Flooding affects many regions across the world and can occur in any area, yet some areas are more exposed to floods and ensuing health consequences than others.

Areas of the world particularly impacted by flooding events – due to high vulnerability, high exposure, or both – include:

• Small Island Developing States (SIDS)
• Densely populated areas with low capacity to cope with the impacts of flooding
• Areas where expansion of population and property in flood plains has occurred
• Low-lying coastal regions
  Urban areas

Drowning accounts for 75% of deaths in flood disasters. Deaths also result from physical trauma, heart attacks, electrocution, carbon monoxide poisoning and fire associated with flooding. Often, only immediate traumatic deaths from flooding are recorded. ^{10 10}WHO: FloodsX

Floods can also have medium- and long-term health impacts, including: ^{11 11}WHO: FloodsX

• water- and vector-borne diseases, such as cholera, typhoid or malaria
• injuries, such as lacerations or punctures from evacuations and disaster cleanup
• chemical hazards
• mental health effects associated with emergency situations
• disrupted health systems, facilities and services, leaving communities without access to health care
• damaged basic infrastructure, such as food and water supplies, and safe shelter.

Injury

Flash floods that occur very quickly are more likely to cause immediate injury.

Water-borne Disease

Rises in water level can impact sewage systems, and when flooding causes sewage and drinking water to mix it can result in water-borne pathogens entering the water supply.

Storm surges and sea level rise can cause the contamination of groundwater through saltwater intrusion and compromising sanitation and hygiene, resulting in outbreaks of water-borne diseases, hypertension and eclampsia.

Vector-borne Disease

Stagnant pools of water provide ideal conditions for bacterial growth and create breeding grounds for disease-carrying vectors such as mosquitoes.

Food Security and Nutrition

Saltwater intrusion on agricultural land and resultant crop and livestock loss can diminish food security and cause nutrient deficiencies and malnutrition. Also, pollutants spread by flood waters might contaminate agricultural soils and introduce harmful elements in the food chain.

Flood-associated drowning risks are higher in low- and middle-income countries where people live in flood prone areas and where the government’s ability to warn, evacuate, or protect communities from floods is weak or only just developing. ^{12 12}WHO: FloodsX   Those in high income countries are also at risk where urbanization plans fail to take into account flood risk or to coordinate emergency response.

Between 1994 and 2013 Asia and Africa experienced more floods than other continent, ^{13 13}The Human cost of Natural Disasters: A global perspective. CRED, 2015.X and the size of populations living in flood prone areas have increased by 114% and 192%, respectively.^{14 14}Global Assessment Report on Disaster Risk Reduction 2011. UNISDR, 2011X

Children, the elderly and those with limited mobility are at a greater risk of mortality from floods.^{15 15}The human impact of floods: a historical review of events 1980-2009 and systematic literature review. Doocy et al. 2013X Displaced populations without access to adequate health care and clean drinking water are also at elevated risk, as are people in poor farming communities in flood prone areas.

In developed countries, males are more likely to die during floods, while in less developed countries women have a higher mortality risk.^{16 16}The human impact of floods: a historical review of events 1980-2009 and systematic literature review. Doocy et al. 2013X

Floods are made more likely by the more extreme weather patterns caused by long-term global climate change. An increase in global temperatures leads to both higher snowmelt rates and an increase in precipitation intensity, duration and/or frequency – the major triggers for flood events.

As climate change increases the likelihood for more extreme weather events to occur, risks will expand beyond the high-risk areas known today. More extreme flooding must be expected, and for the towns and cities where flooding has already occured, theirs will no longer be only a ‘once in a lifetime’ risk.^{17 17}UNEP: How climate change is making record-breaking floods the new normal: A series of recent stormsX

Floods are also highly influenced by land use and other issues, such as vegetation, that impact the retention capacity of the basin. Environmental change and degradation due to both climate change and human activities (especially deforestation to increase agricultural land) can negatively impact vegetation and retention capacity, and result in heightened flood risk.

The magnitude of the physical and human costs from flood-related disasters can be reduced if adequate emergency prevention, preparedness, response and recovery measures are implemented in a sustainable and timely manner, adopting integrated flood management approaches. ^{18 18}WHO: FloodsX

The health impacts of floods can be reduced by increasing awareness, prevention, preparedness and resilience to flood events. This can be achieved through actions to:

• Understand WHEN a flood might happen: End-to-end early warning systems for flood forecasting, including monitoring of rainfall, snowmelt and discharge as well as forecasting modelling, to produce clear flood alerts and warnings to potentially affected communities.
• Understand WHERE a flood might happen: mapping of flood hazard extent, vulnerability and risk in flooding zones.^{19 19}Global Flood Risk under Climate Change. Hirabayashi et al. 2013. X
• Increase the basin water retention capacity and slow runoff: promote environmental buffering and green infrastructure, such as surface vegetation and green roofs, combined with land-use planning.^{20 20}see APFM: Conservation and Restoration of Rivers and Floodplains and The Role of Land-Use Planning in Flood Management, WMO 2016.X
• River and basin management, including the construction of levee systems and dams to withhold water where needed.^{21 21}see APFM: Reservoir Operations and Managed Flows and APFM: Formulating a Basin Flood Management PlanX
• Design and implementation of evacuation procedures that decrease the risk of individual deaths and immediate injury, including mobile treatment and healthcare centres that can be rapidly set up to deal with waterborne disease outbreaks such as cholera.^{22 22}see APFM: Flood Proofing, APFM: Flood Emergency Planning, and APFM: Health and Sanitation Aspects of Flood ManagementX
• Increase public awareness about flood risk and promote community based flood management.^{23 23}see APFM’s Crisis Mapping and Crowdsourcing in Flood Management, Public Perception of Flood Risk and Social Impact Assessment, The Role of the Media in Flood Management and Community-Based Flood ManagementX