Spatial Interpolation of Annual Precipitation in South Africa-Comparison and Evaluation of Methods

Data from 545 rainfall gauges were used to interpolate the spatial distribution of annual rainfall in South Africa. Several spatial interpolation methods (inverse distance weighting (IWD), ordinary kriging, universal kriging, cokriging) were tested by variation analyses and cross-validation to determine the most suitable one. The best results were achieved by ordinary kriging, whereby the setting of the parameters was determined through sensitivity analyses. The median of the errors turned out to be 61 mm (11%). The interpolation errors were generally small for the interior of the country and high for coastal and mountainous regions.