title: Subsurface urban heat islands in German cities.
abstract: Little is known about the intensity and extension of subsurface urban heat islands (UHI), and the individual role of the driving factors has not been revealed either. In this study, we compare groundwater temperatures in shallow aquifers beneath six German cities of different size (Berlin, Munich, Cologne, Frankfurt, Karlsruhe and Darmstadt). It is revealed that hotspots of up to +20K often exist, which stem from very local heat sources, such as insufficiently insulated power plants, landfills or open geothermal systems. When visualizing the regional conditions in isotherm maps, mostly a concentric picture is found with the highest temperatures in the city centers. This reflects the long-term accumulation of thermal energy over several centuries and the interplay of various factors, particularly in heat loss from basements, elevated ground surface temperatures (GST) and subsurface infrastructure. As a primary indicator to quantify and compare large-scale UHI intensity the 10-90%-quantile range UHII(10-90) of the temperature distribution is introduced. The latter reveals, in comparison to annual atmospheric UHI intensities, an even more pronounced heating of the shallow subsurface.
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Applied Geosciences (AGW), Kaiserstr. 12, 76131 Karlsruhe, Germany. kathrin.menberg@kit.edu
authors.forename: Kathrin
authors.initials: K
authors.lastname: Menberg
authors.forename: Peter
authors.initials: P
authors.lastname: Bayer
authors.forename: Kai
authors.initials: K
authors.lastname: Zosseder
authors.forename: Sven
authors.initials: S
authors.lastname: Rumohr
authors.forename: Philipp
authors.initials: P
authors.lastname: Blum
mesh_terms: D002947:Cities; D002958:City Planning; D004784:Environmental Monitoring / Q000379:methods*; D055593:Geological Phenomena; D005858:Germany; D006358:Hot Temperature; D014507:Urbanization / Q000639:trends*