What fundamental physical process is seamlessly integrated by a coupled hydrological-hydraulic model that a standalone hydraulic model would typically require as an external input?

The fundamental physical process seamlessly integrated by a coupled hydrological-hydraulic model that a standalone hydraulic model would typically require as an external input is the rainfall-runoff transformation, also known as the generation of surface runoff from precipitation. This process describes how atmospheric precipitation, such as rainfall or snowmelt, interacts with the land surface and subsurface to produce water flow that eventually enters a river or stream system. It involves complex interactions including infiltration, where water soaks into the soil; evaporation, where water returns to the atmosphere; and interception, where vegetation temporarily holds water, ultimately determining the volume and timing of water flowing over the land and into water bodies.