Participating researchers:

Istvánovics, Vera; Berecz, Diána; Fülöp, Bence; Krámer, Tamás

Lake Balaton has been a regulated lake for over 150 years. Regulation tries to reduce the meteorologically driven level fluctuations of this large, shallow lake to an ever narrower range. This effort has been successful for decades by regulating only the drainage, due to the lake’s positive natural water balance.

However, it is expected that climate change will have a negative impact on the sustainability of the current water level management regime. This is due to the gradual disappearance of the natural water balance surplus until the end of the century. The lake is especially susceptible to changes in water levels caused by climatic fluctuations over the years, as it is shallow and has substantial infrastructure built for a stable water level.

The effect of climate change on the water balance of Lake Balaton has been a topic of concern since the drought of 2000-2003 and the subsequent decrease in water levels. Prior to the algal bloom in 2019, experts and the public alike viewed this issue as the most significant threat in the near future.

According to the water balance report from the local water authority, there were no years with a negative natural balance between 1921 and 1999, meaning that the water level of the lake did not decrease annually without any draining. However, since 2000, such years have occurred regularly. As a result, the control level was raised to conserve water for drier years. However, studies investigating the causes of the 2019 algal bloom have shown that high water levels can promote the persistence of thermal stratification. This, in turn, can lead to the development of large algal biomass due to the amplification of internal nutrient loads. This statement adds complexity to the issue of regulating water levels. The potential negative impacts of high water levels on water quality and riparian vegetation make it clear that a long-term solution cannot involve simply increasing the amount of water stored in the lake. Therefore, sustainable management must find a compromise between the competing priorities of water resources and water quality as climate change continues.

Water level regulation is not solely a geoscience or engineering issue. It is also crucial to meet the needs of water users and maintain the ecosystem services expected by them, given the intensity of lake use and its national and international significance. Furthermore, the needs of water users are evolving, partly due to past regulation and partly due to independent processes. The reaction to the drop in water levels during the 2000-2003 drought demonstrated that a change in the regulation regime is highly likely after significant dissatisfaction with water levels. Therefore, for water level regulation to be sustainable, it must align with current societal needs as well as scientific sustainability.

The basic research question is: “How can the water level of Lake Balaton be regulated in a sustainable way until 2060?”

Conflicts of interest often arise between climate-responsive water resource management, ecological needs, and the needs of water users. These conflicts cannot always be resolved based solely on scientific evidence. Therefore, the aim of this research is to develop a decision support system that can assist policy actors in designing a sustainable water stress management regime for a given period.