Root-Water-Uptake Based upon a New Water Stress Reduction and an Asymptotic Root Distribution Function

A water stress–compensating root-water-uptake module was developed based upon a newly proposed water stress reduction function and an asymptotic root distribution function. The water stress reduction function takes into account both soil water pressure head and soil resistance to water flow. It requires only physically based parameters that eliminate the need for empirical calibration. The root-water-uptake module, incorporated into a complete Soil–Vegetation–Atmosphere Transfer (SVAT) simulation model, was tested for a variety of soil, crop, and climatic conditions across Canada. Both the proposed water stress reduction and the asymptotic root distribution function performed similarly to existing ones, with the maximum difference in normalized root-mean-square error (NRMSE) between the new and existing water stress reduction function being 0.6%, and between the asymptotic and an exponential root distribution function being 1.2%. The entire root-water-uptake module worked as well as, or better than, published ones. Because the new module uses fewer empirical parameters, it becomes particularly useful in large-scale modeling applications of land surface, hydrology, and terrestrial ecosystems where such parameters are usually not readily available.