Objective assessment of the Thiessen polygon method for estimating areal rainfall depths in the River Volta catchment in Ghana

Abstract

Among the problems facing hydro-meteorologists and climatologists is the estimation of rainfall depths at places where there are few or no rainfall stations. A number of models have therefore been developed, evaluated, and recommended by eminent hydrologists and climatology for their applications. These applications are related primarily to specific problems and for the purpose of identifying the most suitable methods for estimating rainfall depths in river basins with very few rainfall records or stations. In this paper, the applicability of the Thiessen polygon method has been reviewed and employed for the purpose of estimating rainfall depths in the River Volta catchment in Ghana. A regression statistic performed to establish the effect of elevation on rainfall distribution in the catchment shows that the former has little or no effect on the latter. The review of the Thiessen method and the results of the analysis of the rainfall field using the polygons show that the method is suitable for estimating rainfall depths in the River Volta catchment in Ghana. The recommendation, however, is that the rain-guage network in the catchment should be improved in other to obtain more but smaller polygons, showing distributions in smaller areas.