The role of basin physical property data in assessing water stress in water resources studies: The application of the Pitman Rainfall-runoff model in Nigeria

Abstract

This paper examines the role played by basin physical attributes in determining river runoff. The approach uses soil and other available hydro-meteorological and geophysical information to directly estimate the parameters of the Pitman rainfall-runoff model to generate time series of historical and future hydrology of the basin. This study discusses the physical property information required, which includes basin soil texture types, depths, soil hydraulic and drainage properties, topographic slope and sub-surface geological conditions. FAO and available Nigeria soil maps provided a baseline of the requisite general soil information and other soil attributes information was inferred from literature. Owena, Asa and Ogun basins were used as case studies to evaluate the parameter estimation routines and the Pitman rainfall-runoff monthly model in Nigeria. Owena basin has some historical data, and based on the experience of using the model gained in this basin the approaches were then transferred to the ungauged basins of Asa and Ogun. While relative success was achieved in generating the hydrology of the test basins, it is suggested that the uncertainty related to the parameter estimation and the rainfall input be investigated and incorporated into the estimation process to provide a range of probable basin hydrology.