Groundwater recharge and climate change effects (GRaCCE); Quantification of resilience of water resources in carbonate aquifers to drought conditions; Collaboration between Palestine, Israel & Jordan within the context of the BMBF-Research Program: "Wasserforschung im Nahen und Mittleren Osten - Modul A"

Abstract

The Western Middle East is under severe water stress, exacerbated by political tension and transboundary water issues. Carbonate karst aquifers are widely distributed across this region and form a critical component of the freshwater resources. These aquifers, characterized by fractured and porous media, serve as essential resources of drinking and irrigation water in semi-arid areas such as Israel, Palestine, and Jordan. Due to the presence of preferential flow paths, generally low storage coefficients, and limited buffering capacity, karst systems are particularly susceptible to drought conditions. Sustainable water management in karst settings requires not only reliable data on the volume of water stored in the subsurface but also an improved understanding of the spatiotemporal variability of climate and recharge processes. Key karst aquifers in this region are shared between Israel, Palestine, and partially Jordan, creating both technical and diplomatic challenges for water governance. Moreover, strong seasonal and interannual hydrological fluctuations, and high evaporation losses from one side, and insufficient wastewater treatment on the other side, together contribute to groundwater overexploitation and water quality deterioration. The demand on water resources is further intensified by industrial development and population growth, including migration from conflict-affected areas. The GRaCCE (Groundwater Recharge and Climate Change Effects) project addresses these challenges by developing a process-based, integrated approach for determining groundwater recharge and predicting climatological and hydrogeological drought events for long- and short-term time scales. The project focuses on the dynamics of fractured karst aquifers, where infiltration is highly variable and a challenge to model employing conventional techniques. Previous research by project partners has shown that thick vadose zones, of several hundred meters depth, can act as significant temporary storage reservoirs. These zones may function as dynamic water resources capable of buffering drought impacts. However, the dual-permeability nature of these systems-comprising rapid conduit and slower matrix diffusive flow - complicates the quantification of vertical water fluxes through the unsaturated zone. To address this, GRaCCE combines multiple disciplines and methods, including climate research, hydrogeological field characterization, geophysical and hydrogeochemical analyses, and advanced numerical modeling. These are complemented by surrogate models that allow efficient simulation of infiltration dynamics across management-relevant timescales. In addition, the project integrates high-resolution, daily-based climate model outputs that represent expected changes in precipitation and evapotranspiration until 2070 and beyond. These inputs enable robust scenario modeling and the identification of future water deficits based on validated drought indicators. The final output of GRaCCE is a web-based toolbox named "Drought Monitor" that includes a drought early warning system with adaptive water management strategies-specifically, optimized pumping and storage protocols. This platform can be expected to support decision-making by local authorities and water users, contributing to increased regional resilience against the effects of extreme climate events and long-term water scarcity. By improving the scientific basis for groundwater management and fostering cooperative solutions across political boundaries, GRaCCE aims at providing a transferrable model for water-stressed karst regions in the Middle East and worldwide.