B.C. officials watching for impact of ‘extreme’ heat on floods

Temperatures are expected to rise close to 30 C in Southern Interior, threatening hasty snowmelt

The Okanagan region has been reduced from a flood warning to flood watch by the B.C. government, but that could change in short time as hot weather melts a heavy snowpack.

Meanwhile, the B.C. River Forecast Centre is watching for potential for flooding to “come back up again” on the already battered Boundary region. Up to now, 2,500 properties have been evacuated in that region and Grand Forks lost power this week.

So far, Chris Duffy with Emergency Preparedness B.C. said there are 23 states of local emergency, 10 band council resolutions and nine First Nations have emergency operations centres opened. Three reception centres have been opened for evacuees.

On that note, 31 evacuation orders affecting 1,993 homes have been issued and 36 evacuation alerts affecting 930 homes. Over two million sandbags and 10 sandbag machines have been delivered in the province, with help from 210 B.C. Wildfire Service personnel.

“For us the flood warning is that we expect the breaching of the river banks is either occurring or imminent, and on a number of areas on the Okanagan, we saw rivers come up to that level on Wednesday night, Thursday,” said Dave Campbell with the B.C. River Forecast Centre on the reduction of flood risks in the Okanagan.

“For example, Mission Creek came up to about 120 cubic metres a second, and that’s now dropped down to the order of … about 55 cubic metres a second. So in the short term that immediate flood risk is not there. As we turn into this warming trend, if we start to push those levels … we would upgrade it again to a flood warning.”

In a media conference call Friday morning, officials said ongoing high temperatures — averaging 5 C above normal — can be considered extreme weather, due to the lengthy period of time.

“(It was) in some ways, a kind of worst case scenario if conditions — leading into that, very warm weather over the past week and then followed by fairly heavy rainfall. Upwards of 50 millimetres of rain over about a day-and-a-half period through many areas of the North Okanagan, Okanagan and over into the Boundary country.”

That came with an “extremely high” snowpack in the region, which has been measured at about 150 per cent of the historic normal. Despite a cooler early spring, the hotter weather more recently has begun melting that snowpack, but Campbell said there’s still plenty to come.

Only about five to 20 per cent of the snowpack has melted in higher elevations in the Southern Interior, compared with about 30 to 50 per cent of the snowpack in lower elevations.

“A number of rivers, on the preliminary side of things, got up into the 100-year return period level, or above,” Campbell said, cautioning that the statistics have not been verified yet.

“We’re in a bit of a holding pattern right now. If you look at the weather, the wet weather’s worked its way through. Things are easing slightly, and so we’re putting our heads toward the next phase of weather that’s coming at us.”

That’s that hot weather expected to rise to the upper 20s C, and not dropping likely at least until mid-week next week, but potentially into the end of next week. Campbell said the next few days will be a gradual build up to a point that may draw concern.

“For a number of areas we’re kind of at that cusp, or near that cusp, of is there enough snow to keep these rivers high. Where we’ve got areas that are a higher elevation, there’s absolutely enough snow for that,” Campbell said.

“When we’re in the lower elevations, we’re melted out now, and we’re sort of in that middle-elevation zone that we’re maybe a little more uncertain just how this hot weather is going to influence things.”

To the south, Osoyoos Lake continues to fill — in the early hours of Wednesday morning, it appears to have held steady, before spiking somewhat later on in the morning. That lake is still a little under a foot below the record depth of 917 feet.

Similar to other areas, Campbell said officials are watching how the snow melt from high temperatures will affect the water flowing into the lake, which is drained into the U.S. Control over how that water is drained is run south of the border.

“The question is how much can we squeeze out of this before we get to that point, and I think that’s a bit of uncertainty,” Campbell said.

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Dustin Godfrey | Reporter

@dustinrgodfrey

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