Investigation hydrologic responses to rain-on-snow events in the western United States

Snow water storage provides critical water resources and ecologic flows in arid western United State. Recent meteorological records and climate projections has suggested more rain-on-snow (ROS) events in the western US. Hydrologic responses including spring floods and summer droughts to ROS events are fundamental to hazard prediction and water resource management, while have not yet been thoroughly investigated. In this study, we compile meteorological and hydrologic observations in 907 small watersheds western US and analyze the relationships between ROS events and hydrologic signatures for both high flow and baseflow. Here, we define a ROS event as heavy rainfall of at least 10 mm d^-1 falling on snowpack with at least 3 mm snow water equivalent, where the sum of rainfall and snowmelt contains at least 20% snowmelt. We investigate: 1) the correlation between ROS events and frequency or magnitude of high flow to evaluate the contribution of ROS processes peak flows generation mechanism; 2) the seasonal impacts of ROS on summer baseflow to provide insights for water resources management; 3) the spatial distribution and temporal trends of ROS events and their implications to hydrologic changes. The results from this study will provide better understanding of the relative importance of ROS for both high flow and baseflow in the western US and better support to facilitate hazard prediction in different regions.