A calibration-free, robust estimation of monthly land surface evapotranspiration rates for continental-scale hydrology

Abstract

Continuous simulation of monthly evapotranspiration rates for 1979–2015 was performed by the latest, calibration-free version of the complementary relationship of evaporation over the conterminous United States. The results were compared to similar estimates of the WREVAP program and the North American Regional Reanalysis (NARR) project. Validation of the three methods was performed by the Parameter-Elevation Regressions on Independent Slopes Model precipitation and Hydrologic Unit Code level-6 runoff data. The present method outperforms the WREVAP and NARR estimates with a root-mean-square error (RMSE) of 89 mm yr1, an R2 value of 0.87, an absolute bias (s) of 5 mm yr1, and slope (m) and intercept (c) values of 0.97 and 22 mm yr1, respectively, for the best-fit line, in comparison to similar values (RMSE ¼ 161 mm yr1, R2 ¼ 0.8, s ¼ 124 yr–1 mm yr1, m ¼ 0.88, c ¼ 191 mm yr1; and RMSE ¼ 195 mm yr1, R2 ¼ 0.81, s ¼ 146 mm yr1, m ¼ 1.05, c ¼ 120 mm yr1) of the latter two methods. The value of the Priestley–Taylor (PT) coefficient was determined by inversion of the PT-equation via a model-independent identification of wet cells and their estimated surface temperatures.