Impact of slope, aspect and cloud cover on the distribution of incoming global solar radiation over Pakistan

We use a distributed modeling approach to investigate the spatial and quantitative distribution of incoming global solar radiation (GSR) falling over the complex terrain using remote sensing (RS) and geographical information system (GIS). To apply distributed model, we use SRTM digital elevation models (DEM) for impact assessment of slope, aspect orientation and correcting possible sunshine duration over the inclined surface. Similarly, to evaluate the impact of cloud cover on incoming global solar radiation amount and spatial distribution, we use MODIS Level-2 (L2) cloud fraction products and observational data of cloud cover from 21 meteorological observatories in Pakistan. As an input for incoming GSR model, the direct, diffused, and terrain reflected components of GSR were employed. The model results show clear quantitative influences of local topography based on slope angles and cloud cover variations on the distribution of GSR in the North and Northwest of Pakistan. Similarly, slope and aspect influences are evident over the mountainous areas in Himalaya, Karakorum and Hindukush Ranges in North and Suleiman Ranges in Northwest. Furthermore, terrain effect for eastern and western slopes is not significant; the slopes receive almost the same radiation due to the orientation of topography and latitudinal consistency, but inter-shielding effect in eastern-western oreintation is more prominent compared to the one in northern-southern.