Province downgrades flood risk due to slow melt, average precipitation

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This article was published 25/03/2022 (1460 days ago), so information in it may no longer be current.

Average precipitation and slowly melting snow are working in Manitoba’s favour right now, changing the outlook for the southern part of the province.

“So far, the past two weeks the weather has been very favourable, as there has not been any significant precipitation and the temperatures have been staying near zero,” Fisaha Unduche, the province’s executive director of hydrologic forecasting and water management, said Friday.

Manitoba’s Hydrologic Forecast Centre is now predicting a flood event near 2017 levels, a downgrade from last week’s forecast of levels closer to 2020.

“These conditions are allowing for a very gradual melt, reducing the runoff as the water has time to absorb into the ground,” Unduche said.

Frost depth is near zero in most central and southern basins, allowing the gradual absorption of the melt, while short-term weather forecasts are favourable, with temperatures set to drop below freezing until April 1 and hover around that mark for another week without any significant precipitation.

“This is very good news because Mother Nature has been co-operating very favourably,” he said.

Last week, the province had predicted a high risk of major spring flooding along the Red River with levels similar to 2019 with favourable conditions, and levels similar to 2020 under normal conditions.

Based on the centre’s updated forecast, Unduche said the Red River will peak twice this flood season. The first is predicted to reach Emerson between March 30 and April 2 and then hit Winnipeg between April 3 and 5. Levels are predicted to be well below the banks.

The second peak is expected between April 10 and 20 as a result of the snow melt in the Manitoba basins, hitting Winnipeg between April 12 and 22.

Overall, Unduche said there is a risk of moderate flooding for the Red River, a low risk for the Assiniboine, Souris and Pembina River basins, a minor to moderate risk in eastern Manitoba and a low risk in the North.

Most lakes in Manitoba are expected to remain in their desired operating ranges following the spring runoff and the risk of flooding in the Interlake is low, he noted. However, ice jam-related flooding remains a concern.

Ice-breaking work has been completed on the lower Red River and the Icelandic River and work is scheduled to begin on the Portage Diversion outlet today.

Unduche said he expects the Red River floodway will have to be used, as will the Portage Diversion.

Within Winnipeg, the Red River is expected to reach between 15.5 feet and 20 feet at James Avenue, depending on future weather.

Going forward daily updates will be provided on the flood forecast on the Hydrologic Forecast Centre’s website, Unduche said.

Emergency Measures Organization director Johanu Botha said evacuation and emergency social services plans have been confirmed with municipalities across Manitoba in anticipation of a flood event contrary to the current “rosy” forecast.

“We will maintain a number of tools for all our emergency management partners to ensure flood response in this province remains streamlined and co-ordinated,” Botha said. “We’re ready should it be required to activate the Manitoba Emergency Coordination Centre, which will allow us to co-ordinate a large provincial response.”

Unduche said in a normal season Manitoba would receive about 80 millimetres of precipitation between now and the end of May, with his office expecting about 70 millimetres to fall in that time.

Higher precipitation levels and rapid snow melt would push flood projections into an unfavourable weather scenario, with flood levels between the 2017 and 2013 peak levels at Emerson.

“With 90 per cent confidence, levels will be as predicted,” Unduche said. “Manitobans should be assured that with 90 per cent probability our flood risk is downgraded in most basins.”

danielle.dasilva@freepress.mb.ca