For decades and centuries, water management primarily meant to master streamflow in the river bed. Hydrological research was part of civil engineering and focused on modeling and validation of discharge. For the analysis and prediction of impacts of global climate- and land use change on a variety of spatial and temporal scales, however, the understanding of the intertwined water- and energy cycle in the climate system requires the compartment crossing description of all water fluxes in the atmosphere, the land surface and the subsurface. This is achieved by Earth System models, and particular coupled regional atmosphere-hydrology model systems. Their validation requires a multitude of hydrological variables that are far beyond discharge. The compartment crossing observation of hydrometeorological variables is achieved e.g. by current measurements campaigns within TERENO-preAlpine (Terrestrial Environmental Observatories) in Germany or by efforts to setup and operate a hydrometeorological observatory in West Africa via WASCAL (West African Science Service Centre for Climate Change and Adapted Land Use). Current approaches for the fully coupled modeling of both the atmosphere and terrestrial compartments of the water cycle with regional model systems will be presented. For different regions worldwide (Germany, West Africa, China), the performance of the fully coupled model systems WRF-Hydro is evaluated. In addition, the role of lateral terrestrial water fluxes and their feedback to the atmosphere is discussed.