Diagnosis of Hydrological Resiliency and Functional Change in a Canadian Rockies Mountain Basin

Abstract:

A well-instrumented headwater basin in the Canadian Rockies, Marmot Creek Research Basin, has experienced substantial warming at a range of elevations with evidence of hydrological functional change, but there has been no change observed in the streamflow regime over the last 50 years. Despite observations of increased air temperature of up to 4 ^oC in winter, concentration of precipitation into multiple day events in the spring, decreased peak snow accumulation at lower elevations by 50%, and decreased (increased) low (high) elevation groundwater storage; there are no trends in streamflow timing, peak or seasonal volumes since records began in 1962. This suggests a remarkable resilience in runoff generation to changing temperature and precipitation regime in a cold regions basin. To diagnose possible reasons for this resilience the Cold Regions Hydrological Model (CRHM) simulated the basin hydrological processes and response over two periods that had excellent driving meteorology; 1969-1987 and 2006-2013. CRHM calculates all of the relevant hydrological processes including blowing snow redistribution, intercepted snow and rain loss, sublimation, snowmelt, evapotranspiration, infiltration into frozen and unfrozen soils, overland flow, interflow in organic soils, sub-surface runoff in mineral soils, soil water redistribution and groundwater flow. Model results show that compared to the first period, increases in annual, basin-averaged fluxes occurred in the latter period for rainfall (37%), snowfall (20%), snowmelt (30%), evapotranspiration (23%), and sublimation (42%), but no significant trend in runoff developed between the two periods. Snowmelt, sublimation and runoff increases were primarily at high elevations and sometimes reversed at lower elevations, whilst evapotranspiration and rainfall increases were at all elevations. This suggests that there are compensatory, altitude dependent increases in evaporative losses from sublimation and evapotranspiration that promote resiliency in streamflow generation despite profound temperature increases and precipitation regime changes in this basin. Diagnostic hydrological process modelling was essential to understand changes in hydrological functions that were driving the hydrological resiliency to climate change for this basin.