Investigating the impacts of glacier melt on stream temperature in a cold-region watershed: Coupling a glacier melt model with a hydrological model

Abstract

Stream temperature is a significant indicator for biodiversity and ecosystem health of stream ecosystem. The impacts of glacier melt processes on stream temperature, such as the cooling effect, have not been explicitly considered in process-based models, which limit model capability in simulating stream temperature in glacierized cold regions. We coupled a temperature index-based glacier melt model with the SWAT equilibrium temperature model to overcome this limitation. The coupled model was tested and applied in the upper Athabasca River basin in western Canada to simulate daily streamflow and stream temperature. It showed a good performance for stream temperature simulation with percent bias (PBIAS) less than ±5% and Nash-Sutcliffe efficiency (NSE) and coefficient of determination (R2) values greater than 0.85. The impact of glacier melt runoff on streamflow and stream temperature simulation was investigated by turning the melt model on and off. The results illustrate that the coupled model accurately reproduces the impacts of glacier melt by simulating higher streamflow and lower stream temperature during the melt season. In particular, the progressive reduction in the cooling effect of glacier melt runoff on stream temperature from headwater to downstream was well represented. Finally, the role of glacier melt runoff affecting stream temperature under climate change was assessed by the scenario simulations. This analysis revealed that an increase in glacier melt runoff in the near future would alleviate the average and peak stream temperature increase during the melt season, while a decrease in glacier melt runoff in the distant future would ultimately aggravate the stream temperature increase. Therefore, the impact of glacier melt runoff should be explicitly considered in process-based models to accurately model stream temperature and predict future climate change impact on the thermal regime in the glacierized watersheds. The model coupling framework developed in this study could be a useful tool for simulating stream temperature in glacierized watersheds.