Land surface characteristics such as topography, soil and vegetation are recognized to exert spatial controls on hydrologic responses. Nevertheless, the temporal evolution of these controls is poorly understood. In addition, the effects of model resolution on reliable spatial simulations are untested at hillslope scales. In this study, we utilize a distributed hydrologic model, the TIN-based Real-time Integrated Basin Simulator (tRIBS), to explore the temporal evolution of spatial controls on soil moisture and runoff production in a Ponderosa pine hillslope. High resolution LIDAR (0.328 m) are used to parameterize the topography and vegetation cover in the highly-instrumented hillslope site. Due to this data availability, we investigate the impacts of model resolution to identify an optimum modeling support. The simulations over three-month summer periods in 1996 to 1998 are in good agreement with distributed soil moisture data from 14 profile locations and 3 hillslope runoff sites. The simulations are also consistent with process interpretations from hydrogeochemical observations using natural chloride and stable isotopes at the site. Spatial analysis of the hillslope simulations reveal that vegetation and terrain curvature have strong controls on soil moisture and runoff generation during different periods. In particular, we quantify a temporal switching from vegetative to topographic controls as a function of antecedent wetness during summer periods with high rainfall amounts. The coarsening of model resolution eliminates small-scale topographic features which reduce the impact of lateral fluxes on the resulting spatial patterns. On the other hand, model coarsening has a more limited impact on vertical fluxes controlled by the larger-scale vegetation patterns, but still distorts the spatial soil moisture distribution during specific periods. By using a patchiness metric, we find that model coarsening increases the size of soil moisture features at the hillslope scale and relate this to the aggregation properties of the underlying fields. Finally, we discuss the study implications on the design of hillslope-scale characterizations and observation networks.
Mahmood T.H., Vivoni E.R. (2010): Transition of spatial controls on distributed soil moisture and runoff simulations at multiple model resolutions . AGU Fall Meeting (Poster) Abstract H41F-1133..