Calgary's Floods

23 Jun 2013 10:32 PM | Deleted user
This article was taken from the CBC's website, please click here to view the full version as well as see some amazing photos of this disaster. To donate to Canadian Red Cross, please click here.

Southern Alberta is no stranger to flooding, but this week's devastation from Canmore to Calgary and beyond was the result of a unique confluence of unexpected weather and a still partially frozen landscape unable to soak up the unprecedented deluge.

Hydrologists who watch the waterways like the Bow and Elbow rivers say several factors were at play since the rain started to fall about four days ago.

"To have these very large flood events … the stars have to line up," says Uldis Silins, a hydrologist at the University of Alberta in Edmonton.

As of 6:40 a.m. Friday, a storm system bringing rain to southern Alberta was trapped there by the Rocky Mountains, easterly winds and a high pressure system hanging over the northern part of the province. 

Most significant is a large amount of rainfall up to 200 millimetres in some places. Add in ground that is already saturated because of some more modest precipitation about 40 millimetres preceding the deluge. Combine that with areas that were still frozen not far below the surface and a local geography that encourages water to run down hill quickly, and there's a recipe for this week's devastation.

The deluges were the result of some unusual weather. Along with the torrents of rain, there were unexpected wind patterns and the convergence of two huge weather systems.

Some of the hardest-hit areas have experienced twice as much rain in 48 hours than the normal average for all of June.

The massive weather system responsible for the storms was still trapped over southern Alberta on Friday by a high-pressure system to the north and winds blowing toward the west, the opposite direction of the prevailing winds throughout Canada.

"That high pressure system is preventing the storm from moving north, and the Rockies are preventing it from moving west, so it's stuck right over the regions that are seeing the flooding," said Barsby.

"It's unusual to see a system stuck in one place for such an extended period of time."
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