Recent hydrological response of glaciers in the Canadian Rockies to changing climate and glacier configuration

Abstract

Abstract. Mountain snow and ice greatly influence the hydrological cycle of alpine regions by regulating both the quantity of and seasonal variations in water availability downstream. This study considers the combined impacts of climate and glacier changes due to recession on the hydrology and water balance of two high-elevation basins in the Canadian Rockies. A distributed, physically based, uncalibrated glacier hydrology model developed in the Cold Regions Hydrological Modelling platform (CRHM) was used to simulate the glacier mass balance and basin hydrology of the Peyto and Athabasca glacier basins in Alberta, Canada. Bias-corrected reanalysis data were used to drive the model. The model calculates the water balance of glacierized basins, influenced by the surface energy and mass balance, and considers the redistribution of snow by wind and avalanches. It was set up using hydrological response units based on elevation bands, surface slope, and aspect, as well as changing land cover. Aerial photos, satellite images and digital elevation models (DEMs) were assimilated to represent the changing configurations of glacier area and the exposure of ice and firn. Observations of glacier mass balance, snow, and glacier ice surface elevation changes at glacier and alpine tundra meteorological stations and streamflow discharge at the glacier outlets were used to evaluate the model performance. Basin hydrology was simulated over two periods, 1965–1975 and 2008–2018, using the observed glacier configurations for those time periods. Both basins have undergone continuous glacier loss over the last 3 to 5 decades, leading to a 6 %–31 % reduction in glacierized area, a 78 %–109 % increase in ice exposure, and changes to the elevation and slope of the glacier surfaces. Air temperatures are increasing, mainly due to increasing winter maximum and summer minimum daily temperatures. Annual precipitation has increased by less than 11 %, but rainfall ratios have increased by 29 %–44 %. The results show that changes in both climate and glacier configuration have influenced the melt rates and runoff and a shift of peak flows in the Peyto Glacier basin from August to July. Glacier melt contributions increased/decreased from 27 %–61 % to 43 %–59 % of the annual discharges. Recent discharges were 3 %–19 % higher than in the 1960s and 1970s. The results suggest that increased exposure of glacier ice and lower surface elevation due to glacier thinning were less influential than climate warming in increasing streamflow. Streamflow from these glaciers continues to increase.

Hydrological process controls on streamflow variability in a glacierized headwater basin

“…However, it differed substantially from the CRHM application to the PGRB by Pradhananga and Pomeroy (2022a;2022b). The study used in-situ forcing data instead of reanalysis data (except precipitation) and simulated different time periods (1989-2020in this case and 2013and 1967-1977in Pradhananga & Pomeroy, 2022a. In addition, the current application used a different energy-balance parametrization for the glacier ice melt at an hourly timestep as described in Section 2.2.2 (Snow and ice melt), whilst Pradhananga and Pomeroy (2022a) used a daily formulation without parametrization of sub-debris melt.…”

“…Therefore, the numbers presented here are within the ranges of values obtained in Considering that meteorological extremes are expected to increase in the future, and that glacier retreat enhances flow variability by changing the streamflow regime from ice-dominated to snowmelt and rainfall-runoff dominated, the streamflow in headwater glacierized basins is expected to continue to change in the upcoming decades. Increasingly warm conditions may cause an increase in the frequency of high flow conditions whilst glacier coverage still remains, much as was noted in the shift from the 1960s to recent years by Pradhananga and Pomeroy (2022a). These future changes will be superimposed on the current inter-annual variability that currently dominates the streamflow response in the PGRB.…”

“…The energy balance formulation for the ice and firn melt uses turbulent energy fluxes calculated following the katabatic parametrization of the bulk transfer method as described by Grisogono and Oerlemans (2001) and tested at Peyto Glacier by Munro (2004). This is an advance over the simpler daily ice melt energy balance parameterization employed in CRHM previously by Pradhananga and Pomeroy (2022b;2022a) in that sub-daily fluxes can have important contributions to seasonal melt. If the snowpack is not completely melted by the end of the summer, the snow becomes firn.…”

“…For example, Pradhananga and Pomeroy (2022a) had a spatial discretization with 65 HRUs, and only 37 are used in this study. In addition, the research goals of this study, specifically to investigate processes resulting in streamflow variability in the PGRB, were different from those of Pradhananga and Pomeroy (2022a;2022b), and therefore resulted in a different analysis methodology.…”

“…Since shortwave radiation rather than air temperature is the main driver of glacier melt, and snow redistribution is an important control on snow accumulation, the lack of a physical basis for these models is scientifically unsatisfying in that process diagnoses are not possible and predictive uncertainty is high because they are calibrated to past climate and glacier conditions. Models with a more complete range of representations of glacio-hydrological processes do exist (Frans et al, 2018;Naz et al, 2014;Pradhananga & Pomeroy, 2022b;2022a), but these are still not widely used despite the uptake of models of similar complexity for cold regions hydrological applications (Wheater et al, 2022). To investigate the inter-annual variability in the hydrology of a glacierized headwater basin and to diagnose the hydrological processes governing this variability requires a physically based model, with representations of both on and off-glacier biophysical processes.…”