Urban flooding occurs when heavy rainfall, overflowing rivers, coastal water, or overwhelmed drainage systems exceed a city's capacity to absorb and safely move water. Its effects extend beyond the flooded area, disrupting homes, transport, health services, infrastructure, and everyday life.
Roads, roofs, and other hard surfaces prevent rainfall from soaking into the ground. Flood risk increases when intense rain combines with limited drainage, loss of wetlands and open ground, development in flood-prone locations, rising coastal water, or poorly maintained infrastructure.
Floodwater can cause drowning and injury, contaminate water and food supplies, damage homes, interrupt electricity and transport, and restrict access to healthcare. Repeated flooding can also create long-term financial and mental-health pressures. Impacts are often greatest where housing and drainage are inadequate and households have fewer resources to prepare or recover.
Cities can combine flood-risk mapping, rainfall and river monitoring, early warnings, maintained drainage, permeable surfaces, wetlands, rain gardens, and other blue-green infrastructure. New development should avoid the highest-risk locations, while vulnerable neighbourhoods need targeted protection, accessible evacuation plans, resilient public services, and fair recovery support.
