Spatial interpolation of rainfall in the dry zone of Sri Lanka

One of the problems which often arises in climatology is either data at a given site is missing or the site is ungauged. In this study, a spatial interpolation model was developed to estimate the weekly rainfall of the Dry zone of Sri Lanka at ungauged sites assuming that the spatial continuity of rainfall at two neighbouring locations are exponentially correlated. Twenty years of weekly rainfall data from six stations located in the Dry zone was used in the study. To support the methodology, the results of the exponential model were compared with the other two methods of spatial interpolation techniques, namely, the local mean and the inverse distance methods. The results of the study indicates that the exponential correlation model is a promising candidate for estimating mean weekly rainfall of the Dry zone. However, the local mean and the inverse distance methods compare quite well along with the exponential model, indicating that more complex models have no particular advantage over simple models for estimating rainfall in the Dry zone of Sri Lanka. Nevertheless, the results point towards the relative importance of the exponential model as opposed to the other two models when the neighbouring locations do not have long series of historical records