Hydrologic modeling is simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrologic prediction and for understanding hydrologic processes. There are two hydrological models: Stochastic Models and Process-Based Models. Hydrological modelling is a valuable tool for studying the processes governing impacts of climate change and urban development on water resources and for projecting potential ranges of impacts from scenarios of future change. To improve understanding of processes involved and to project potential future conditions, hydrologists rely on models to simulate system behaviour. Hydrological modelling is a useful methodology for experimenting with the dynamics that govern complex environmental and social systems and for projecting possible ranges of impacts. Hydrologic models are simplified, conceptual representations of a part of the hydrologic cycle. Hydrological models can range from sand-filled boxes to complicated computer program. They are primarily used for hydrologic prediction and for understanding hydrologic processes. Recent research in hydrologic modelling tries to have a more global approach to the understanding of the behaviour of hydrologic systems to make better predictions and to face the major challenges in water resources management.