Thermal conditions in shallow ground and groundwater

Currently, research on heat transport in the subsurface is in a renaissance. This is stimulated by the observed response of the ground thermal regime to climate change, by the growing interest in geothermal energy use, and by the manifold efforts to integrate natural temperature variation in hydrogeological models. I am interested in thermal energy fluxes in the shallow ground and across the ground surface. This is addressed mainly from a geoscientific perspective, based on a range of laboratory and field measurement campaigns, closely linked to model development. Laboratory work covers standard small-scale measurements of thermal properties, as well as high resolution sensing of voluminous sandbox aquifers. My most popular field labs are cities, with often pronounced thermal alterations of the ground, a phenomenon that is described as subsurface urban heat island (UHI).

Currently, research on heat transport in the subsurface is in a renaissance. This is stimulated by the observed response of the ground thermal regime to climate change, by the growing interest in geothermal energy use, and by the manifold efforts to integrate natural temperature variation in hydrogeological models. I am interested in thermal energy fluxes in the shallow ground and across the ground surface. This is addressed mainly from a geoscientific perspective, based on a range of laboratory and field measurement campaigns, closely linked to model development. Laboratory work covers standard small-scale measurements of thermal properties, as well as high resolution sensing of voluminous sandbox aquifers. My most popular field labs are cities, with often pronounced thermal alterations of the ground, a phenomenon that is described as subsurface urban heat island (UHI).

Are these subsurface UHIs a blessing or a curse? On the one hand, elevated ground temperatures might promote the growth of pathogens in groundwater. On the other hand, the amount of heat available in such aquifers offers a great potential to cover energy demands and/or storages in urban areas, using it for space heating or cooling by means of geothermal heat pump systems. To take advantage of this potential of urban aquifers, the principal heat transport processes in the subsurface urban heat islands have to be comprehensively understood. Hence, the main objective of our research is to examine the intensity of subsurface UHIs and to quantify all dominant heat fluxes beneath. As study sites, we selected several cities, such as Cologne, Karlsruhe and Zurich, to be able to distinguish between site-specific and universally valid findings.

How can we describe more efficiently and precisely the consequence of shallow geothermal energy use on ground and groundwater? I set a main focus on versatile analytical modelling techniques, especially for simulating multiple interacting processes such as advection, diffusion and dispersion. Existing approaches are further developed in order to account for spatially and temporally variable boundary conditions. For model validation, we work with long-term measurements of borehole heat exchangers and groundwater heat pump systems. In our studies, we highlight the role of groundwater flow on geothermal systems, the often underestimated effect of mechanical dispersion on evolving ground thermal anomalies, and the considerable contribution from land surface energy fluxes in shallow geothermics.

We offer a state-of-the-art perspective of this field in our recently published textbook, “Thermal use of groundwater”.

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