Will Ontario’s warm December affect spring flooding?

A flooded cabin By Pascal Huot/Shutterstock

Experts are warning Ontario residents to prepare their properties for floods amid record-setting global temperatures. A report by the Copernicus Climate Change Service, which analyzes global climate for the European Union, found 2023 was the “warmest calendar year in global temperature data going back to 1850.” Environment and Climate Change Canada suggests 2023 was “very likely to be the warmest year in possibly 125,000 years.”

Dr. Anabela Bonada is the manager of Intact Centre on Climate Adaptation, a University of Waterloo research centre dedicated to reducing the impact of climate change. She says Ontario’s warm December led to less snowpack—the layers of snow that harden due to months of cold temperature. “If we have less snow and we start to get the rain early in spring, the rain saturates the ground, and it can lead to flooding and increased levels of the lakes,” she says.

Bonada says the warm weather may also lead to more extreme rain events. Cities with pavement and other unnatural grounds that can’t absorb water are most susceptible to these events, but there are several factors that also put natural cottage environments at risk.

“Even if we do have a really great marshland to absorb the rain, it might not have seen as extreme a rain event as we’re seeing now,” she says. “Rivers were also meant to grow during floods, but now where it’s supposed to grow, we’ve built properties or roads.”

Nathan Manion is the founder of the sustainability consulting company Greenscale. He says a large amount of rain in late winter, followed by a dry spell, would make the ground less capable of absorbing water again. He says rain-related floods will be more likely where there’s development—namely, in southern Ontario.

“The main takeaway from this is that climate change is warming our environment, and that makes all our normal weather patterns very hard to predict,” Manion says.

Bonada says this unpredictability makes it difficult to determine the effect of December’s warm weather in the spring, but floods are becoming more frequent on average due to climate change. As a result, she recommends residents take precautions as though their homes are already at risk of flooding.

Cottage Q&A: Basement flooding damage

Cheaper measures include removing leaves from gutter and drainage systems when opening or closing the cottage, and extending downspouts around two metres away from the property. Installing back water valves and sump pumps with a backup generator, or grading the property so water drains away from the foundation, usually costs more than $250, but she says they’re worth the price. “Even if it’s $1,000, how much more would it cost if you did have a flood?” Bonada says. “Basements, on average, cost $43,000 for the homeowner to fix.”

An update on spring flooding in Ontario cottage country

Manion says installing brick or gravel driveways in the place of paved driveways would allow water to disperse more efficiently. So would maintaining the natural shoreline of a property.

And in the event of a flood, Manion and Bonada recommend contacting local conservation authorities.

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