Quantifying the overlooked groundwater component in the water budget of a shallow soda lake in Hungary amidst climate change concerns

Study region: Lake Velence. Study focus: Soda lakes are extreme habitats whose special hydrochemical characteristics can partly be explained by groundwater inflow. The relationship between groundwater and Lake Velence has never been properly investigated. A significant decrease in the lake's level in recent years urged an evaluation of the components of the lake's water budget, including groundwater as well. A 3D transient numerical groundwater flow simulation, using Visual MODFLOW, was performed between 1990 and 2021 to evaluate the lake's relationship with groundwater and quantify the groundwater discharge into the lake. To assess future lake level changes until 2050, six lake level simulations were run based on three different regional climate models and two global warming scenarios (RCP2.6 and RCP8.5). New hydrological insights for the region: Our results showed that groundwater inflow accounts for up to 12 % of the total annual inflow into Lake Velence. It has been numerically shown that precipitation and evaporation are the primary drivers of lake level changes, meaning that the variation of these two parameters will impact the lake's future. As for the future lake level changes, the RCP2.6 scenario resulted in an increase of 11 cm, while the RCP8.5 scenario led to a decrease of 30 cm compared to the observed annual average lake level until 2050. Our results emphasize the importance of integrating soda lakes into topography-driven groundwater flow systems to develop climate change adaptation strategies.