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Accueil du site → Doctorat → Allemagne → 2008 → Estimation of groundwater recharge in the context of future climate change in the White Volta River Basin, West Africa

Rheinischen Friedrich-Wilhelms-Universität Bonn (2008)

Estimation of groundwater recharge in the context of future climate change in the White Volta River Basin, West Africa

Obuobie, Emmanuel

Titre : Estimation of groundwater recharge in the context of future climate change in the White Volta River Basin, West Africa

Auteur : Obuobie, Emmanuel

Université de soutenance : Rheinischen Friedrich-Wilhelms-Universität Bonn

Grade : Doktorgrades (Dr. rer. nat) 2008

Résumé The White Volta River Basin is one of the major sub-basins of the Volta River Basin of West Africa. It covers about 106,000 km2 , and the major riparian countries are Burkina Faso and Ghana. The basin has enough water resources to meet current demands but there are many challenges including high spatial and temporal variability in rainfall, global climate change, deforestation, land degradation, and high population growth rate. These challenges put immense pressure on the water resources. The basin experiences a prolonged dry season when many rivers and streams dry up. As a result, surface water supplies are unreliable and insufficient to meet the water demands for socio-economic development in many places in the basin, thereby making groundwater sources the preferred and most cost-effective means of supplying water to the largely rural and dispersed population in the basin. A key prerequisite for efficient and sustainable management of the groundwater resource is the understanding and quantification of the groundwater recharge. This study estimates the total amount and spatial distribution of the groundwater recharge at different scales in the White Volta Basin using the chloride mass balance, water table fluctuation, and hydrological modeling with the Soil and Water Assessment Tool (SWAT). In addition, the study evaluates the impact of future climate change on the shallow groundwater recharge. The chloride mass balance method was applied in the northeastern part Ghana (Upper East Region of Ghana), within the basin, to estimate the long-term recharge. Based on the variation of chloride concentrations measured in groundwater samples taken from 11 wells in 2006, the estimated long-term annual groundwater recharge in the region ranged from 34.0 to 182.0 mm, with an area-weighted mean of 82.0 mm. The mean annual recharge represents 8 % of the long-term mean annual rainfall of 990 mm. The water table fluctuation method was used in the south of the basin (commonly called the White Volta Basin of Ghana) to evaluate the seasonal and annual variations in water level rise and to estimate the groundwater recharge. The results show that annual water level rise ranged from 1238 to 5000 mm in 2006 and from 1594 to 6800 mm in 2007. Based on standard values of specific yield and the measured water level rise, the estimated annual recharge ranged from 28.0 to 150.0 mm in 2006 and from 32.0 to 204.0 mm in 2007. The area-weighted mean recharge was 70.0 mm in 2006, representing 8 % of the annual rainfall (870 mm), and 92.0 mm in 2007, representing 7 % of the annual rainfall (1294 mm). The SWAT model was calibrated (1986-1999) and validated (1992-1999) at Nawuni for the whole White Volta River Basin. The simulated mean recharge to the shallow groundwater was 59.0 mm, about 7 % of the mean annual rainfall (824 mm). Using SWAT-simulated water balance for the present time period (1991-2000) as the basis for comparison, the simulated future (2030-2039) water balance in the White Volta Basin shows important increases in the mean annual discharge, surface runoff and shallow groundwater recharge as a result of future climate change in the basin. The shallow groundwater recharge is expected to increase by about 29 %.

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