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Why do floods, storm surges, and tsunamis often cause high numbers of deaths?

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In the field of disaster epidemiology, floods, storm surges, and tsunamis are identified as the most significant natural disasters in terms of mortality. Unlike other events such as earthquakes or windstorms, which often result in a higher ratio of nonfatal injuries to deaths, water-related disasters frequently exhibit a frequency of mortality that exceeds the frequency of nonfatal injuries.1

Several factors contribute to these high death tolls:

Nature of the Hazard: Water-related events often involve massive physical force and inundation, which can overwhelm local institutions and exceed available response resources.21
Vulnerability and Infrastructure: Mortality is significantly higher in low- and middle-income countries where there is greater vulnerability due to poverty, poor urban planning, and a lack of resources for public health infrastructure.31
Population Density: Events occurring in densely populated areas, particularly on vulnerable ground like undefended coastal plains or river watersheds, result in greater absolute numbers of deaths.1
Secondary Impacts: While the initial event causes the most immediate deaths, the aftermath can lead to further health crises if there is significant population displacement, destruction of shelter, and the disruption of essential health services.1