Groundwater Annual Dynamics in the Basins of Woro and Chago (Eastern Niger) as Affected by Seasonal Variability and Anthropic Activities

The Sahelian region is known to have extremes climatic constraints since the end of the seventies. The studied zone is characterized by an extreme spatial and temporal variability of the environmental factors, complicating the understanding of the mechanisms governing the functioning of the hydrological system in the basin. The evapotranspiration was very high (1975 mm/an), whereas the local annual rainfall was around 300 mm/year. The piezometric data showed a rise of the groundwater level during the rainy season and a decrease in the dry season. The water balance obtained using the Penman-Monteith method showed the predominance of the evapotranspiration (75% to 80% of the rainfall) on the drainage (20% to 25% of the precipitations).