HYSIM is a hydrological simulation model (rainfall runoff model), which uses rainfall and potential evaporation data to simulate the hydrological cycle (surface runoff, infiltration into groundwater and river flows). HYSIM can use data from rainfall, potential evaporation (PET), snow melting and extraction from groundwater and surface water. Only data on rainfall and potential evaporation are essential. The simulation time can be a day or less. Typical uses of HYSIM include: