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).

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  • Namibia has received heavy rains over the past three weeks, resulting in floods in the north-eastern and north-western parts of the country. The heavy rains in neighbouring Angola exacerbated the situation, leading to devastating floods in Namibia. The four north-western regions affected by the floods are the Oshana, Ohangwena, Omusati and Oshikoto regions.

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    Source : Charter activation

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  • Heavy rainfall between 19 and 28 of January has caused flooding in southern part of Bosnia and Herzegovina. The vast water masses have severely affected the population in the municipalities of Trebinje, Popovo polje, Ravno, Neum and Svitava.

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  • Heavy rains in Morocco have claimed 24 lives and forced 2,000 people to be evacuated over the past week, interior ministry officials said Saturday.

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    Heavy rains since 2 February have claimed 24 lives and forced 2,000 to be evacuated over the past week. Rivers rose and houses were swept away in landslides, causing over 2,000 homes to be lost.
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