Snowmelt runoff sensitivity analysis to drought on the Canadian prairies

The Canadian prairies are subject to severe extended droughts that are characterized by warmer temperatures, lower precipitation, lower soil moisture and sparser vegetation than normal conditions. The physically based cold regions hydrological modelling platform (CRHM) provides a possible means to analyse the sensitivity of prairie snowmelt processes to drought. The model was tested against detailed observations from Creighton Tributary of the Bad Lake Research Basin, Saskatchewan for the 1974-1975 and 1981-1982 hydrological years and found to perform satisfactorily in reproducing snow accumulation and streamflow without parameter calibration. By lowering winter precipitation and raising winter air temperature from actual meteorological observations and by lowering fall soil moisture and vegetation height parameters, the resulting drought condition sensitivity of snow accumulation, snow cover duration, sublimation of blowing snow, evaporation, infiltration into frozen soils, soil moisture storage change, snowmelt runoff and streamflow discharge was estimated. Snow accumulation and snow cover duration were relatively insensitive to meteorological changes associated with drought because the suppression of blowing snow sublimation moderated reduced snowfall. Infiltration, soil moisture storage change and evaporation were also relatively insensitive to drought conditions. However, lower precipitation, higher air temperature and lower initial soil moisture caused a marked reduction in snowmelt runoff. Similarly, large reductions in streamflow discharge were caused by diminished winter precipitation, increased winter air temperature and decreased fall soil moisture content. A scenario showed that a combination of these factors could cause complete cessation of spring streamflow even under moderate drought of 15% reduction in winter precipitation and 2·5 °C increase in winter mean air temperature. Results show that spring runoff and streamflow discharge are inherently unstable in the Canadian prairie environment, and so, magnify the impacts of drought, and through multi-season storage and vegetation change can cause the impacts of hydrological drought to persist for several seasons after meteorological drought has ended.