Saskatchewan snowpack points to below-normal runoff

Thanks to above-normal temperatures that drew down much of Saskatchewan’s snowpack in January, the province now sees “below normal runoff potential” in most areas outside the southeast.

Saskatchewan’s Water Security Agency on Thursday released its 2017 preliminary outlook for spring runoff, noting the province has another six to 10 weeks of possible snowpack development.

The outlook assumes normal snowfall leading up to the spring melt, and a normal rate of snowmelt. More snow or a fast melt could also mean flooding, even in areas where below-normal runoff is now forecast.

So far, though, “many areas saw the snowpack almost completely melt or lost to sublimation in January due to above-normal temperatures.”

This melting of snowpack, however, “would have saturated the soil surface, reducing the infiltration capacity available for the melt of any late-season snow.”

A below-normal runoff might not mean reduced flood risk, the WSA added, as many regions with closed basins, such as wetlands and “terminal” lakes, are at “well above normal or record levels following several high-runoff years.”

Furthermore, the agency said, a majority of Saskatchewan was wetter than normal going into freeze-up in November 2016, so higher-than-normal precipitation going forward, and/or a “rapid” spring melt, could “significantly increase the runoff potential.”

In the province’s southeast, the WSA noted, the snowpack is “near normal, increasing to well above normal in the very southeast corner.”

For that reason, above-normal runoff is expected in the lower Souris River Basin below the province’s Rafferty and Alameda Dams, including the Antler River, Gainsborough Creek, and Lightning Creek basins.

The outlook for southeastern Saskatchewan may compound flooding worries downstream in Manitoba.

Manitoba’s latest preliminary flood forecast at the end of January found that with future unfavourable conditions, the province’s southwest, along with the Souris, Red, Pembina, Lower Assiniboine and Roseau river areas, are now at risk of major flooding.

Manitoba’s first full provincial flood outlook is expected at the end of February. — Network

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