It's One in a Hundred, Every Year
Think about flipping a coin. There's a 50/50 chance of getting heads each time you flip the coin. But you might actually get heads three times in a row. Or 50 times!Each year, a river may flood or not. The chance of it flooding to a certain height is 1 in 100, or 1%. But the river may have flooded that high three years in a row. Or more!
Thousand Year Event
Up on the Rouge River in Quebec, just north of the Ottawa River, there is so much flooding right now that it's a 1000-year event. Such a high water level is 10 times less likely to happen than a 100-year flood. Each year on the Rouge River, there is a 1 in 1000 chance that the water will rise this high — a 0.1% chance of it happening.Figuring Out the Chances
How do we figure out the chances of an event happening? Meteorologists (weather scientists) need at least 10 years of data to math out the chances. The more data they have (say, 30 years’ worth, for example) the more accurate their calculations are. As climate change brings us more and more wacky weather, they’ll have to keep recalculating the chances. What was once a 1000-year event may now be 10 times more likely to happen. New calculations will tell us; and they’ll have to keep redoing those calculations as the data changes.Not Just for Flooding
The terms 100-year event or 1000-year event can apply to anything: storms, cleaning you room, or having chocolate cake for dinner in the bathtub. Though that last thing might be a 1-millennium event, maybe you can make it happen this year and next.Want to learn more? There’s a thorough but a bit complex explanation on the USGS (“geological service” that studies our planet) website.
Image by Pete Linforth from Pixabay
Story by Adrienne Montgomerie
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