Vadose Zone Evapotranspiration Distribution Using One-Dimensional Analysis and Conceptualization for Integrated Modeling

Movement of water into and through the vadose zone is of great importance to the assessment of agricultural management, and natural resource protection. The process of water movement changes dramatically over time and space. Vadose zone processes are recognized for controlling both short-term dynamics in watershed hydrology and long-term water balances of hydrologic basins: In this paper, a one-dimensional model, HYDRUS-1D, is used to analyze evapotranspiration (ET) contribution from different regions of the vadose zone. Model concept was based on solving Richard's equation for a soil column subject to ET stress and analyzing the changes in the soil water content along the column. The results of this analysis can be used in developing and validating integrated surface and groundwater models. Fundamental to integrated modeling is the concept to allocate ET demand within the saturated and unsaturated zones. A comparison of the approach of the Integrated Hydrologic Model (MM) with the solution derived by the one-dimensional analysis is presented. The simulation results matched those derived from the IHM three-layer concept. The results validated three of the four thresholds that control ET distribution demand along a soil column, as defined in IHM. The fourth threshold matched but to lesser degree due to the difference of capillary fringe definitions between the two models.