The area of land where all precipitation collects and drains into a common outlet, such as a river, lake, or ocean. Also known as a watershed or drainage basin.
A catchment, also called a watershed or drainage basin, is the geographical area bounded by topographic divides within which all surface water and shallow groundwater flow converge to a single outlet point. Catchments range in scale from small headwater areas of a few hectares to major continental river basins spanning millions of square kilometers. The physical characteristics of a catchment, including its area, shape, slope, soil type, land cover, and drainage density, fundamentally control the hydrological response to precipitation. Catchment delineation is typically performed using digital elevation models (DEMs) and geographic information systems (GIS). Understanding catchment hydrology is essential for flood prediction, water resource assessment, pollution management, and ecological conservation. Land use changes within a catchment, such as urbanization or deforestation, can significantly alter runoff patterns, water quality, and downstream flood risk. Modern integrated water resource management (IWRM) uses the catchment as the fundamental planning unit.