Modern hydrogeology has been built on the idea that the temperature distribution in the upper kilometer of continental landmasses is in quasi-equilibrium and is determined by the long-term ground surface temperature and the heat flux from the Earth’s interior. The presumed thermal stability of groundwater is important for many groundwater and stream ecosystems which cannot tolerate a wide temperature range and face growing threats from climate and land-use changes. Yet, recent results have evidenced the great impact of ongoing atmospheric warming on shallow groundwater temperatures. Groundwater flow is expected to strongly affect groundwater and stream warming trends. A major issue is that existing modeling frameworks have largely sidestepped (1) the complexities associated with multi-scale heterogeneity in groundwater flow, and/or (2) the transient nature of groundwater fluxes and surface temperature. Furthermore, direct field evidences of the impact of climate and anthropogenic forcings on the temperature distribution are rare. The CONCRETER assesses the role of groundwater dynamics in shaping the thermal regime of the critical zone, the shallow subsurface where the water, element, energy and biological cycles interact.
The focus on the interaction of subsurface heterogeneity with heat transport processes requires:
(WP1) The development of original numerical models to explore large-scale thermal behavior in a fractured geological formation.
(WP2) The development of novel experimental methodologies to perform dynamical pore scale optical measurements of temperature.
(WP3) New critical in situ data to directly estimate the distribution of groundwater fluxes and rock thermal and to constrain the models developed within WP1.
(WP4) The further development of advanced numerical models to separate the effects of fluid flow and of surface warming.
(WP5) To measure changes in temperature on well-characterized sites chosen to isolate each effect (natural flow, pumping, surface heating). Complemented by data on the heterogeneity of hydraulic and thermal properties (WP3), we will analyze collected data sets using the newly developed 3D numerical models of flow and heat transport (WP1 and WP4).
Through these steps, CONCRETER will lay new theoretical and practical foundations to understand the interplays between flow and heat transport processes, fully integrating the up-to-now neglected role of the groundwater hydrodynamics and the specific role of flow variability.
