Sensitivity of Annual Evaporation to Soil and Root Properties in Two Models of Contrasting Complexity

Abstract

Simulations of soil water and evapotranspiration with physically based models at broad scales vary in both complexity of processes modeled and in parameterization of soil and root properties. Sensitivity of annual evaporation Eann to some of these processes and parameters was tested with both a model allowing multiple soil layers (BROOK90) and a single-layered water balance model (WBM). For nine widely scattered locations in North America Eann was controlled primarily by climate and cover type, but within a location–type combination, Eann was controlled primarily by the available water capacity Wac, which is the product of available water fraction and effective root depth. The definition of the upper limit of available water is important; it is precisely defined here as the water volume fraction at 30-cm depth after 48 h of drainage from an initially saturated, homogeneous profile with a fixed gravity potential gradient at 2-m depth. Specification of root depth was as important as specification o... Abstract Simulations of soil water and evapotranspiration with physically based models at broad scales vary in both complexity of processes modeled and in parameterization of soil and root properties. Sensitivity of annual evaporation Eann to some of these processes and parameters was tested with both a model allowing multiple soil layers (BROOK90) and a single-layered water balance model (WBM). For nine widely scattered locations in North America Eann was controlled primarily by climate and cover type, but within a location–type combination, Eann was controlled primarily by the available water capacity Wac, which is the product of available water fraction and effective root depth. The definition of the upper limit of available water is important; it is precisely defined here as the water volume fraction at 30-cm depth after 48 h of drainage from an initially saturated, homogeneous profile with a fixed gravity potential gradient at 2-m depth. Specification of root depth was as important as specification o...