Flood forecasting

Flood forecasting predicts the timing, location, extent, or severity of future floods using observations, hydrological models, and weather information.

Numerical weather prediction: Computer-based simulation of the atmosphere used to predict future weather conditions. Forecast rainfall provides a key upstream input to many flood predictions.
Flood warning: An official alert that flooding is occurring or expected and that protective action may be needed. Forecasts provide advance notice for issuing warnings before flood impacts arrive.
Watershed: An area of land that drains precipitation and surface water to a common outlet. Its shape, soils, and drainage define the area whose response the forecast must represent.
Flood nowcasting: The very short-range prediction of imminent flooding using current observations and rapidly updated information. Nowcasting emphasizes immediate conditions, while broader flood forecasting can target longer lead times.
Forecast uncertainty: The range of plausible outcomes arising from imperfect observations, models, and knowledge of a system. Uncertainty in rainfall and runoff limits confidence in predicted flood timing and magnitude.
Hydrological model: A mathematical representation of how water moves through a landscape and its rivers. These models translate precipitation and land conditions into runoff and river flow.
Flood risk management: The policies and actions used to reduce harm from floods and manage their consequences. Forecasting is an operational tool within broader efforts to limit flood losses.
Streamflow: The volume of water flowing through a river channel per unit of time. Predicted discharge is a central quantity used to assess whether rivers may flood.
River flood forecasting: The prediction of future river levels or flows that may exceed flood thresholds. It focuses on river behavior, unlike flood forecasting that may also address other flood sources.
Data assimilation: The process of combining observations with a model to estimate a system's current state. Better integration of river and weather observations can improve the starting state of forecasts.

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