title: Linking Surface Urban Heat Islands with Groundwater Temperatures.
abstract: Urban temperatures are typically, but not necessarily, elevated compared to their rural surroundings. This phenomenon of urban heat islands (UHI) exists both above and below the ground. These zones are coupled through conductive heat transport. However, the precise process is not sufficiently understood. Using satellite-derived land surface temperature and interpolated groundwater temperature measurements, we compare the spatial properties of both kinds of heat islands in four German cities and find correlations of up to 80%. The best correlation is found in older, mature cities such as Cologne and Berlin. However, in 95% of the analyzed areas, groundwater temperatures are higher than land surface temperatures due to additional subsurface heat sources such as buildings and their basements. Local groundwater hot spots under city centers and under industrial areas are not revealed by satellite-derived land surface temperatures. Hence, we propose an estimation method that relates groundwater temperatures to mean annual land-surface temperatures, building density, and elevated basement temperatures. Using this method, we are able to accurately estimate regional groundwater temperatures with a mean absolute error of 0.9 K.
authors.affiliation: Karlsruhe Institute of Technology (KIT) , Institute for Applied Geosciences (AGW), Kaiserstr. 12, 76131 Karlsruhe, Germany.
authors.forename: Susanne A
authors.initials: SA
authors.lastname: Benz
authors.affiliation: ETH Zurich , Department of Earth Sciences, Sonneggstr. 5, 8092 Zurich, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Bayer
authors.affiliation: Karlsruhe Institute of Technology (KIT) , Institute of Meteorology and Climate Research-Atmospheric Trace Gases and Remote Sensing (IMK-ASF), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Goettsche
authors.affiliation: Karlsruhe Institute of Technology (KIT) , Institute of Meteorology and Climate Research-Atmospheric Trace Gases and Remote Sensing (IMK-ASF), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Folke S
authors.initials: FS
authors.lastname: Olesen
authors.affiliation: Karlsruhe Institute of Technology (KIT) , Institute for Applied Geosciences (AGW), Kaiserstr. 12, 76131 Karlsruhe, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Blum
mesh_terms: D002947:Cities; D005858:Germany; D060587:Groundwater / Q000737:chemistry*; D006358:Hot Temperature; D018709:Statistics, Nonparametric