Process-based calibration of WRF-Hydro in a mountainous basin in southwestern U.S.

摘要

The National Water Model (NWM) will provide the next generation of operationalstreamflow forecasts across the United States (U.S.) using the WRF-Hydrohydrologicmodel. In this study, we propose a strategy to calibrate 10 parameters of WRF-Hydrothat control runoff generation during floods and snowmelt seasons, and due to baseflow.We focus on the Oak Creek Basin (820 km~2), an unregulated mountainous sub-watershedof the Salt and Verde River Basins in Arizona, which are the largest sourceof water supply for the Phoenix Metropolitan area. We calibrate the model againstdischarge observations at the outlet in 2008–2011,and validate it at two streamgauging stations in 2012–2016.After bias correcting the precipitation forcings, wesequentially modify the model parameters controlling distinct runoff generation processesin the basin. We find that capturing the deep drainage to the aquifer is crucialto improve the simulation of all processes and that this flux is mainly controlled bythe SLOPE parameter. Performance metrics indicate that snowmelt, baseflow, andfloods due to winter storms are simulated fairly well, while flood peaks caused bysummer thunderstorms are severely underestimated. We suggest the use of spatiallyvariable soil depth to enhance the simulation of these processes. This work supportsthe ongoing calibration effort of the NWM by testing WRF-Hydroin a watershed witha large variety of runoff mechanisms that are representative of several basins in thesouthwestern U.S.