Groundwater flow CONtrols on CRitical zonE ThErmal Regime

ongoing

The foundations of modern hydrogeology have been built within the paradigm of quasi-equilibrium temperature distribution within groundwater systems. The presumed thermal stability of groundwater is vitally 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 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 the 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 still rare. The CONCRETER will therefore assess 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 will require the development of original numerical models (WP1) and novel temperature imaging laboratory experiments (WP2). WP3 will bring critical in situ data to constrain these newly developed models. WP4 will further develop advanced numerical models to separate the effects of fluid flow and of surface warming. With the help of the developed numerical approaches, WP5 will study the evolution of temperature at field sites (characterized in WP3) chosen to isolate the role of different forcings (climatic, anthropogenic) on critical zone thermal regime. CONCRETER will provide new physical frameworks and modelling tools for multi-scale heat transport processes in the critical zone, with the potential to re-define their quantitative understanding.