The complementary relationship in estimation of regional evapotranspiration: The Complementary Relationship Areal Evapotranspiration and Advection-Aridity models

Two implementations of the complementary relationship hypothesis for region al evapotranspiration, the Complementary Relationship Areal Evapotranspirat ion (CRAE) model and the Advection-Aridity (AA) model, are evaluated agains t independent estimates of regional evapotranspiration derived from long-te rm, large-scale water balances (1962-1988) for 120 minimally impacted basin s in the conterminous United States. The CRAE model overestimates annual ev apotranspiration by 2.5% of mean annual precipitation, and the AA model und erestimates annual evapotranspiration by 10.6% of precipitation. Generally, increasing humidity leads to decreasing absolute errors for both models, a nd increasing aridity leads to increasing overestimation by the CRAE model and underestimation by the AA model, with the exception of high, arid basin s, where the AA model overestimates evapotranspiration. Overall, the result s indicate that the advective portion of the AA model must be recalibrated before it may be used successfully on a regional basis and that the CRAE mo del accurately predicts monthly regional evapotranspiration.