SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Analyzing the suitability of remotely sensed ET for calibrating a watershed model of a Mediterranean montane forest 
Authors:Jepsen, S.M., T.C. Harmon and B. Guan 
Journal:Remote Sensing 
Volume (Issue):13(7) 
Article ID:1258 
URL (non-DOI journals): 
Broad Application Category:hydrologic only 
Primary Application Category:evapotranspiration assessment 
Secondary Application Category:hydrologic assessment 
Watershed Description:3,999 km^2 Upper Kings River, located in the southern part of Sierra Nevada Mountain Range in central California, U.S. 
Calibration Summary: 
Validation Summary: 
General Comments: 
Abstract:The ability to spatially characterize runoff generation and forest health depends partly on the accuracy and resolution of evapotranspiration (ET) simulated by numerical models. A possible strategy to increase the accuracy and resolution of numerically modeled ET is the use of remotely sensed ET products as an observational basis for parameter estimation (model calibration) of those numerical models. However, the extent to which that calibration strategy leads to a realistic representation of ET, relative to ground conditions, is not well understood. We examined this by comparing the spatiotemporal accuracy of ET from a remote sensing product, MODIS MOD16A2, to that from a watershed model (SWAT) calibrated to flow measured at an outlet streamgage. We examined this in the upper Kings River watershed (3999 km2 ) of California’s Sierra Nevada, a snow-influenced watershed in a Mediterranean climate. We assessed ET accuracies against observations from three eddy-covariance flux towers at elevations of 1160–2700 m. The accuracy of ET from the stream-calibrated watershed model surpassed that of MODIS in terms of Nash-Sutcliffe efficiency (+0.36 versus −0.43) and error in elevational trend (+7.7% versus +81%). These results indicate that for this particular experiment, an outlet stream gage would provide a more effective observational basis than remotely sensed ET product for watershed-model parameter estimation. Based on analysis of ET-weather relationships, the relatively large errors we found in MODIS ET may be related to weather-based corrections to water limitation not representative of the hydrology of this snow-influenced, Mediterranean-climate area. 
Keywords:evapotranspiration; model; SWAT; calibration; regression; remote sensing; Sierra Nevada; flux tower; water limitation; vapor pressure deficit