A BOKU study shows how climate change and surface sealing are creating underground heat islands – with consequences for ecology, water quality, and geothermal energy. 

Climate change doesn't only make itself felt through extreme weather events – groundwater is affected too. Particularly in cities, a steady rise in temperature is measurable: in Vienna, the average groundwater temperature rose by 0.9 degrees Celsius between 2001 and 2010, and by as much as 1.4 degrees between 2011 and 2020. This shows that the rise in groundwater temperature is not occurring in a linear fashion. "This trend urgently needs to be taken into account in water management in order to avoid potential negative impacts on water quality and ecology," stresses Eva-Florina Kaminsky from the Institute of Soil Physics and Rural Water Management at BOKU. 

Particularly striking is the temperature difference between urban areas and the surrounding countryside: in sealed zones, groundwater is on average around four to eight degrees warmer on an annual basis – a phenomenon known as an underground heat island. The main cause is dense surface sealing: asphalt, concrete, and buildings store heat and conduct it into the ground. In addition, extensive underground infrastructure contributes to the warming – for instance through underground and road tunnels, underground car parks, sewers, district heating pipes, and geothermal cooling systems.

A recent study by BOKU University in cooperation with the University of Vienna and GeoSphere Austria has for the first time translated these temperature trends into high-resolution, area-wide maps. This has made underground heat islands visible and allowed their effects on the chemical composition of groundwater to be examined in detail.

Full details of the study at: boku.ac.at