Two-Layer Model of Near-Surface Soil Drying for Time-Continuous Hydrologic Simulations

Abstract

A two-layer soil water balance model is developed to provide an efficient and robust description of land surface dynamics in response to atmospheric evaporative events. Soil, vegetation, and atmosphere are coupled dynamically under the assumption that soil moisture profiles approximately preserve similarity during simultaneous atmospheric drying and gravity drainage. The exfiltration flux at the land surface in response to the atmospheric evaporative demand is limited by relating the surface resistance to water vapor transfer in the Penman-Monteith equation to the near-surface soil status. In addition, the control of deeper soils on both exfiltration and drainage is expressed by performing a time compression approximation water balance over the entire drying profile and by scaling the obtained exfiltration and drainage fluxes to the near-surface soil layers. The reliability and robustness of the proposed formulation is evaluated with rates of evaporation calculated from measurements of the Bowen ratio and soil moisture data obtained from time domain reflectometry measurements for a bare soil field in the Zwalmbeek catchment (Belgium).