Heatwaves drive rapid snowmelt and disrupt streamflow in the western United States

Heatwaves, characterized by prolonged periods of abnormally high temperatures, could affect snowpack and water resources. Utilizing observations from 2001 to 2024, this study quantifies and evidences the pronounced impacts of heatwaves on daily snowmelt rates and subsequent river discharge over the western United States. We found that at least 250 of 823 Snow Telemetry stations (approximately 30%) have experienced heatwaves at least once over the past 24 years, and that 98% of them exhibit faster-than-normal snowmelt rates. Specifically, heatwaves increased the probability of faster-than-normal melting from around 50% to over 90%. This study also found that the influence of heatwaves on snowmelt rate persists for 3–5 days after heatwave events, with the longest persistence effects in spring. While it is expected that streamflow spikes following heatwave events due to accelerated snowmelt, such fluctuations were detected in only 55% of the impacted watersheds in the streamflow observations.