Isotope Hydrology progress in sub-Saharan Africa. What information for water management? 

Abstract

The utility of isotope techniques in hydrological investigations stems from their ability to label water sources and cycling processes including surface/groundwater interaction, water residence times, flow pathways, evaporation fluxes, and solute processes, to name a few. In Africa, they have been applied since four decades following the severe drought of the 1970s, and can now be summarized in important case studies. This review focusing on Cameroon (often called the little Africa) aims to put together all the stable and radioactive isotopic data (>500 samples from rainfall, surface and groundwater) published in the country to: (i) identify the drivers responsible for precipitation isotopes spatial variation and climatological implications, (ii) elucidate the groundwater recharge mechanisms over the countries and relationships with rivers, and (iii) highlight the existence of paleo-groundwater in the country. It is found that rainfall stable isotopes variation is linked to the migration of the Intertropical Convergence Zone (ITCZ). The groundwater recharge can be diffuse and focused. This latter mechanism is mainly observed in the semi-arid region. It is in this relatively dry region that most of the paleo-groundwater resources are identified thanks to 14C dating. This information will be useful to develop water management strategies regarding all the challenges (e.g., climatic and demographic) faced by the country. Finally, this paper discusses the gaps groundwater isotope hydrology can still fill for contributing to a sustainable development of the country. Reflections provided here can be extend in each country of the sub-Saharan Africa region.