Integrating the ParFlow hydrological model into ICON

In order to further develop an ICON-based, storm-resolving earth-system model, the ParFlow hydrological model has been coupled to the ICON land component, which is based on the JSBACH land surface model. The overall goal is to better capture land-atmosphere interactions ensuring balanced water and energy budgets in global, kilometer-scale simulations on the climate time scale. Compared to the JSBACH hydrology, ParFlow allows a variable subsurface thickness and 3D groundwater dynamics in connection with resolved overland flow in a continuum approach. In combination with the two-way feedback between atmospheric and hydrological processes provided by the coupling, this is expected to resolve hydrological processes more realistically in space and time. Technically, the YAC coupling library has been used to account for horizontal grid differences and different spatial and temporal resolutions in ICON and ParFlow.
In the proposed global setup, ParFlow has been implemented over a European domain with a subsurface depth of 60 m to account for deeper aquifers. Thus, 3D groundwater dynamics and two-way-coupling with the land surface and atmosphere is active only over that specific region of interest while the rest of the global land surface relies on the default hydrological model of JSBACH. This way, no atmospheric boundary data needs to be provided in contrast to regional weather and climate model setups so that a closed representation of the global water cycle can be established including regional feedbacks with groundwater. In addition to a general proof-of-concept, our presentation provides a first analysis of moisture distribution and land-atmosphere fluxes both inside and outside the coupling region as well as potential feedbacks of groundwater on the atmospheric circulation and large-scale weather patterns beyond the regional scale.