The ICON-ParFlow coupling: Integrating a continental-scale hydrological model into an Earth system model

3D prognostic groundwater flow on a global scale is currently lacking in Earth system models. In order to prepare Earth system models for kilometer-scale simulations with integrated continental hydrology, the ParFlow hydrological model has been coupled to the land model of the ICON modelling framework. Global simulations of atmosphere and land were conducted with a two-way coupling between ParFlow and the soil hydrological scheme of ICON-Land over the Pan-European region. In this first configuration, ParFlow and ICON-Land exchange surface moisture fluxes and liquid soil water. Analyzing simulations covering the extended summer months, it is found that the coupling with ParFlow significantly reduces the soil-water variability in the deeper soil layers by resolving actual shallow aquifers. In ParFlow, surface runoff and infiltration are more physical resulting in a more realistic response of soil moisture to weather patterns on longer time scales. Correlations of soil moisture with surface latent heat flux and atmospheric moisture transport show that this results regionally in an increased land-atmosphere coupling strength. Also, the lateral flow of near-surface groundwater, which is intrinsically linked to the formation of river networks, influences atmospheric variables related to cloud formation by increasing their horizontal heterogeneity. Apart from these results, which demonstrated the importance of an integrated hydrological model for shallow groundwater in Earth system modelling, first results of high-resolution coupled simulations with an extended ParFlow coverage on a latitude belt over the tropical zone at 1 km resolution are presented.