rainfallrunoff

Rainfall-runoff is a hydrological process by which precipitation that reaches the land surface is converted into overland flow, interflow, and streamflow within a drainage basin. It represents the change from rainfall inputs to runoff outputs, after accounting for losses such as interception, evaporation, and infiltration.

The amount and timing of runoff depend on antecedent moisture, rainfall intensity and duration, soil properties, land cover, and topography. Runoff generation can occur by infiltration-excess (where rainfall rate exceeds infiltration capacity leading to overland flow) or saturation-excess (where the soil becomes saturated and provides lateral flow). Infiltration and interception reduce drainage entry; groundwater processes and subsurface flow contribute to baseflow. Runoff is routed through channels, producing a hydrograph with a quick, flashy response or a slower, delayed response depending on catchment characteristics.

Modeling rainfall-runoff typically uses rainfall-runoff models. Conceptual models relate rainfall to runoff through reservoir-like storage parameters. Physically based models simulate infiltration and flow in soils using Richards equation and related formulations. Data-driven approaches employ statistical or machine learning methods. Models require rainfall and streamflow data, and may include snow cover and evapotranspiration components in semiarid or temperate climates.

Applications include flood forecasting, watershed management, hydrological design, and water resources planning. Uncertainty arises from data quality, model structure, scale, and non-stationarity due to climate change.