A contribution to the Einheitsfeier (celebration of the German reunification) in Halle an der Saale was provided by Peter Bayer with a talk on “Climate change beneath our feet“.
If the air warms up, over time the underground also gets warmer – in the end, the groundwater also warms up at a depth of a few meters. Unlike the atmosphere, however, the subsurface is rather inert. Therefore, it is a good indicator for climate change, because the subsurface does not react to short-term temperature fluctuations and thus more likely shows long-term trends. In our presentation, we report on the insight into the temperature development measured in numerous wells in Germany and worldwide. Groundwater is our most important source of drinking water and is constantly warming up. This is amplified by surface sealing, heat input from tunnels, civil engineering works, sewers and district heating pipelines. In the underground of large German cities, we now observe widespread temperature anomalies, so-called “urban heat islands in the underground”, which develop dynamically and, starting from the city center, spread both laterally and into depth This phenomenon can also be observed in many other cities around the world, especially in temperate and cold climates. Groundwaters in urban areas are therefore not only chemically but also thermally polluted. This combination is unfavorable, as the warming of groundwater may affect dependent ecosystems and lead to further mobilization of, for example, organic pollutants and heavy metals. In addition, there is the increasing thermal use of the subsurface by geothermal plants for heating, cooling and heat storage.