DISTRIBUTED ESTIMATION OF INCOMING DIRECT SOLAR-RADIATION OVER A DRAINAGE-BASIN

Because of topographic variability, the global flux of incoming direct solar radiation over a drainage basin of high relief should be evaluated by grid modelling. Alternatively, line integration throughout the catchment boundary can be substituted for areal integration over the detailed three-dimensional representation of basin topography. This method is based on the Stokes' theorem and it yields a general and efficient solution, which can also account for shadowing effects, Application to three small mountainous catchments is reported for varying solar geometry and the performance of a lumped model is also examined. The approach can be applied to estimate the contribution of shortwave radiative fluxes to the processes of snowmelt and evapotranspiration at the basin scale.