Predicting and Alerting Coastal Flooding

New! Coastal Flooding Prediction and Alerting Program

Starting in May 2024, Environment and Climate Change Canada (ECCC) will begin implementing a comprehensive coastal flooding prediction and alerting program. This new program will allow 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 will give early warning to emergency management organizations and Canadians about the risk of coastal flooding.

This project expands our capacity to predict and alert for coastal flooding to now include:

While we will 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.

Currently, ECCC already monitors and issues alerts for regions along Canada’s Atlantic coast and the Gulf of St. Lawrence.

Long description

The pink shaded areas indicate coastal flooding coverage zones, which include areas along Canada’s Atlantic, Pacific and Arctic coasts, and the St. Lawrence. Coastlines and shorelines in the Province of Ontario are not shaded pink. Ontario’s provincial authorities continue to issue flooding warnings in the province.

Coastal Flooding Services by Province and Territory

Before this project, ECCC monitored and issued alerts for coastal flooding in Atlantic Canada and Quebec using the term “storm surge.”

Going forward, we will use the term “coastal flooding” 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 will use the term “storm surge” based on the preferences of provincial or territorial authorities.

Provinces or territories where the term “Coastal Flooding” will be used:

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

*In Ontario, provincial authorities will issue flooding alerts.

Implementation timelines of these new prediction and warning services will vary by region. The capacity to forecast and issue warnings will be available as of May 2024, but different regions will see these services come online over time.

Forecasting and Communicating Coastal Flooding Risk

With this new program, our meteorologists will be able to issue coastal flooding forecasts in all coverage zones using new 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 can assign an event a risk rating ranging from low to extreme.

To communicate the risk of coastal flooding, our meteorologists will issue forecasts using Coastal Flooding Risk Outlook maps. This information will notify Canadians early of high-impact coastal flooding events and enable informed decision-making.

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

Canadians may see these maps in the media or shared on social media by our regional forecast centers.

Long description

An example of a Coastal Flooding Risk Outlook Map. The Map shows the coastline of New Brunswick, Nova Scotia, and Prince Edward Island in detail. Along these shores, areas highlighted in the forecast are indicated by small colored polygons. The polygons are colored according to the level of coastal flooding risk: grey indicates low risk, yellow indicates moderate risk, orange indicates high risk, and red indicates extreme risk.

What is Coastal Flooding?

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What is Coastal flooding? A diagram showing the various components of a coastal flooding event. Astronomical tide and storm surge combine to create the storm tide and raise the water level along the shore. Wave action on the surface may drive water onto shore.

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.

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