The Impact of Precipitation Type Discrimination on Hydrologic Simulation: Rain–Snow Partitioning Derived from HMT-West Radar-Detected Brightband Height versus Surface Temperature Data

Abstract

ourly surface precipitation type (Ptype) grids (a total of 408 h from 1 December 2005 through April 20, 2006) were generated by mapping the elevation of the radar-detected brightband height (BBH) to terrain elevation during the 2005/06 observation period of the western Hydrometeorology Testbed (HMT-West) in the North Fork American River basin. BBH Ptype grids were compared to those derived by the standard National Weather Service (NWS) temperature threshold method. In this method, a fixed threshold temperature separating rain and snow was applied to hourly 4-km gridded temperature data. The BBH Ptype grids agreed well (>90%) with the temperature threshold?based grids below an elevation of 1524 m. The agreement dropped to below 60% above this elevation, and BBH Ptype produced more rainfall than the temperature-based Ptype. Continuous hourly streamflow simulations were generated using spatially lumped and distributed hydrologic models with and without the BBH Ptype data from 1 October 2005 through 30 September 2006. Simple insertion of BBH Ptype data did not always improve streamflow simulations for the 11 events examined relative to corresponding simulations using temperature threshold?derived precipitation type, possibly because of the use of the models calibrated with the temperature-based Ptype. The simple sensitivity test indicated simulations of both peak flows from midwinter storms and spring snowmelt runoff are affected by errors in precipitation type estimates.