Flood
Definition
Flood is usually used as a general term to describe the overflow of water from a stream channel into normally dry land in the floodplain (riverine flooding), higher-than–normal levels along the coast and in lakes or reservoirs (coastal flooding) as well as ponding of water at or near the point where the rain fell (flash floods) (IRDR Glossary).
Facts and figures
Floods are the natural hazard with the highest frequency and the widest geographical distribution worldwide. According to the Organization for Economic Cooperation and Development (OECD) flooding is one of the most common, widespread and destructive natural perils, affecting approximately 250 million people worldwide and causing more than $40 billion in damage and losses on an annual basis (OECD).
Flooding occurs most commonly from heavy rainfall when natural watercourses lack the capacity to convey excess water. It can also result from other phenomena, particularly in coastal areas, by a storm surge associated with a tropical cyclone, a tsunami or a high tide. Dam failure, triggered by an earthquake, for instance, will lead to flooding of the downstream area, even in dry weather conditions.
Various climatic and non-climatic processes can result in different types of floods: riverine floods, flash floods, urban floods, glacial lake outburst floods and coastal floods.
Flood magnitude depends on precipitation intensity, volume, timing and phase, from the antecedent conditions of rivers and the drainage basins (frozen or not or saturated soil moisture or unsaturated) and status. Climatological parameters that are likely to be affected by climate change are precipitation, windstorms, storm surges and sea-level rise (UNDRR).
When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials such as sharp debris, pesticides, fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera (UNDRR).
Further information
UN-SPIDER Regional Support Offices with hazard-specific expertise
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Data Source
Event
The Asia and Oceania regions are frequently affected by severe natural phenomena such as tropical cyclones, torrential monsoons, volcanic eruptions, yellow sandstorms, floods, sea ice, and wildfires. The importance of monitoring the climate and the environment is also increasing, which has prompted enhanced global interest in the field.
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News
The government of Niger, in partnership with the World Bank and a team of local volunteers, steps up the gathering of data on Niamey’s exposure to floods using drone and open source data to support disaster preparedness.
The initiative started with a team of volunteers, students and young professionals who used an open source mobile application to build a database on exposed people and assets in Niamey, the capital city.
The team has so far gathered about 15,000 data point on household and infrastructure in the region. Drone African Service, a Nigerien startup has been providing training on the use of drones to acquire high-resolution images of exposed people and facilities. This is further analyzed and modelled for flood risk of the most vulnerable communities, which will be further shared with Nigerien government authorities on the risk data portal.
Drone Africa Services trained the team on digital cartography using OpenStreetMaps and a mobile application... read more
GP-STAR factsheet
The identification of critical glacial lakes is based on remote sensing method in which several criteria related to glacial lakes, glaciers and physical condition of surrounding area is considered to assess potential for future outburst and possible glacial lake outburst flood (GLOF).
