Calibration and evaluation of a semi-distributed watershed model of Sub-Saharan Africa using GRACE data

H Xie,L Longuevergne,C Ringler,B R Scanlon

doi:10.5194/hess-16-3083-2012

Abstract

Abstract. Irrigation development is rapidly expanding in mostly rainfed Sub-Saharan Africa. This expansion underscores the need for a more comprehensive understanding of water resources beyond surface water. Gravity Recovery and Climate Experiment (GRACE) satellites provide valuable information on spatio-temporal variability in water storage. The objective of this study was to calibrate and evaluate a semi-distributed regional-scale hydrologic model based on the Soil and Water Assessment Tool (SWAT) code for basins in Sub-Saharan Africa using seven-year (July 2002–April 2009) 10-day GRACE data and multi-site river discharge data. The analysis was conducted in a multi-criteria framework. In spite of the uncertainty arising from the tradeoff in optimising model parameters with respect to two non-commensurable criteria defined for two fluxes, SWAT was found to perform well in simulating total water storage variability in most areas of Sub-Saharan Africa, which have semi-arid and sub-humid climates, and that among various water storages represented in SWAT, water storage variations in soil, vadose zone and groundwater are dominant. The study also showed that the simulated total water storage variations tend to have less agreement with GRACE data in arid and equatorial humid regions, and model-based partitioning of total water storage variations into different water storage compartments may be highly uncertain. Thus, future work will be needed for model enhancement in these areas with inferior model fit and for uncertainty reduction in component-wise estimation of water storage variations.

Highlights

Sub-Saharan Africa (SSA) is used as a collective term that refers to African nations which lie south of the Sahara
The deterioration of its value is greater than two in models for all sub-regions other than West Africa, Nile and Zambezi when the parameter set in the Pareto frontier that most closely matches the simulation of Gravity Recovery and Climate Experiment (GRACE) total water storage (TWS) variations was used
The study presented in this paper concerns calibration/evaluation of a semi-distributed model based on Soil and Water Assessment Tool (SWAT) code (SWAT-SSA) for regional-scale hydrologic simulation in Sub-Saharan African countries

Summary

Introduction

Sub-Saharan Africa (SSA) is used as a collective term that refers to African nations which lie (or partially lie) south of the Sahara. The region makes up about 80 % of the African and 10 % of the global population. The agricultural productivity in SSA countries remains low relative to other parts of the world and the region is still beset with food insecurity. SSA is the only region where childhood malnutrition is projected to increase as a result of rapid population growth, climate change and continued low productivity in agriculture (Rosegrant et al, 2009). Annual population growth in SSA is 2.2 %, much higher than global average of 1.1 % (World Bank, 2009). SSA is regarded as the region with a low capacity to adapt to climate change (IPCC, 2007)

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