Past, present and future of subsurface urban heat islands in China and Germany - implications for geothermal development

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Cities have their roots in the ground. Here are the basements of buildings, essential infrastructure, vital freshwater and renewable energy resources. Here, soil and groundwater temperatures appear substantially increased when compared to ambient undisturbed conditions, i.e. the so-called subsurface urban heat islands (SUHIs). Better understanding of the mechanisms forming SUHIs and of the differences between those in different regions will be crucial for developing recipes for proactive urban ground management in the future. The focus of this project is, for the first time, on the comparison of SUHIs in two Chinese and German cities, Nanjing and Cologne. Both research groups have substantial experience in SUHI research in their countries, and they have precious databases from past measurements of soil and groundwater temperature. The purpose is to complement these with a new collaborative measurement program, and to learn from past and present SUHI characteristics about the so far unknown long-term dynamics. By field and laboratory-based experimental work and numerical simulation of ground temperature evolution with transient land use development, the future evolution of SUHIs will be revealed. By comparing the conditions first in German and Chinese cities, and then in selected further cities worldwide, the driving factors in different urban environments will be identified. Ultimately, more reliable predictions of the future subsurface development also in other cities without detailed site investigation is facilitated.