Groundwater in north and central sudan

North and Central Sudan represents the hydrogeological interface between the sedimentary Blue and White Nile Basins and the large Nubian Aquifer System of North Sudan. The average annual precipitation increases from north (<50 mm) to south (380 mm). Stable isotopes of =320 water samples reveal three possible mechanisms of groundwater recharge: a) natural recharge along wadis and in lowlands during floods, b) man-induced infiltration of irrigation water, and c) natural river bank infiltration along rivers. Groundwater more than 25 km away from rivers carries the isotopic signature of ‘palaeo-groundwater’ in many places. Since the Early Holocene ‘climatic optimum’, direct recharge by precipitation is considered as negligible in the northern region. In the southern region of the investigated area there are indications of a modern recharge. However, the spatial significance and the quantity are unknown and further research is needed. The biggest challenges for the future are quantifying the available renewable resource and managing groundwater abstraction sustainably.