Complex groundwater flow systems in the light of climate change: response of combined fluid driving forces on recharge reduction

Climate change induced alteration of recharge is expected to have diverse effects on groundwater levels, which could also modify the fragmentation and hierarchy of groundwater flow systems, including their dimensions and relative positions.

This study put emphasis on how flow system hierarchy may change due to recharge reduction in complex, vertically superimposed groundwater flow systems with different fluid driving forces through an example of the Duna-Tisza Interfluve in Hungary. Two main groundwater flow domain was identified by previous authors in this area with a separate source of water. Recharge to the upper, unconfined, gravitational regime is inferred to occur from infiltrating precipitation, while the underlying confined, overpressured flow domain is maintained by pore volume reduction due to tectonic compression of the basement (Tóth and Almási 2001, Almási 2003, Mádl-Szőnyi and Tóth 2009). The exposure of these groundwater flow systems, one is driven by gravity and other one is by overpressure, is completely different to the effects of changes in hydrologic parameters. Local scale gravity-driven flow systems are identified to be the most vulnerable to atmospheric processes (Kurylyk et al., 2014), while overpressured upward flow is driven by tectonic compression, and thus independent of climatic variation.

Two-dimensional transient numerical simulations were performed to gain insight into the response of this complex flow system to the predicted climate change of the region. Special emphasis is placed on i) how relative rate and influence of the different driving forces may change due to the predicted recharge reduction, ii) how the fragmentation of the flow field may alter, iii) how the penetration depth of upper, gravity-driven flow field may adjust to these changes and iv) how groundwater-related shallow surface water bodies will be affected by these changes.

Understanding the effects of changed hydrologic conditions on such complex flow patterns and recharge-discharge relationships as well as on interactions with surface water bodies can help to set-up three-dimensional site-specific models. These models provide a base to better mitigate and prepare for the consequences of predicted future changes.

The research is supported by the ÚNKP-20-4 New National Excellence Program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation Fund, as well as by the József and Erzsébet Tóth Endowed Hydrogeology Chair. This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.