Using sub-grid-scale topographic information to parameterise a probability-distributed runoff-production scheme for regional climate modelling

Fully-coupled regional climate models require the representation of hydrological pro- cesses at spatial scales coarser than the scale over which topographic variability influ- ences water fluxes. It is possible to retain sub-grid-scale information by constructing a parameterised representation of fine resolution topography. Here we describe a procedure that can be used to infer catchment and grid-pixel hydro- logical properties from existing topographic and geomorphic datasets. This procedure permits the calculation of the probability distribution of soil moisture stores within a grid pixel or a catchment. The new scheme is demonstrated in use as a hydrological sub-component of a regional climate/land-surface model. As well as improving the representation of hydrological processes in coarse resolution gridded flow models, the work may provide a physically-based method of providing enhanced calibration of hydrological models in ungauged basins using readily available geomorphic data.