future changes in seasonal water budgets and assess the uncertainty in the projections arising from GCMs, emissions scenarios, and hydrologic model parameterizations under two future time periods. Future projected changes in temperature are for annual increases of approximately +2 degrees C by the 2050s and +3 degrees C by the 2080s. The 2050s and 2080s precipitation projections are for increased winter precipitation in all basins and decreases in summertime precipitation for two of the three basins-with increases projected in the northeastern BC subwatershed. The study found that the hydrologic parameter uncertainty ranged up to 55%, (average 31%) for winter runoff anomalies, which was less than the uncertainty associated with GCMs and emissions scenarios that ranged up to 135% and 78% (average 84% and 58%, respectively). The uncertainty results were variable across the three hydroclimate regimes. Coastal headwater systems in British Columbia experience more uncertainty associated with changes during winter and the summer, whereas interior systems experience the greatest uncertainties during the winter and spring. Changes projected for the 2050s at the coastal site fell outside of the range of natural variability, a robust shift that may result in a very different regime for this basin within the short planning horizon of 50 years. A small, semiarid watershed located on the Chilcotin Plateau exhibited changes to the hydrologic regime that were projected to be small in absolute terms and fell within the range of natural variability.