The complementary relationship in estimation of regional evapotranspiration: An enhanced advection‐aridity model

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Abstract
Long‐term monthly evapotranspiration estimates from Brutsaert and Strieker's Advection‐Aridity model were compared with independent estimates of evapotranspiration derived from long‐term water balances for 139 undisturbed basins across the conterminous United States. On an average annual basis for the period 1962–1988 the original model, which uses a Penman wind function, underestimated evapotranspiration by 7.9% of precipitation compared with the water balance estimates. Model accuracy increased with basin humidity. An improved formulation of the model is presented in which the wind function and the Priestley‐Taylor coefficient are modified. The wind function was reparameterized on a seasonal, regional basis to replicate independent proxy potential evapotranspiration surfaces. This led to significant differences from the original Penman wind function. The reparameterized wind function, together with a recalibrated Priestley‐Taylor coefficient in the wet environment evapotranspiration formulation, reduced the underestimation of annual average evapotranspiration to only 1.15% of precipitation on an independent set of validation basins. The results offered here lend further support for Bouchet's hypothesis as it applies to large‐scale, long‐term evapotranspiration.