Estimation of spatial rainfall variability in a river basin from point rainfall data using GIS

Abstract

The rainfall data constitutes an input for water engineering resource management. This paper presents a study performed to establish the spatial variability of rainfall data from representative rainfall stations in an existing network in the Nairobi river basin. An attempt to solve the problem of estimating rainfall data at all points in a river basin from data obtained from a few representative stations using GIS. Rainfall data was acquired from the daily rainfall records of Kenya Meteorological Department (KMD) collected in a period of ten years. Rainfall stations were sampled for the study. The data was analyzed using spatial analyst in GIS. The following results were obtained; rainfall spatial averages and spatial average maps, rainfall variability pattern and predicting rainfall patterns. The number of representative rainfall stations is expected to reduce but still represent the basin in recording. Rainfall prediction can be drawn from the spatial variation maps for a given period of time. It can be concluded that the number of rainfall stations in the basin can reduce while still adequately recording a representative rainfall data and can be used to predict rainfall at any point in the river basin. The study recommends that the same technique be extended to other river basins. A further study on the relationship between the spatial rainfall distributions with changes in land use/cover and stream flows should be conducted.