The influence of precipitation type on snowmelt partitioning between evapotranspiration and streamflow

An aspect of hydrologic sensitivity to climate change in snow dominated systems that has been moderately explored relates to the role of snowfall and snowpack accumulation in storing water throughout cold season months and releasing this water to terrestrial systems during warmer months when potential evapotranspiration (PET) is relatively elevated.  Importanlty, previous studies have not been able to document an explicit mechanism linking precipitation type to runoff production; yet several studies have noted that a sensitivity does exist.  Given that a shift from snowfall to rainfall is inevitable as the climate warms, this fundamental question as to how streamflow responds to a change in precipitation type is extremely timely and important for water resource management. Hence, one would expect that climate-related shifts toward earlier snowmelt or a shift from snowfall to rainfall would lead to an increased misalignment between the seasonality of surface water input (i.e. rainfall and snowmelt) and PET, and thus act to decrease annual partitioning to evapotranspiration and increase annual streamflow.  This shift from snowfall to rainfall, and it's associated influence on hydrologic partitioning will be refered to below as the 'energy-water-misalignment perspective'.  A second hypothesis, that is counter to the energy-water-misalignment perspective, has documented an increase in runoff partitioning with increased snowfall fraction which relates to a theorized greater effiency of soil-water drainage from snowmelt versus rainfall due to the high rate and duration of snowmelt; hereafter referred to as the 'snowmelt-rate perspective'.  In pursuit of this line of inquiry, this presentation will cover recent modeling and observation-based experiments that reveal the importance of both of the aforementioned runoff response perspectives.  The combination of these modeling and observation-based studies confirm that the energy-water misalignment perspective and the snowmelt-rate perspective both influence hydrologic partitioning sensitivity to precipitation type.  The resultant streamflow sensitivity to precipitation type and climate warming is therefore complex with the sign of the partitioning sensitivity being governed by the relative importance of the two paradoxical runoff response perspectives presented herein.