Soil Evaporation Stress Determines Soil Moisture-Evapotranspiration Coupling Strength in Land Surface Modeling

Model-based estimates of soil moisture (SM)-evapotranspiration (ET) coupling strength (rho) vary widely and are prone to bias. Here we apply numerical modeling and remote sensing to identify the process-level source of modeled rho bias with the goal of improving the fidelity of current Earth system models. Results illustrate that modeled rho is most strongly determined by soil evaporation (E) stress, and (generally positive) rho modeling bias is attributable to the oversimplification of soil texture impacts on E stress. Based on new remotely sensed estimates of rho, we demonstrate that removing rho bias via a single optimized E stress parameter leads to improved ET accuracy and resolves a well-known modeling bias in the partitioning of ET into E and T. As such, we highlight the importance of the stress function relating E and SM and its central role in regulating land-atmosphere coupling processes impacting local climate.