Using Radar Data to Partition Precipitation into Rain and Snow in a Hydrologic Model

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American Society of Civil Engineers


Simulation of whether precipitation arrives at the land surface in a liquid or frozen state can have a pronounced effect on the peak flows produced by a hydrologic model. While many hydrologic models rely on surface air temperature to discriminate precipitation type, both past studies and the current effort indicate that there can be substantial shortcomings in that approach. As an alternative, the 0°C level detected by a vertically pointing radar is used in two modes, one by ingesting the 0°C level directly into a hydrologic model to determine precipitation type at the land surface, and a second by deriving average surface air temperature thresholds using the radar data. Where snowfall and snow melt are important, using radar-detected 0°C levels can provide a measurable improvement in simulated flow response. The derived surface air temperature thresholds recovered most of the benefit for streamflow prediction obtained by using the 0°C level directly in the hydrologic model for the period concurrent with the radar observations, but these temperature thresholds were not generally transferable to other regions or periods.