Hydrologic Modeling of an eastern Pennsylvania watershed with NEXRAD and rain gauge data

This paper applies the Soil Water Assessment Tool (SWAT) to model the hydrology in the Pocono Creek watershed located in Monroe County, Pa. The calibrated model will be used in a subsequent study to examine the impact of population growth and rapid urbanization in the watershed on the base flow and peak runoff. Of particular interest in this paper is the exploration of potential use of Next Generation Weather Radar (NEXRAD) technology as an alternative source of precipitation data to the conventional surface rain gauges. NEXRAD estimated areal average precipitations are shown to compare well with the gauge measured ones at two climate stations in the study area. Investigation of the spatially distributed NEXRAD precipitation estimates revealed that average annual precipitation can vary spatially as much as 12% in the Pocono Creek watershed. The SWAT model is calibrated and validated for monthly stream flow, base flow, and surface runoff. Hydrographs generated from both gauge and NEXRAD driven model simulations compared well with observed flow hydrographs. Although little effort is spent on daily calibration, model simulations and observed flows were in good agreement at the daily scale as well. Almost similar model efficiency statistics, i.e., mass balance error (MBE), coefficient of determination (R-2), and Nash-Sutcliffe efficiency (E-NS), were obtained during the calibration period in the gauge and NEXRAD driven simulations. In the validation period, NEXRAD simulations generated higher model efficiencies at the monthly scale. On the other hand, simulations with gauge precipitations resulted in slightly better model efficiencies at the daily time scale. The spatial representation of precipitation did not contribute much to model performance when stream flow at the watershed outlet was the required output. However, the use of NEXRAD technology appears to offer a promising source of precipitation data in addition to currently existing surface gauge measurements. Discussions on new directions in radar-rainfall technology are provided.