Floods

Floods are the temporary inundation of land by water from rivers, rainfall, coastal storms, or dam and infrastructure failures. They occur when water exceeds the capacity of channels and drainage systems to carry it away, or when barriers are breached.

Causes include prolonged heavy rainfall, rapid snowmelt, storm surges, dam or levee failures, and urbanization that increases surface runoff. Climate variability and extreme weather events have increased the frequency and intensity of some floods.

Common types include river floods, which arise when rivers overflow; coastal floods, driven by storm surge and high tides; urban floods, from overwhelmed drainage in densely built areas; and flash floods, rapid floods in small basins after intense rainfall.

Flooding can endanger life, damage homes and infrastructure, contaminate water supplies, and disrupt transportation, energy, and healthcare services. Economic losses can be substantial, and floods often lead to displacement, disease outbreaks, and long-term environmental changes.

Forecasting combines rainfall predictions, river gauges, satellite data, and hydrological models to issue warnings. Early warnings, evacuation plans, and community preparedness significantly reduce casualties and damage.

Mitigation measures include river management, levees and dams, retention basins, floodplain zoning, and land-use planning to reduce runoff. Structural and non-structural strategies, including insurance, building codes, and public education, enhance resilience.

Flood risk varies by region depending on climate, topography, land use, and infrastructure. Global data show floods are among the most frequent and costly natural hazards, affecting millions of people annually.