Impact of climate change on the severity and recurrence of droughts in Iran

The objective of this paper is to assess quantitatively the potential recharge of shallow aquifers in the Senegal River delta in context of semi-arid climate, of massive irrigation development and of modification of hydrologic and hydrogeological characters after dams building. Quantitative estimation of recharge potentialities have been based on hydrological balance and groundwater table fluctuation calculations and on isotopic tracers techniques of the water molecule (δ18O, δ2H and 3H). This different methodological approaches used to estimate recharge rates have been useful, valuable and complementary. They give results fairly homogeneous and very interesting with indications accurate enough on recharge rates and on recharge spatio-temporal variations in shallow aquifers in alluvial plain (rate varying between 0-37% of annual rainfall) and dunes formations (rate varying between 0-44% of annual rainfall). Results indicate that recharge variations in term of proportions and of distribution are not only depending of volume and frequency rainfall or groundwater depth but also depending of soil and subsoil surface conditions, human activities (water withdraw, irrigation, market gardening, etc.) and evaporative demand. This recharge knowledge in terms of proportions and distribution in shallow aquifers is often very useful to propose groundwater resources management model and to define strategies to exploit them sustainably especially when groundwater resources are very unproductive and often very salty as in Senegal River delta.