Previously drilled boreholes of a host rock for a potential nuclear waste repository in Hungary revealed a highly fractured claystone rock body. A crucial step for characterizing the hydrodynamic behavior of such a fractured reservoir is fracture identification and accurate calculation of the fracture density. Although acoustic borehole televiewers provide a reliable base for determining the fracture density, older boreholes usually lack such data. However, conventional borehole geophysical measurements are often accessible in such cases. The aim of this study was to identify any correlations between well log data and fracture density. Multiple linear regression analysis was performed on data from two boreholes penetrating the Boda Claystone Formation in southwest Hungary. The upper section of the BAF-4 borehole was used for training, where the fracture density was estimated with a fit of R² = 0.767. The computed regression function predicted the fracture density with high accuracy in both boreholes for all intervals with typical lithological features. However, in some sections where anomalous well log data indicated changes in the lithology, the prediction accuracy decreased. For example, the function underestimated the fracture density in sandy intervals.

The fracture network modelling and hydrogeological assessment were performed in an 845 m deep borehole of the potential high-level waste repository formation and its caprock. The geometry of the fracture network was simulated using the discrete fracture network (DFN) modelling method, which is based on the geometric characteristics of the individual fractures. The hydrogeological evaluation was based on changes in porosity and permeability along the borehole using flow zone indicator (FZI) values that denote hydraulic flow units (HFU) within the rock body. Fracture network characteristics and hydrogeological features are mainly determined by the wellbore lithology, which can be divided into three zones. The sandstone body was intersected in the upper 300 m of the borehole, which forms a single HFU. The second zone was developed along with the transition zone between the sandstone and the underlying claystone bodies. Here the predominant rock type is claystone, but the characteristics of the fracture network are distinctly different from the deeper parts of this rock body. Below 400 m is the third zone, where distinct and extensive HFU-s could not form, probably due to different water–rock interaction processes that could have changed the porosity and permeability from point to point in the claystone.

A Nyugati-Mecsekben elhelyezkedő Bodai Agyagkő Formáció (BAF) a nagy aktivitású radioaktív hulladékok elhelyezésére szolgáló mélygeológiai tároló potenciális befogadó képződménye. Mivel a BAF porozitása és permeabilitása extrém kicsi, így abban fluidumáramlási útvonalak törések, szerkezeti inhomogenitások mentén jöhetnek létre. Ebből adódóan kiemelkedően fontos a BAF deformációtörténetének megismerése, melyről a repedések, repedésrendszerek hordoznak információt. Kutatásunk során a Boda község közelében mélyült BAF–2 fúrás 74,34–899,22 m közötti mélységtartományából származó 56 db fúrómagminta szerkezeti elemeinek morfológiai és ásványtani vizsgálatát végeztük el, továbbá az érkitöltések belső mikroszerkezetét értelmeztük. Az egyes repedésgenerációk cementfázisainak összetételét polarizációs mikroszkópos megfigyelések, röntgenfluoreszcens spektrometria és Raman mikrospektroszkópia segítségével elemeztük. A magpalástról készített felvételek alapján az ereket 22°, 42° és 70° átlagos dőlésszögű csoportba soroltuk. A repedéskitöltéseket ásványtani alapon két kategóriába osztottuk. Az első kategóriába sorolható erek dominánsan kalcit kitöltésűek, azonban a másodlagos repedéskitöltő ásványtársulások mintánként eltérően albit, albit-cölesztin, valamint kvarc-pirit lehetnek. A vizsgált repedéskitöltések második csoportjában kalcit-anhidrit a domináns kitöltő ásványegyüttes, amely mellett másodlagosan kvarc-barit-cölesztin, valamint albit-pirit-cölesztin jelenik meg. A repedéskitöltések szöveti elemzése során szintaxiális, antitaxiális és ataxiális növekedési morfológiával rendelkező ereket különböztettünk meg. Az ásványtani alapon közös kategóriába sorolható értípusok orientációbeli, valamint szöveti tulajdonságaik alapján azonban markánsan eltérő deformációs-és fluidumáramlási eseményeket jeleznek.

Climate change is increasingly affecting groundwater resources in the Carpathian Basin, and rising temperatures are expected to increase irrigation demand and pressure on aquifers; the Nyírség region in north-eastern Hungary, a hydraulically coherent recharge–discharge system, provides a suitable setting to investigate these impacts. We analysed multi-decadal groundwater levels from shallow monitoring wells (1970–2022) together with hydroclimate indicators derived from CHIRPS precipitation and ERA5-Land snow and temperature data (1981–2024). Using these inputs, we developed a MODFLOW groundwater flow model for the study area and calibrated it for representative drought and rainy periods, explicitly incorporating permitted withdrawals and estimates of illegal pumping, and applied scenario simulations to assess expected mid-century (2050) climate conditions and human-driven changes, including managed aquifer recharge options. The hydroclimate indicators show strong interannual precipitation variability alongside an overall warming and drying tendency and reduced snow storage. Scenario runs indicate declining shallow groundwater levels, with the largest decreases in higher-elevation areas, while increased pumping primarily intensifies local drawdown near major well fields. Model results suggest that direct subsurface injection is the most effective recharge approach, and water-budget analysis indicates that natural variability can drive subsurface flow changes much larger than those caused by water production, underscoring the need for integrated, long-term measures that include changes in water use.

Climate change is increasingly affecting groundwater resources in the Carpathian Basin, while rising temperatures are likely to increase irrigation demand and pressure on aquifers. We assessed climate- and pumping-driven impacts on the Nyírség recharge–discharge system (north-eastern Hungary) by combining shallow groundwater monitoring (1970–2022) with hydroclimate indicators from CHIRPS precipitation and ERA5-Land air temperature and snow depth (1981–2024). Using these datasets, we developed and calibrated a MODFLOW groundwater-flow model for representative wet (2010) and dry (2022) conditions, incorporating permitted abstraction and scenario-based estimates of unregistered pumping. We then ran scenario simulations to evaluate mid-century (2050) conditions and managed aquifer recharge (MAR) options. Precipitation exhibits strong interannual variability, but the region shows marked warming and a pronounced decline in snow storage, implying reduced cold-season buffering and higher evaporative demand. Simulations reproduce the observed post-2010 decline in shallow groundwater, with the largest decreases in higher-elevation recharge areas, whereas increased pumping mainly intensifies localized drawdown near major well fields. Scenario results indicate that climate-driven reductions in recharge dominate basin-scale declines by 2050, while MAR provides primarily local benefits; direct subsurface injection performs best among the tested options. These findings support practical groundwater management by prioritizing measurable and enforceable abstraction (including unregistered withdrawals), demand-side irrigation efficiency and adaptive caps in recharge areas, and targeted subsurface MAR where source water and infrastructure are available.