Dynamic Recharge Thresholds in MODFLOW for Assessing Climate Change Impacts on Arid Aquifers

الملخص

Water recharge in dry conditions is non-persistent, threshold-related, and strongly influenced by soil moisture dynamics; however, traditional modelling techniques, such as calculating recharge coefficients in conventional MODFLOW, produce inaccurate results because they do not capture these non-linear process characteristics. The presented work builds and validates a physics-based model by incorporating dynamic soil moisture–rainfall feedbacks into MODFLOW-6 to enhance the accuracy of recharge estimates in climate-sensitive areas that lack sufficient water. The technique, which combines HYDRUS-1D simulations with MODFLOW-6, uses an application programming interface through which Richards equation-based recharge thresholds are applied and respond to real-time soil moisture conditions. In Libya, the framework was implemented in the Tripoli and Kufra Basins under both historical (1980–2020) and future climatic conditions (SSP2-4.5 and SSP5-8.5). The feedback-based methodology eliminated systematic overestimation of recharge by 40–60 per cent compared with static and soil-water-balance methods and was in close agreement with the chloride mass balance data. Under high-emission conditions, recharge decreased by 23–41 per cent despite increased precipitation, due to amplified evaporative demand and longer dry periods. This paper operationalises soil moisture thresholds as climate-reactive controls in operational groundwater models to offer a transferable instrument for sound aquifer vulnerability analysis and climate-adaptation planning in dry areas of the world.