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Climate change impact in Western Africa: a sensitivity study for the Bani catchment

Congress: 2008
Author(s):
1rst author: Christel Prudhomme, Centre for Ecology and Hydrology, Maclean Building, Wallingford, OXON, OX10 8BB, UK, Tel: 0044 1491 692381, Fax: 0044 1491 692424, Email:C.Prudhomme@ceh.ac.uk 2dn author: Sandra Ardoin-Bardin, UMR HydroSciences Montpellie

Keyword(s): Climate change, IPCC, Bani, West Africa, Water resources
AbstractIn West and Central Africa, precipitation is scarce and unequally distributed throughout the year. In addition to the extensive deforestation and soil degradation, droughts and inundations often have dramatic consequences. Potential changes in the climate over the next century could accentuate the extreme flow fluctuation, and therefore must be better understood to improve water management. Global Climate Models (GCM) are the most reliable tools available to scientists to simulate the potential changes in the climate. However, the GCMs developed for the IPCC -2001 review were not always able to correctly reproduce the recent climate, particularly in Monsoon areas. The objectives of the paper are threefold, focusing on the catchment of Bani in West Africa: 1) to identify some of the biases in reproducing the recent climate of four GCMs developed for the IPCC-2007 review, and compare them with the IPCC-2001 GCMs outputs; 2) to assess how well the flow regime is reproduced from the new GCMs outputs using two gridded rainfall-runoff models; 3) to simulate future flow time series from future scenarios derived from the IPCC-2007 GCMs. The latest GCM outputs (developed for the IPCC- 2007 review) were obtained from the IPCC Data Distribution Centre. For each GCM, they consist of monthly precipitation and potential evapotranspiration (PE) series assuming (i) pre-industrial and recent past greenhouse gas concentrations in the atmosphere (GCM-control); (ii) greenhouse gas concentrations based on the SRES emission scenarios (GCM-future). The area of interest is confined to 17W-47E and 25N-45N. For this area, annual and monthly precipitation statistics obtained from the Climate Research Unit of the University of East Anglia (CRU) gridded time series are compared to GCM-control series for the models CSIRO-Mk2; ECHAM4; HadCM3 and NCAR-PCM. These GCMs were selected as their 2001 version had already been studied for the area of interest. The two conceptual hydrological models used, GR2M and GWAVA, were set up for the river Bani on the CRU 0.5x0.5 grid. Both estimate runoff at each grid from precipitation and PE, with a simple routing procedure distributing the discharge through the river network. Calibration and validation procedures exploit CRU precipitation and PE time series, and IRD flow series at Douna and Sofara. Other data include the FAO soil type and the USGS DTM. For both hydrological models, flow series obtained with CRU and all four GCM-control time series are compared to assess the bias due to GCM. Future flow series were obtained using precipitation and PE series derived from GCM scenarios and applying the factor (or delta) change perturbation method. Future simulations from different GCM are analysed and changes from the baseline period evaluated. Uncertainty due to GCM (both for the baseline and future periods) are compared to that due to hydrological modelling. Results provide an example of assessment of the quality of the most recent GCM simulations in West Africa, and discuss the impact of the latest climate change projections of the IPCC-2007 on the hydrology of the Bani. They will provide reference work for future impact studies in West Africa.
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