Some 1.5 billion people were affected by floods in the last decade of the 20th century. Floods threaten human life and property worldwide. Dam breaks or sudden regulatory operations such as the release of water for hydro-electric power generation can also cause catastrophic flooding. Dikes or flood levees can overtop causing floods when the rivers carry large amounts of snowmelt. In coastal areas, storm surge caused by tropical cyclones, tsunamis, or rivers swollen by exceptionally high tides can cause flooding. They can be triggered by severe thunderstorms, tropical cyclones, large low pressure systems, monsoons, ice jams or melting snow. Floods come in a number of forms, from small flash floods to sheets of water covering extensive areas of land. Flash floods can also occur after a period of dry conditions when moderate or heavy rain falls onto very dry, hard ground that the water cannot penetrate. All floodplains are vulnerable and heavy rain or thunderstorms can cause flash flooding in any part of the world. Some National Meteorological and Hydrological Services and specialized centres have responsibility for investigating geophysical hazards including volcanic explosions (airborne ash) and tsunamis, and hazardous airborne matter (radionuclides, biological and chemical substances) and acute urban pollution.įloods can occur anywhere after heavy rain events. Winter storms with high winds and heavy snow or freezing rain can also contribute to avalanches on some mountain slopes and to high runoff or flooding later on in the melt season. In temperate latitudes, severe thunderstorms can be accompanied by a combination of large, damaging hail stones, tornadoes, strong winds or heavy rain resulting in flash floods. In addition to high winds and heavy rain, a tropical storm can result in flooding and mudslides. An extreme weather event can involve multiple hazards at the same time or in quick succession. Others, such as droughts, develop slowly, but can affect most of a continent and entire countries for months or even years.
Tornadoes and flash floods are short-lived, violent events, affecting a relatively small area. Natural hazards occur across different time and area scales and each is in some way unique.
WMO coordinates the efforts of National Meteorological and Hydrological Services to mitigate human and property losses through improved forecast services and early warnings, as well as risk assessments, and to raise public awareness. WMO Disaster Risk Reduction activities are integrated and coordinated with other international, regional and national organizations. To support the assessment of global progress in achieving the outcomes and goals of the Sendai Framework, seven global targets have been agreed, most of which have direct implications for WMO and its Members.
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By issuing accurate forecasts and warnings in a form that is readily understood and by educating people on how to prepare against such hazards, before they become disasters, lives and property can be protected. Emphasis is on disaster risk reduction: one dollar invested in disaster preparedness can prevent seven dollars’ worth of disaster-related economic losses – a considerable return on investment.Īs signatories to the Sendai Framework for Disaster Risk Reduction 2015–2030, WMO Members have undertaken to prevent new and reduce existing disaster risk through the implementation of a range of integrated and inclusive measures that prevent and reduce hazard exposure and vulnerability to disaster, increase preparedness for response and recovery and thus strengthen resilience. Human and material losses caused by such disasters are a major obstacle to sustainable development. UNISDR: Global Assessment Report on Disaster Risk Reduction 2015 However, in relation to annual capital investment or social expenditure, many low and middle-income countries, and in particular small island developing states (SIDS), have the highest concentrations of risk. This risk presents a real challenge to the global agenda of sustainable development. (.) In absolute terms, global average annual loss is concentrated in large, higher-income, hazard-exposed economies. The global expected average annual loss in the built environment associated with tropical cyclones (wind and storm surge), earthquakes, tsunamis and floods is now estimated at US$314 billion.
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