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Vergangenheit, Gegenwart und Zukunft von Urbanen Wärmeinseln im Untergrund von China und Deutschland - Konsequenzen für die geothermische Nutzung

Fachliche Zuordnung Hydrogeologie, Hydrologie, Limnologie, Siedlungswasserwirtschaft, Wasserchemie, Integrierte Wasserressourcen-Bewirtschaftung
Förderung Förderung von 2018 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 391979809
 
Erstellungsjahr 2023

Zusammenfassung der Projektergebnisse

The well-known urban heat island phenomenon also manifests underground in so called subsurface urban heat islands (SUHI). The scope of this project was to describe the processes and quantities of how SUHIs develop over time and which differences can be seen under different land cover types and climates in Germany and China. We reconstructed five decades of heat accumulation of a SUHI, which is triggered by anthropogenic heat emission and land cover changes like surface sealing, as well as by surface warming in response to climate change. It was also shown that the intensities of SUHIs cities varies substantially. To grasp and validate these processes numerical models were developed and lab experiments were conducted. Lastly the heat storage underneath our cities was quantified which yields a surplus in available energy for space heating with geothermal heat pumps, but also can pose a threat on groundwater quality and ecosystems. Major scientific advances have been achieved in the fields of SUHIs, climate change effects on the shallow subsurface, and management of shallow geothermal energy in cities. In the field of SUHI research that typically struggles from the lack of subsurface data we proposed and applied a new remote-sensing technique for estimating underground temperature in urban environments, and presented one of if not the longest continuous record of urban subsurface temperature monitoring. This revealed that heat accumulation over time is lower than estimated from expected heat fluxes from the surface. For example, the heat stored in the aquifer underneath Cologne could only provide 1% of the space heating demand of the city even though the accumulated waste heat, compared to natural conditions in the 1970s, could theoretically meet this demand for one year. Climate change in the shallow subsurface has been shown to be dampened (by about a quarter at 20 m depth) compared to the rise in near-surface temperature in rural settings. It was shown that these rural rates appear in a similar fashion also in the outskirts of the SUHI settings. However, in the city center warming rates in the subsurface can more than double the effects of climate change. Projecting these local findings to a global dataset we showed that recycling (waste) heat in the shallow subsurface is a viable sustainable space heating alternative. In terms of management of the geothermal potential of cities we developed a new classification of existing assessment concepts and suggested a new policy framework for licensing geothermal heat pump systems based on extensive literature reviews. We also developed and validated field and simulation techniques that help to assess the thermal ground properties and interference of nested shallow geothermal systems. The proposed modelling approaches lower the computational demand and require less data compared to conventional models by using backward modelling to map the thermal catchment zone of shallow geothermal units. The developed management concepts and quantification of thermal processes in the shallow subsurface have the potential to boost the awareness and applicability of shallow geothermal heat pump systems especially in urban environments. Hereby they can substantially assist decarbonization of the building sector.

Projektbezogene Publikationen (Auswahl)

 
 

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