WEHY modeling and its sensitivity to precipitation field input: A case study from Cottonwood Creek Watershed.

The Watershed Environmental Hydrology Hydro-Climate Model (WEHY-HCM) allows the simulation of run-off and groundwater flows at a watershed scale using various atmospheric inputs, particularly the precipitation field over a watershed. High-resolution precipitation data is available by dynamical downscaling of global reanalysis data, and it might contribute to better representations of variations in the flow discharge in the target watershed. This study investigated the impacts of precipitation inputs on the simulated flow discharge at the Cottonwood Creek Watershed in the Sacramento River Basin. As the first step, the Cottonwood Creek Watershed WEHY-HCM was developed considering the calibration period from 1997-1999 and dynamically downscaled atmospheric data from Climate Forecast System Reanalysis (CFSR). Then, with two different precipitation inputs, WEHY-HCM discharge simulations were compared: WEHY-CFSR, where the precipitation input was obtained by downscaling of CFSR; and WEHY-PRISM, where the precipitation input comes from the Parameter-elevation Regressions on Independent Slopes Model (PRISM). The simulations indicated that WEHY-PRISM showed better accuracy for higher flows but tended to overestimate the flows. On the other hand, WEHY-CFSR simulation tended to be more equilibrated in lower flows and had a satisfactory performance for the validation period.