Lakes become bathtubs

Employees of the HUN-REN Balaton Limnological Research Institute (BLKI) analysed the changes in water temperature between 1870 and 2021 in relation to the larger lakes and rivers of the Pannonian ecoregion. They included water management data and their own data in their analyses. These were supplemented by calculated surface water temperature values based on satellite images and data from weather stations.

The most recent study showed that although the surface water temperature has warmed over the entire 150-year period, serious changes began in the second half of the 1980s: the rate of warming increased more than six-fold. Overall, the average increase in surface water temperature over the entire study period was 0.05°C per decade, but 0.32°C per decade over the last 40 years. Shallow lakes such as Lake Balaton, Lake Neusiedl and Lake Velence recorded a faster temperature rise of 0.46°C per decade compared to rivers, which warmed more slowly, by 0.27°C on average. Lake Velence warmed the fastest at 0.7°C every ten years. Interestingly, winter temperatures changed almost twice as fast as summer temperatures.

‘When the water temperature rises, the thermal balance of ecosystems is upset, which affects the species composition and stability of the aquatic environment,’ emphasised Viktor Tóth, senior researcher at the BLKI. Warmer water in shallow lakes can become a suitable habitat for invasive species. If the oxygen content of the water decreases, this can lead to more stress for aquatic organisms and change the water chemistry.