Development and assessment of an efficient vadose zone module solving the 1D Richardsʹ equation and including root extraction by plants

From the non iterative numerical method proposed by [Ross, P.J., 2003. Modeling soil water and solute transport—fast, simplified numerical solutions. Agronomy Journal 95, 1352–1361] for solving the 1D Richardsʹ equation, an unsaturated zone module for large scale hydrological model is developed by the inclusion of a root extraction module and a formulation of interception. Two root water uptake modules, first proposed by [Lai, C.-T. and Katul, G., 2000. The dynamic role of rott-water uptake in coupling potential to actual transpiration. Adv. Water Res. 23: 427–439; Li, K.Y., De Jong, R. and Boisvert, J.B., 2001. An exponential root-water-uptake model with water stress compensation. J. Hydrol. 252: 189–204], were included as the sink term in the Richardsʹ equation. They express root extraction as a linear function of potential transpiration and take into account water stress and compensation mechanism allowing water to be extracted in wetter layers.