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

In 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 degrees 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 degrees 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. Heatwaves are periods of extremely warm temperatures that can have profound consequences on not only human health, agriculture, wildfires, ecosystems, and infrastructure, but also on river flows. We use a model to simulate river flows throughout southwestern Canada under heatwave conditions. We find that 1 week of extreme heat can influence river flows for several months by changing the timing and amount of snow and glacier melt. Excess melt during heatwaves can lead to river flows that initially are higher than they otherwise would be; however, river flows later in the season are then lower than they otherwise would be. Glacierized rivers are unique in that glaciers melt during summer, which can compensate for heatwaves that melt snow earlier in spring. If average temperatures were warmer by 2 degrees C, heatwaves could melt more snow and ice during winter and early spring, but less in late spring and summer. We use a deep learning hydrological model to quantify streamflow responses to simulated heatwaves that vary in duration and date of onsetHeatwaves drive initial streamflow surpluses and delayed streamflow deficits that are linked to heatwave timing and glacier coverageWith warmer annual temperatures, spring heatwaves drive lesser streamflow responses when streamflow is most increased by the earlier freshet

Automated summary

Heatwaves not only have wide-ranging impacts on various aspects, including human health and agriculture, but also control streamflow through the melting of snow and glacier ice. This study uses a deep learning hydrological model to simulate the streamflow response to heatwaves in southwestern Canada and finds that glaciers can buffer the impacts of heatwaves on streamflow.