Melt trends portend widespread declines in snow water resources

Abstract In many mountainous regions, winter precipitation accumulates as snow that melts in spring and summer providing water to one billion people globally. As the climate warms and snowmelt occurs earlier, this natural water storage is compromised. While snowpack trend analyses commonly focus on snow water equivalent (SWE), we propose that trends in accumulation season snowmelt serve as a critical indicator of hydrologic change. We compare long-term changes in snowmelt and SWE from snow monitoring stations in western North America. Nearly four-times more stations have increasing winter snowmelt trends than SWE declines; significant (p<0.05) at 42% vs. 12% of stations, respectively. Snowmelt trends are highly sensitive to temperature and an underlying warming signal, while SWE trends are more sensitive to precipitation variability. Thus, continental-scale snow-water resources are in steeper decline than is inferred from widely reported SWE trends alone. More winter snowmelt will complicate future water resources planning and management efforts.