Hydrological models (precipitation-runoff-models) deal with the relationship of water in the environment, investigating the occurrence, circulation and distribution of water within each phase of hydrologic cycle. Moreover, these models consider the chemical and physical properties and the interaction with the environment. Due to land cover changes, increasing urbanization, industrialization and deforestation various changes have been occurred in hydrologic systems around the world. Climate change as well as soil heterogeneity also have a direct impact on the discharges of many rivers. Today there is a big variety of different hydrological models available to analyze these relations. These models are used for the modelling of both gauged and ungauged catchments. Each model has its own unique characteristics. The inputs used by different models are rainfall, air temperature, soil characteristics, topography, vegetation, hydrogeology and other physical parameters. All these models can be applied in very complex and large basins. The results help to manage flood forecasting, proper water resource distribution, evaluation of water quality, erosion, sedimentation, land use changes, nutrient and pesticide circulation as well as the impact of climate change scenarios. (Gayathri et al. 2015)

Some hydrological models also include or can be connected to groundwater models in order to get a more holistic picture of the hydrologic system in a specific catchment.