THE EFFECTS OF CLIMATE CHANGE AND URBAN WARMING ON GROUNDWATER TEMPERATURES AROUND THE GLOBE (Invited Presentation)

Climate change and urban warming are the driving forces behind changing atmospheric temperatures. Both of them affect the underground as well, where warming groundwater temperatures alter the geothermal potential, lower water quality, threaten groundwater dependent ecosystems and accelerate the thawing of permafrost. A study assessing 227 wells in Austria finds groundwater temperatures to increase on average by 0.7 °C in the last decade – an even faster rate than nearby air temperatures. Still, the impacts of climate change and urban warming on groundwater temperatures is so far under reported, particularly in large scale studies. A major obstacle is the lack of costly well or borehole infrastructure to observe them directly. Hence temperatures at more than 2,500 measurement points are compared to satellite derived land surface temperatures to reveal characteristic trends. A multi-variate regression accounting for latent heat in from of vegetation and insulation through snow cover is set up and models annual mean shallow groundwater temperatures globally (1-km resolution) with a coefficient of determination of 0.95 and a root mean square error of 1.4 K. However, the model is not set up to detect local temperature anomalies. These are often more than 6 °C warmer than their surrounding and caused e.g by underground infrastructure such as car parks, basements and district heating systems as revealed a large scale study of over 10,000 wells in ten European countries.