Abstract
Accurate gridded estimates of evapotranspiration (ET) are essential to the analysis of terrestrial water budgets. In this study, ET estimates from three gridded energy-balance based products (ET(EB)) with independent model formations and data forcings are evaluated for their ability to capture long term climatology and inter-annual variability in ET derived from a terrestrial water budget (ET(WB)) for 671 gaged basins across the CONUS. All three ET(EB) products have low spatial bias and accurately capture inter-annual variability of ET(WB) in the central US, where ET(EB) and ancillary estimates of change in total surface water storage (ΔTWS) from the GRACE satellite project appear to close terrestrial water budgets. In humid regions, ET(EB) products exhibit higher long-term bias, and the covariability of ET(EB) and ET(WB) decreases significantly. Several factors related to either failure of ET(WB), such as errors in ΔTWS and precipitation, or failure of ET(EB), such as treatment of snowfall and horizontal heat advection, explain some of these discrepancies. These results mirror and build on conclusions from other studies: on inter-annual timescales, ΔTWS and error in precipitation estimates are non-negligible uncertainties in ET estimates based on a terrestrial water budget, and this confounds their comparison to energy balance ET models. However, there is also evidence that in at least some regions, climate and landscape features may also influence the accuracy and long-term bias of ET estimates from energy balance models, and these potential errors should be considered when using these gridded products in hydrologic applications.