Predicting and Alerting Coastal Flooding

Coastal Flooding Prediction and Alerting Program

The coastal flooding prediction and alerting program allows our meteorologists to issue coastal flooding alerts and forecasts across most of the country, using both the probability and expected impact of an event. These services give early warning to emergency management organizations and Canadians about the risk of coastal flooding. As with other Environment and Climate Change Canada (ECCC) weather warnings, coastal flooding alerts are also colour coded.  The alert colours move from yellow, to orange, to red, as the potential risk increases.

We currently have the capacity to predict and alert for coastal flooding in the following areas: 

• Canada’s Pacific coast
• Canada’s Arctic coast
• Canada's Atlantic coast
• the Great Lakes, and
• the St. Lawrence

While we have the ability to predict and alert for coastal flooding in Ontario, residents of Ontario will continue to receive coastal flooding alerts from provincial authorities.

Coastal Flooding Terminology by Province and Territory

As of 2024, the term “coastal flooding” has replaced the term “storm surge” as the default terminology when issuing alerts. This term more accurately describes the event and its potential impact on Canadians.

However, in some regions we still use the term “storm surge” based on the preferences of provincial or territorial authorities.

Provinces where the term “Coastal Flooding” is used:

• British Columbia
• Manitoba
• Newfoundland and Labrador
• New Brunswick
• Nova Scotia
• Ontario*
• Prince Edward Island

Provinces or territories where the term “Storm Surge” is used:

• Quebec
• Nunavut
• The Northwest Territories
• The Yukon

*In Ontario, provincial authorities will issue flooding alerts. 

Forecasting and Communicating Coastal Flooding Risk

Our meteorologists issue coastal flooding forecasts in all coverage zones using modelling techniques and the Coastal Flood Risk Index. The Coastal Flood Risk Index evaluates the likelihood and expected impact of an event to determine the level of risk it poses. Using this system, meteorologists assign an event a risk rating ranging from low to extreme.

To communicate the risk of coastal flooding, our meteorologists issue forecasts using Coastal Flooding Risk Outlook maps. This information notifies Canadians early of high-impact coastal flooding events and enables informed decision-making out to 5 days.

These maps also inform public authorities and emergency management organizations of the potential risk for coastal flooding events. Receiving this information early helps them plan and respond to high-impact events.

Canadians may see these maps in the media. Coastal Flooding Risk Outlooks are available in graphical format. Technical documentation is also available. Coastal flooding risk index is available in GeoJSON format data.

MSC testing data repository DD-Alpha data can be automatically retrieved with the Advanced Message Queuing Protocol (AMQP) as soon as they become available through the Coastal Flooding Risk Index. Technical documentation on predicting and alerting for coastal flooding is also available. 

What is Coastal Flooding

Coastal flooding is a regular occurrence along Canada’s coasts, the St. Lawrence and the Great Lakes. It can be caused by storm surge, large waves and high tides.

Storm surge happens when the wind associated with a major storm pushes water onto the coast. This may damage coastal infrastructure and threaten human health and safety. Large waves associated with the storm may drive additional water onshore, worsening impacts.

At times, even higher-than-normal tides can cause or contribute to coastal flooding. Coastal infrastructure in most areas is built higher than the highest predicted tide for that area. This value is known as “Highest Astronomical Tide” or HAT. Damage to coastal infrastructure typically occurs when water levels rise higher than a location’s HAT. However, if infrastructure is built below HAT, high tides alone may damage infrastructure and threaten human safety. This is especially true of unusually high tides such as spring tides, also known as king tides. Spring tides happen when the gravitational pull of the sun, moon and earth align.

If storm surge, large waves and high tides happen together, the impacts to affected areas may be significant. However, even just one of these contributing factors can cause flooding along the coast. Other factors like sea or lake ice being pushed onshore can magnify the impacts of a coastal flood.

The effects of coastal flooding can be significant and may threaten the health and safety of Canadians. They can disrupt the economies of coastal communities and cause lasting damage to coastal environments. As global sea levels rise and extreme weather intensifies, the severity of coastal flooding events in Canada is expected to increase.

Staying Safe during Coastal Flooding Events

Coastal floods can cause impacts that range from minor inconveniences to life-threatening situations. They may cause washout along roads, damage buildings or infrastructure, or accelerate coastal erosion.

It’s important to stay aware of the alerts in your area. Stay away from the coastline when there is a coastal flooding or storm surge alert and take precautionary action when required.

You can protect members of your household by learning more about floods and what precautions you can take to ensure you are prepared.

Related Links

• Coastal flooding/storm surge impact guide
• Weather Information (Environment and Climate Change Canada)
• Tidal and Water Level Stations (Fisheries and Oceans Canada)
• Coastal Inundation Forecasting Initiative (World Meteorological Organization)
• WeatherCAN Application (Environment and Climate Change Canada)
• Prepare for storm surge and coastal flooding (Public Safety and Emergency Preparedness)