"Land surface processes play a key role in Earth climate. As a core component of state-of-the-art Earth System Models (ESMs), the representation of these processes influence future climate change projection as investigated in international multi-model initiatives such as CMIP6 & CMIP7. Hydrological processes and trends coupled with climate change are often retained to provide positive feedback able to exacerbate future climate transitions. However, land hydrology and its numerous interactions with other components of the Earth system (biosphere, biogeochemical cycles, anthropogenic disturbances/practices) is crudely represented in most state-of-the-art ESMs inducing erroneous response to anthropogenic climate forcers at both global and regional scales. For instance, anthropogenic and climate-induced continuous decline of groundwater levels has already started in several arid and semi-arid areas, threatening the subsistence of groundwater-dependent ecosystems that may be no longer guaranteed and so with the risk of ecosystem shifts and/or progressive levels of desertification. Recent progress in our understanding of prominent land surface processes call for a community discussion on how the representation of the hydrological, biophysical and biogeochemical processes are operated in land surface models. Such discussion is motivated by arising policy-relevant questions related to the representation of the interaction between hydrological processes and biosphere (including the human component) to properly investigate the carbon-water nexus as well as the effects of land-based mitigation/adaptation options (e.g. involving management of forests, crops and irrigation practices, etc). In the framework of ongoing EU projects (e.g. OptimESM, https://optimesm-he.eu/; RESCUE, www.rescue-climate.eu; ESM2025, www.esm2025.eu) some tentative efforts in this direction have recently started.
This Town Hall meeting will try to further overcome any silo approach by initiating an interdisciplinary exchange of ideas from members of the involved international modeling communities to identify and formulate future needs, strategies and opportunities for the next generation of ESMs. Best practices in coordination will be discussed that could facilitate the involvement of hydrologists and climate scientists together in interdisciplinary scientific teams. Further, any possibility to develop cross-cutting activities and/or to propose joint panels in the framework of international research programmes will be investigated. Particular focus will be on the identification and discussion of possible future funding opportunities for the envisaged interdisciplinary modeling initiatives for the next generation of land surface models."