MAP: Climate change to put Pitt Meadows, Richmond and Ladner at risk of major river flood

Modelling shows that dikes would be insufficient to stop a previously unthinkable flood

New maps dramatically show just how much climate change could increase the scale and impact of a major Fraser River freshet flood.

The maps, which were produced by the Fraser Basin Council and based on models that incorporated a variety of factors, suggest that while the Fraser Valley would take the brunt of any flood like that which occurred in 1894, other areas will become more vulnerable as even larger disasters become more likely as the climate changes.

In particular, Pitt Meadows and most of eastern Richmond will be at increased risk.

The 1894 flood is roughly judged to have been a one-in-500-year event, meaning that in any one year, it had a 0.2 per cent chance of occurring. But as the climate has changed, and as it is forecast to continue, an 1894-scale flood becomes much more likely. Meanwhile, the scale of a one-in-500-year flood grows considerably.

Essentially, very rare events just become rare, and outsized and extreme cases become more possible.

Although snowpacks are likely to be smaller, as the climate changes, it is expected that the snow that does exist will melt much more rapidly. More precipitation is also expected during large rain events, and two factors could significantly boost the scale of a freshet, according to Fraser Basin Council senior program manager Steve Litke.

And that has real-world consequences.

Dikes surrounding much of Pitt Meadows might protect against a flood like that which occurred in 1894, but modelling shows that higher waters that could accompany a more-extreme flood would flow around the dikes and inundate almost the entirety of that city.

Meanwhile, the dikes that protect low-lying areas of Richmond won’t be high enough to fully keep back such high flood waters, and much of the north and east of the city could end up under water. A similar fate could befall Ladner, and highly developed parts of Coquitlam and Port Coquitlam.

Although the maps released by the Fraser Basin Council are accompanied by a disclaimer saying they shouldn’t be treated of exactly where flooding will take place, they are based on extensive modelling and records of the region’s dikes.

(Click the slider in the photo below to see how climate change is expected to increase the flood risk to many areas)

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