Climate-induced alteration of hydrologic indicators in the Athabasca River Basin, Alberta, Canada

The hydrologic response of the Athabasca River Basin (ARB) in Alberta to projected changes in the future climate is investigated using the Variable Infiltration Capacity (VIC) process-based and distributed hydrologic model. The model forcings are derived from a selected set of GCMs from the latest Coupled Model Intercomparison Project (CMIP5) statistically downscaled to a higher resolution (10 km) over Canada. Twelve hydrologic indicators that represent the magnitude and timing of the hydrologic regimes are evaluated for three 30-year time periods centered at the 1990s, 2050s and 2080s to identify significant alterations of hydrologic regimes between the reference and the two future periods using a t-test at 5% significance level. Hydrologic alteration factors (HAF) are also evaluated for each hydrologic indicator using the range of variability approach (RVA) to investigate projected changes in the distribution of these indicators. The results show increases in spring and winter flows for the two future periods at all hydrometric stations within the basin, resulting in an extended period of spring freshet. A higher rate of increase is projected for the stations located at the upper reach of the river because of the combined effects of increased precipitation and earlier snowmelt resulting from a warming climate. By contrast, summer flows are projected to decrease by up to 21% on average in the 2080s over most of the mainstem stations because of earlier snowmelt, increased evapotranspiration and no significant increase in summer precipitation. A water-management rule that optimizes impacts of water withdrawal from the lower reach of the Athabasca River under the current condition is also applied to the future scenarios to assess its relative performance under the projected climate conditions. The results indicate possible improvement in the water resources system performance in terms of increased reliability and resilience and reduced vulnerability during the two future periods as compared with those in the reference period mainly because of the projected increases in spring and winter flows, which has the potential to offset an expected future water deficit.