AbstractKarst aquifers can be particularly vulnerable to human activities and climate change due to their relatively high degree of connection with the surface. This study utilized an ensemble of event-based recharge calculation methods to address the problem of structural uncertainty for the example of the Western Mountain Aquifer (WMA), a Mediterranean karst aquifer located in Israel and the West Bank. Spatially distributed recharge estimates derived from the Soil and Water Assessment Tool (SWAT) and the process-based infiltration model (PIM) were compared to site-specific, empirical regression models. The SWAT and PIM mean annual recharge estimates ranged from 32–34.6% of precipitation, almost equating to the results of empirical regression models (32–36%). Future recharge predictions under the influence of climate change were quantified by parameterizing the SWAT and PIM methods with a downscaled regional climate model of Israel. SWAT predicts a 23% decrease in recharge by 2051–2070 relative to 1981–2001. In contrast, PIM shows a 9% decrease, possibly due to the representation of infiltration through preferential flow pathways and exclusion of surface runoff processes. These divergent projections underline key methodological differences in the representation of hydrological processes. Nevertheless, both methods effectively provided good estimates of groundwater recharge. The recharge rates estimated from the various methods were integrated into MODFLOW to assess their relative impacts on groundwater storage dynamics. The ensemble of MODFLOW projected groundwater storage outputs can provide guidance for sustainable groundwater management in the region.

Abstract Mine-water geothermal resources have potential to provide low-carbon heating and cooling in many areas; however, this potential has not been fully realised due to technical, economic and policy challenges. The UK Geoenergy Observatory (UKGEOS) in Glasgow was developed to provide an at-scale research facility designed to help de-risk mine-water geothermal usage. The limited knowledge of the hydrogeological systems altered by former mining activities is a key determinant of the long-term sustainability of water and heat abstraction/reinjection. This work presents a hydrogeological conceptual model developed using groundwater monitoring data obtained during the construction of the Observatory between 2020 and 2022, results from initial pumping tests performed in 2020, and results of hydrochemistry analysis from 25 sampling rounds collected between 2019 and 2022. The analysis of the data provides evidence of the dominant role of mine workings in controlling groundwater flow, with high intra-mine connectivity; increased fracturing in sandstones above mine workings; and limited inter-mine connectivity. Groundwater recharge is meteoric, mean residence times are >50 years, and there is a general upwards circulation from the deeper mine levels to the superficial deposits and the River Clyde. Faults play a significant role in limiting the extent of the highly transmissive mine workings, but there remains uncertainty surrounding the role of the faults in connecting different mine workings and their hydraulic behaviour in nonmined units. The conceptual model, that will be refined as new data become available, will be used to help guide monitoring and sampling programs and plan research activities in the Observatory.

AbstractFreshwater lenses and their freshwater–saltwater transition zones are affected by climate change. Both sea-level rise and groundwater recharge influence freshwater volume and transition zone thickness. This study used a semi-generic approach to investigate climate change effects on freshwater lenses: a hypothetical island cross-section was combined with real-world boundary conditions. Sea-level projections including tides and storm surges, annual mean sea-level rise data, and monthly recharge projections of several climate models of the German barrier island Norderney in the North Sea were used to evaluate changes in freshwater lens and transition zone size between 1971–2000 and 2071–2100. Firstly, impacts of sea-level and recharge boundary conditions were investigated on islands of different widths. Secondly, a multi-parameter study was conducted focussing on variations of several relevant hydrogeological parameters. Results showed that it is very likely but not certain that freshwater lens volume and depth will decrease and transition zone thickness increase as a consequence of climate change. Model predictions revealed a strong dependency on the employed climate models and to a lesser extent on the hydrogeological parameters, at least for the parameter ranges used in this study. Of all hydrogeological parameters tested, the largest effects were caused by the hydraulic conductivity and its anisotropy. Furthermore, the study showed that boundary conditions have larger impacts on smaller islands. These results illustrate the importance of using projections from climate models in a sufficiently high resolution. Furthermore, their uncertainties and changes in variability of boundary conditions should be considered in studies about climate change impacts on freshwater lenses.