Hydrology is the study of the distribution and movement of water on and below the Earth's surface, as well as the impact of human activity on water availability. Various hydrological models have been developed worldwide to understand the impact of climate and soil on water resources, with the best models providing results close to reality using few parameters. Rainfall-runoff models are classified as lumped or distributed based on how model parameters vary over space and time, and as deterministic or stochastic based on other criteria. Examples of hydrological models discussed include SWAT, MIKE SHE, HBV, TOPMODEL, and VIC.