Surface Water Flooding
Primary reference(s)
WMO, 2012. Definition number 1465. International Glossary of Hydrology. WMO-No. 385. World Meteorological Organization (WMO). Accessed 17 April 2020.
Additional scientific description
Surface water flooding is caused when the volume of rainwater falling does not drain away through the existing drainage systems or soak into the ground but lies on or flows over the ground instead. This type of flooding is usually short-lived and associated with heavy downpours of rain, thunderstorms etc. (NFU, 2019). The UK Government provides a real time flood information service which is easily accessible (UK Government, no date).
Metrics and numeric limits
Not identified.
Key relevant UN convention / multilateral treaty
Not identified.
Examples of drivers, outcomes and risk management
Floods tend to be caused by a number of natural events such as rain from slow moving or stationary low-pressure areas, thunderstorms, and tropical cyclones. The amount and duration of the rainfall, soil type and saturation, geography and whether it is an urban area can affect the magnitude and impacts of the flooding. Flooding can occur at the place of a heavy rain event or far downstream away from the causal rain event. Flooding can also be caused by other factors such as storm surge, tsunamis, ice jam, glacial lake outburst, as well as being human influenced such as dam burst, improper land use planning, etc. (Geoscience Australia, no date).
Floods are one of the most common hazards. The effects of flooding on health are extensive and significant, ranging from mortality and injuries resulting from trauma and drowning to infectious diseases and mental health problems (acute and longterm). While some of these outcomes are relatively easy to track, ascertaining the human impact of floods is still weak. For example, it has been reported that two-thirds of deaths associated with flooding are from drowning, with the other third from physical trauma, heart attacks, electrocution, carbon monoxide poisoning and fire. Often, only immediate traumatic deaths from flooding are recorded (WHO, 2013).
Morbidity associated with floods is usually due to injuries, infections, chemical hazards and mental health effects (acute as well as delayed) (WHO, 2013). Hypothermia may also be a problem, particularly in children, if trapped in floodwaters for lengthy periods (WHO, no date). There may also be an increased risk of respiratory tract infections due to exposure (loss of shelter, exposure to flood waters and rain). Power cuts related to floods may disrupt water treatment and supply plants thereby increasing the risk of water-borne diseases as well as affecting proper functioning of health facilities, including cold chain (WHO, no date). Floods can potentially increase the transmission of the following communicable diseases: water-borne diseases (such as typhoid fever, cholera, leptospirosis and hepatitis A) and vector-borne diseases (such as malaria, dengue and dengue haemorrhagic fever, yellow fever, and West Nile Fever) (WHO, no date).
The longer-term health effects associated with a flood are less easily identified. They include effects due to displacement, destruction of homes, delayed recovery and water shortages (WHO, 2013).
References
Geoscience Australia, no date. Flood. Accessed 23 March 2021.
NFU, 2019. Environment Agency (EA) maps show risk from surface water flooding. National Farmers Union (NFU). Accessed 2 October 2020.
UK Government, no date. Flood information service. Accessed 2 October 2020.
WHO, no date. Flooding and communicable diseases fact sheet. World Health Organization (WHO). Accessed 4 October 2020.
WHO, 2013. Floods in the WHO European Region: Health effects and their prevention. World Health Organization (WHO), Regional Office for Europe. Accessed 2 October 2020.