HMS, a physically-based parameter-distributed model system, is comprised of four component models or modules: Soil Hydrologic Model (SHM), Terrestrial Hydrologic Model (THM), Ground-Water Hydrologic Model (GHM), and Channel Ground-Water Interaction (CGI). HMS was developed by Zhongbo Yu to model hydrologic processes, such as vertical soil-moisture flow, evapotranspiration, infiltration, overland flow, channel flow, and ground-water flow, within a river basin, and to simulate the river-basin response to climatic and atmospheric forcings. HMS fully utilizes digital and remotely sensed data sets (e.g., elevation, soil, vegetation, precipitation).