Modeling the Streamflow Response to Heatwaves Across Glacierized Basins in Southwestern Canada

Abstract

AbstractIn addition to having far‐reaching impacts on human health, agriculture, wildfires, ecosystems, and infrastructure, heatwaves control streamflow through the melting of seasonal snow and glacier ice. Despite their importance, there is limited understanding of how heatwaves modify streamflow at regional scales, how these impacts vary by heatwave timing and duration, and how glaciers control the streamflow response. Here, we use a deep learning hydrological model, which has previously been trained, evaluated, and interpreted in southwestern Canada, to simulate the streamflow response to heatwaves at 111 basins in the region. The model, driven by gridded ERA5 reanalysis temperature and precipitation data from 1979 to 2015, is forced by synthetic heatwave conditions that vary in their duration and onset throughout the year. We consider how the streamflow response to heatwaves is sensitive to annual temperatures by adding spatially and temporally uniform warming of 2°C across the study region, under the assumption that the underlying hydrological system behavior remains unchanged. We find that heatwaves, particularly in spring and summer, induce an initial streamflow surplus followed by a streamflow deficit, relative to the non‐heatwave case. In summer, glacier contributions to streamflow partially compensate for streamflow deficits that arise from heatwaves earlier in the melt season. In the scenario with 2°C warmer annual temperatures, heatwaves induce a lesser streamflow response in spring when the seasonal streamflow is most increased due to the advancing freshet. Our findings demonstrate how glaciers buffer the impacts of heatwaves on streamflow, but this buffering effect is expected to diminish as glaciers retreat.