GEOSPATIAL ANALYSIS OF MEAN ANNUAL AND MONTHLY RAINFALL IN SAUDI ARABIA

Accurate estimates of annual and monthly rainfall at ungauged locations are required for spatially distributed hydrologic modeling, soil erosion control and energy balancing. Estimates of mean annual and monthly rainfall at ungauged locations in Saudi Arabia were obtained from sparse station data by univariate and multivariate spatial interpolation techniques using ArcGIS Geostatistical Analyst. Due to the strong correlation of elevation with annual and monthly rainfall in Saudi Arabia, digital elevation model were introduced as exhaustive ancillary data to augment the accuracy of the spatial interpolation process. Both annual and monthly rainfall exhibited very strong spatial continuity with the spherical model providing the best fit. Based on cross-validation technique, colocated cokriging provided the most accurate spatial interpolation and thus it was used to grid both annual and monthly rainfall data. Mean annual and monthly rainfall surfaces obtained by colocated cokriging are not only the most accurate, but also the least smoothed ones and depict clearly the local spatial patterns and regional trends.