Manitoba revises flood risk outlook
By Manitoba Government news release
Mar. 28, 2013, Winnipeg, MB - The Manitoba Infrastructure and Transportation Hydrologic Forecast Centre's second 2013 flood outlook calls for increased spring flooding potential on the Red, Souris, Pembina, Assiniboine, Saskatchewan and Qu'Appelle rivers, and in the Interlake, due to additional March snowfall, above‑average snowpack with high water content in many parts of the province, and low temperatures that are keeping frost in the ground longer than normal.
Provincial forecasters say, while these conditions have increased the risk of flooding to moderate to major, up from minor to moderate as forecast earlier this year, the current outlook does not foresee prolonged river flooding and high lake levels as in 2011. The outlook has trended towards the 2009 flood in the Red River Valley and the Interlake.
In addition to heavier-than-average snowfall, which was 200 per cent of normal in much of Manitoba, Saskatchewan and North Dakota this month, provincial forecasters have concluded that cooler‑than‑normal temperatures have increased the depth to which soil remains frozen. Across southern Manitoba, soil is frozen to a depth of between 50 centimetres (1.5 feet) to more than 100 cm (three ft.), mainly due to prolonged periods of very cold temperatures. Frozen soil does not absorb meltwater as easily as thawed soils, and it can increase spring run-off and overland flooding.
The colder-than-normal temperatures will also cause a later spring melt, which increases the likelihood of a rapid melt. Cool temperatures later into the year also increase the likelihood that the melting snowpack and normal spring rains will occur at the same time.
While all these factors have increased the risk of flooding to moderate to major, conditions can change quickly and the outlook is still very dependent on weather conditions from now until the spring melt.