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

Increased surface temperatures are expected to cause less precipitation in the form of snow. The impact of decreased snowfall has previously been assumed to not influence streamflow significantly. This work applies a water-balance framework to catchments in the United States and finds a greater percentage of precipitation as snowfall is associated with greater mean streamflow. In a warming climate, precipitation is less likely to occur as snowfall1,2. A shift from a snow- towards a rain-dominated regime is currently assumed not to influence the mean streamflow significantly1,3,4,5. 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 supply3 and ecosystems that can be sensitive to streamflow alterations6, the socio-economic consequences of a reduction in streamflow can be substantial. By applying the Budyko water balance framework7 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.