A precipitation shift from snow towards rain leads to a decrease in streamflow

In a warming climate, precipitation is less likely to occur as snowfall(1,2). A shift from a snow-towards a rain-dominated regime is currently assumed not to influence the mean stream-flow significantly(1,3-5). Contradicting the current paradigm, we argue that mean streamflow is likely to reduce for catchments that experience significant reductions in the fraction of precipitation falling as snow. With more than one-sixth of the Earth's population depending on meltwater for their water supply(3) and ecosystems that can be sensitive to streamflow alterations(6), the socio-economic consequences of a reduction in streamflow can be substantial. By applying the Budyko water balance framework(7) to catchments located throughout the contiguous United States we demonstrate that a higher fraction of precipitation falling as snow is associated with higher mean streamflow, compared to catchments with marginal or no snowfall. Furthermore, we show that the fraction of each year's precipitation falling as snowfall has a significant influence on the annual streamflow within individual catchments. This study is limited to introducing these observations; process-based understanding at the catchment scale is not yet provided. Given the importance of streamflow for society, further studies are required to respond to the consequences of a temperature-induced precipitation shift from snow to rain.