Climate Change and Public Health Factsheets

Climate change, floods and your health

Floods are a common natural hazard in Canada and most floods are due to heavy or prolonged rainfall or snowmelt.

What causes flooding?

  • Heavy or prolonged rainfall, or severe storms (e.g. hurricanes or thunderstorms)
  • Rapid snowmelt and environmental factors such as drainage, soil type, and flood control systems
  • Ice jams in rivers
  • Sea level rise and storm surges

Changing rainfall patterns, more extreme storms, rapid snow melt and rising sea levels due to climate change can increase the risk of flooding across Canada. In Canada it is expected, with climate change, that:

  • Most regions in Canada will experience higher than average rainfall, except for southwestern Canada which may see a decreasing rainfall trend in the summer.
  • Most regions in Canada will experience higher extreme rainfall. The east and west coasts will see the smallest increase in maximum rainfall level, however they will have an increased risk of flooding from storm surges and heavy precipitation associated with hurricanes.
  • Sea level will continue to rise and the severity of coastal storms will increase.
  • Northern regions will see a decrease in winter snow and earlier snow melt due to longer summers.

Floods and your health

Although a flood's severity is often measured by lives lost and property damaged, other health impacts are also important.

Immediate and short-term dangers


  • Most deaths from flash floods are people who drown while trying to swim away or while trapped in flooded buildings.
  • Many people drown when driving through floodwater, misjudging how deep the water is and how quickly the current is moving. For example, over 57% of deaths from floods in the United States are associated with motor vehicles.


  • Injuries happen during and after floods when people return to clean and repair their homes.
  • During floods, heavy objects move quickly through floodwater and can hit people.
  • Flooded buildings can have damaged wiring and electrical appliances that could electrocute people or cause fires.
  • In any season most floodwater is well below normal human body temperature and can cause hypothermia.

Related and longer-term dangers

Diseases spread through water contamination and sewage backup

  • Heavy rain can overwhelm drainage, water treatment and sewage systems and contaminate drinking water.
  • Floodwater can mix with pollutants such as agricultural waste, chemicals, raw sewage or metal and can contaminate local waterways that supply drinking water.
  • Combined sewer systems (those that carry both raw sewage and storm water) can overflow and contaminate waterways. Combined sewer systems can also back up into household plumbing and increase the risk of contaminating food and water.
  • Flood-contaminated water can carry diseases that can impact human health.

Diseases spread through food contamination

  • Food contamination and related illness can occur following flooding and power outages given that temperatures required to keep food safe may not have been maintained or that food may have come in contact with contaminated water.

Diseases spread by insects

  • Flooding can increase the abundance of mosquitoes by increasing the still-water habitat in which they breed. This can result in outbreaks of diseases the mosquitoes transmit, such as West Nile virus. More information on how to protect yourself from these diseases can be found at: West Nile virus - Protect Yourself!

Indoor air quality

  • Flooded buildings can stay damp even after floodwater has receded, which can create a perfect environment for bacteria and mold growth that can lead to dangerously poor indoor air quality.
  • Breathing spores from mold and fungi can cause allergic reactions and breathing problems such as coughing, wheezing, and asthma attacks. Mold is a major health problem caused by floods.

Carbon monoxide poisoning

  • Floods often cause power outages.
  • During a power outage, indoor ventilation systems that ventilate gas-powered appliances (such as electrical generators, pressure washers, and cooking tanks), will not work and can cause carbon monoxide poisoning.

Mental health

  • Floods can lead to physical health problems, personal loss and financial difficulties which can result in common mental health disorders such as anxiety, depression.
  • Long term health issues, such as depression and post-traumatic stress disorder, can affect people for a long time after a flood. For example, after Hurricane Katrina most adults with post-traumatic stress disorder still had not recovered two years after the event.

What you can do

Protect yourself from drowning

  • Do not try to drive or wade through floodwater even if it seems shallow.
  • Try to move towards higher ground as soon as you can.
  • Do not wait to evacuate.

Prevent Injuries

  • Stay out of floodwater as much as you can, especially near electric lines or outlets.
  • Avoid electrical shock. Wear rubber boots. Keep extension cords out of the water.
  • Shut the power off to the flooded area at the breaker box. Ask your electrical utility for help if needed.
  • Do not return home after a flood until local authorities have told you it is safe.

Avoid illnesses from food contamination:

  • Throw away perishable foods (including meat, poultry, fish, eggs and leftovers) in your refrigerator when the power has been off for 4 hours or more.
  • Thawed food that contains ice crystals can be refrozen or cooked. Full freezers, if left unopened will keep food frozen for 48 hours (24 hours if half full).
  • Throw away food that may have come in contact with flood or storm water or if the food has an unusual odor, color or texture. Keep in mind that food contaminated with bacteria does not necessarily smell bad or appear spoiled.
  • Be prepared by having a cooler with ice ready to keep refrigerated food cold. Have items on hand that don't require refrigeration and can be eaten cold or heated on an outdoor grill. Shelf-stable food, boxed or canned milk, water and canned goods should be part of a planned emergency food supply. Make sure you have ready to use baby formula for infants and pet food, if needed.

Avoid diseases spread through water contamination and sewage backup

  • Boil your water for 1 minute before drinking it if your local public health unit has issued boil water advisory.
  • Store bottled water at home for emergencies.
  • Avoid drinking dirty or foul smelling water even if there is no boil water advisory.
  • Install backwater valves to prevent sewage backups if your city has a combined sewer system.

Protect against diseases spread by insects

  • Clear out stagnant puddles of floodwater in and around your home.
  • Prevent mosquito bites by using insect repellent and wear protective clothing such as long sleeved shirts, long pants and a hat.

Reduce mold

  • Remove damp items.
  • Use dehumidifiers to dry damp areas if the dampness is not severe.
  • Use professional help to clean and remove mold.
  • Wear protective masks while cleaning areas with mold.

Prevent carbon monoxide poisoning

  • Install at least one carbon monoxide detector in your home, especially if you have indoor gas-powered appliances.

Pay attention to your mental health

  • Learn how to recognize post-traumatic stress disorder, what you can do about it, and where to seek help.

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