Combining monitoring and modelling tools as a basis for city-scale concepts for a sustainable thermal management of urban groundwater resources.

Increasing anthropogenic impacts lead to elevated temperatures of the shallow subsurface, including the unsaturated and groundwater saturated zone, in many urban areas in comparison to unaffected natural thermal states. The "current thermal state" of four groundwater bodies in the urban area of Basel-City, Switzerland, was investigated by means of high-resolution multilevel temperature wells and numerical 3D groundwater flow and heat transport models. The calibrated and validated numerical groundwater flow and heat transport models allow evaluating and comparing groundwater and heat fluxes for the investigated groundwater bodies and defined cross-sections for differing urban districts, e.g. residential and industrial areas under development. We present the overall and the specific advective heat fluxes within two urban districts, which will be restructured in the near future. The management of groundwater resources in urban areas plays an important role not only for groundwater quantity but also for its quality, i.e. thermal subsurface and groundwater regimes. We demonstrate how monitoring and modelling tools can be the basis for a sustainable management of complex urban groundwater resources. Furthermore, we argue that such tools should be integrated in the thermal management of urban groundwater bodies. Such tools also allow integrating the potentially available energy of shallow subsurface resources into energetic management strategies on the urban scale.