This paper evaluates numerically the effects of climate change (precipitation, temperature, and sea level rise (SLR)) on two selected coastal aquifers located in the north of Oman: (1) Jamma aquifer which is mainly used for irrigation and (2) Samail Lower Catchment aquifer (SLC) which is a strategic reserve for domestic water supply, hence it is of great economic value. Unlike Jamma aquifer, SLC maintains positive gradient seaward as the aquifer is currently well-managed. The water dynamics in both aquifers are studied numerically using MODFLOW and MT3DMS codes under the different Representative Concentration Pathway scenarios (RCPs) for years 2050 and 2070 according to the Intergovernmental Panel on Climate Change (IPCC). Results show that the salinized area in Jamma site, considering the intruded distance of the selected 1500 ppm iso-concentric line, will increase by 32 and 38% by years 2050 and 2070, respectively, compared to the situation for the base case year 2015. This effect is significant given the narrow agricultural strip area it covers which is also shared for urban and industrial land uses. Hence, the farming community will be severely affected. The positive hydraulic gradient seaward direction for SLC aquifer (because of proper management) helps to combat significant intrusion of saltwater. In general, the results show rapid climate change impacts during the next 15 years which urges implementation of measures to reduce the effect, before the farming community at large (along with other users) be severely affected and adaptation measures become infeasible. SLR was found to be the main climatic factor that will significantly affect the stressed coastal aquifers. The change in rainfall rate for north of Oman is small and the effect of evapotranspiration is relatively low given the high extinction depth (deep water table) and sparse vegetation. The extent of the effect of climate change on aquifers is site specific. Stressed aquifers like Jamma are highly vulnerable and severely affected. Alleviation of the impact and adaptation measures must be planned first for more vulnerable aquifers. The adaptation measures should include managed aquifer recharge using both ephemeral floods generated by irregular and limited rainfall events and by using treated wastewater, expanding in reuse of treated wastewater, and improving the efficiency of irrigation (main consumer of available water, > 80%) along with better water pricing policies. Although the currently well-managed aquifer systems (e.g., SLC) are not significantly affected by climate change, improper development and management of those systems would definitely shift them to be more vulnerable to adverse effects of climate change. The findings of this study are importance for the water resources managers as they stressed that precaution measures must be implemented for the deteriorated aquifer (like Jamma aquifer) while protecting and maintaining the well-managed groundwater systems (e.g., SLC aquifer) as these show more resilience to climate change. Efforts should be devoted to manage stressed aquifer systems as a priority in order to improve their resilience level to climate change.
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