Time dynamic pollution risk modelling of groundwater at the pan-African scale

Groundwater vulnerability mapping is an important key for improving the planning and decision making processes in order to prevent groundwater contamination. To this regard, we filled a significant knowledge gap on groundwater pollution at the continental scale of Africa by developing method for assessing groundwater pollution risk at the pan-African scale (Ouedraogo et al., 2016) based on a “static” hypothesis. However, some of the parameters taken into account by this method may vary over time such as recharge, groundwater level, land use, etc. In the present work, through the application of the DRASTIC method to evaluate the intrinsic vulnerability at the African scale, and using the most recent continental scale data on soil, topography, land use, geology, hydrogeology and climate in a Geographical Information System at the resolution of 15x15 km2, we showed that groundwater vulnerability to pollution varies from one year to another, i.e. that it is dynamic. For this, we compared the years 1990, 2000 and 2010 selected for their different land use by using Density of population (D) as a proxy for this land use. These years are chosen according to their data available to incorporate time dimension in the vulnerability modelling. The elaborated vulnerability maps show variability in the spatial distribution of vulnerability degrees between the three years. The maps reveal that areas of Nile Delta, areas around the Lake Victoria, North Africa, and coastal in West Africa changes from one map to another. The highly vulnerable areas have increased in relation to the increase of the density of population. The temporal groundwater vulnerability proposed in this study, would constitute a new approach allowing vulnerability dynamic mapping. This can provide an important tool for the sustainable groundwater resources management in Africa, and participates indirectly to achieve SDG Goal 6 which includes a focus on preserving our freshwater resources for potential future threats