The Impacts of Change in Rainfall and Groundwater Withdrawal on Groundwater Resources of Raya Valley, Northern Ethiopia.

English Abstract:

Climate change and anthropogenic factors have direct impact on the availability of subsurface water. Groundwater potential is governed by its quality and the quantity. The groundwater quantity is interconnected with the hydrological cycle and its components. Change in climate condition will have impact on the hydrological cycle leading variability on the groundwater resource by affecting the groundwater recharge. In contrary, human impact like excessive pumping exacerbate the depletion of the groundwater potential. In this study, we give more emphasis to change in rainfall and human induced groundwater discharge, on the available groundwater resource.

We have conducted hydrological and hydrogeological study to see the impacts of change in precipitation and groundwater withdrawal using groundwater flow modeling in Raya Valley, Northern Ethiopia. Raya valley, is characterized by humid to semiarid climate condition, where surface water is limited. The hydrogeological studies had proven the groundwater is accessible along two major aquifers, these are fractured volcanic and alluvial aquifers. Geomorphological setup shows, the volcanic aquifer is situated in the humid highland area and the alluvial aquifer is found in the lowland, where the climate condition is semiarid. The major sources of water are groundwater and seasonal flooding water.

A comprehensive conceptual modeling of the basin has been carried out using hydrochemistry, isotope hydrology, and hydrogeological studies. Then we conducted the flow modeling using Modflow Pro. The model was calibrated with the actual hydrogeological condition. The model result depicted that change in rainfall have a general declining trend in water level, this is as a result of reducing groundwater recharge. Under this scenario, lowering lake level and drying up of swampy areas is observed. The simulation of increasing groundwater pumping from the aquifers have been done to predict future water use and its impact. The model results shows that, a dramatic groundwater fall up to 20 meters as a result pumping ten times the current groundwater withdrawal. Therefore, the groundwater potential of the basin can be affected under high pumping conditions and the adjacent wetlands will dry up, as a result of pumping the groundwater dependent ecosystem will be in danger.