Effects of Dynamic Forcing on Hillslope Water Balance Models

Recently there has been much interest in scaling water flow and species transport at the continuum level to the watershed. A particularly simple and, therefore, appealing approach is based on the water mass balance at the hillslope scale. Such models require parameterization of closure relations (flux–storage relations) based on field data. In several recent studies, this data was instead generated by steady-state numerical simulations of the hillslope. In this work we focus specifically on closure relations for hillslope water balance models as in previous work, but we use transient numerical solutions of continuum-scale models of the subdomain to generate the data. Our goal is to study the effects of non-equilibrium behavior on time-averaged flux–storage relationships for the hillslope. We show that for simulated hillslopes, the flux–storage relations are multivalued for a wide range of time scales, discuss how this situation arises, and provide some alternative parameterizations of the flux–storage relations.