资源环境科技发展态势分析平台

Snowpack accumulation/ablation affects the runoff response to precipitation by modulating the water flux reaching the surface. Previous studies mostly focused on "rain-on-snow" events. Here we propose a framework to extend the scope and classify precipitation events accompanied by snow accumulation/ablation (precipitation-and-snow, or PAS, events) into five regimes. This framework is applied to a regional climate simulation over the western United States for 1981-2015 to reveal regions where daily changes in snowpack alter the surface hydrologic responses to precipitation. Over the western United States, PAS events account for 50-90% of all the precipitation events. Compared to the broad spatial distribution of snow accumulation-type PAS events, snowmelting-type PAS events are limited to coastal high-elevation areas. Atmospheric rivers, a key driver of heavy precipitation in the region, account for only 2% of the PAS events, but they trigger significant snowmelt, accounting for 20% and 11% of light and heavy snowmelting events, respectively.