Authors: Guo-Yue Niu – University of Arizona
Title: Representing preferential flow in macroscale hydrological models
Abstract: To improve the predictability of soil moisture dynamics and runoff production, we develop a mixed-form Richards’ equation solver in Noah-MP. With spatially variable soil depth, this new solver better represents soil moisture and groundwater dynamics, infiltration of surface ponding, and groundwater recharge. Switching its atmospheric boundary condition (BC) between head (Dirichlet) BC and flux BC (or Neumann), the solver explicitly computes infiltration, surface ponding height, and infiltration-excess runoff. The solver computes the pressure continuously across unsaturated and saturated zones and hence the groundwater recharge driven by hydraulic gradient. Based on this, we further developed a dual-permeability model to represent preferential flow. The new solver within Noah-MP also provides optional soil hydraulics (van Genuchten and Clapp-Hornberger models). This iterative solver within Noah-MP does not substantially enhance the computational cost compared to the original mass-based Richards equation solver.