Climate projection suggests warmer, wetter weather in National Capital Region by 2050

A resident works on his pump as flood waters surround his home on Friday, April 26, 2019 in Ottawa. THE CANADIAN PRESS/Adrian Wyld

OTTAWA — What could the weather in the National Capital Region look like by 2050? According to a climate change projection commissioned by the City of Ottawa and the National Capital Commission, the region could become warmer, wetter, and subject to more extreme weather events.

The projection used two scenarios: a "moderate" scenario in which global greenhouse gas emissions rise until 2040 and are then drastically cut, and a "high" scenario in which emissions are not reduced at all but, instead, continue to rise.

In each scenario, the average annual temperature is projected to rise, the number of days above 30°C is projected to go up, and the number of days below -10°C is expected to go down.

The baseline average annual temperature for all seasons is 6.1°C, according to the report. In a moderate scenario, it would rise to 8.2°C by 2050. In the high scenario, the average annual temperature would reach as high as 9.3°C.

The change would be driven in part by a dramatic rise in the number of days above 30°C. The baseline in the report is 11 days per year. That number would jump by 2050 to 32 days per year in the moderate scenario and 43 days per year in the high scenario.

The number of days below -10°C would decline. The baseline is 71 days per year. Under the moderate scenario, that number drops to 53, and under the high scenario it drops to 46 by 2050.

Shifting seasons

The projection estimates we could see later falls and earlier springs if global emissions aren't dramatically cut. By 2050, the first fall frost could come approximately two weeks later than it does now under a moderate scenario and three weeks later under a high scenario. The last day of spring frost would also come earlier by one or two weeks depending on the scenario.

The seasonal shift also means a change in the freeze-thaw cycles that can wreak havoc on city roads. The projection suggests winters could see more days around 0°C, which would lead to increased freeze-thaw cycles, offset by a decrease in freeze-thaw cycles in the fall and spring.

More rain, less snow, more extreme weather

With warmer winters, the projection expects a shorter snow season by 2050. The baseline for the national capital region is 115 days of snow cover per year. That's projected to fall to 90 days by 2050 under a moderate emissions scenario and 72 days under a high emissions scenario.

Whether the change in climate will lead to more intense snowfalls is unclear. The report shows a high degree of variability in the annual maximum one-day snowfall figures, though the moderate scenario suggests a slight increase from 20 cm to 22 cm by 2050.

The total amount of snow is expected to decrease from a baseline of 223 cm per year to 184 cm per year by 2050 in a moderate scenario and 179 cm per year in a high scenario.

The decrease in snowfall is expected to be offset by heavier, more intense rain. While the report does not project a change in the number of rainy days, it does suggest the region could see an increase of total precipitation (both rain and snow) by 2050, from the baseline of 921 mm per year to 979 mm or 993 mm under moderate or high scenarios, respectively.

The annual maximum one-day rainfall figure is expected to rise from the baseline of 37 mm to between 41 and 44 mm by 2050 under the respective moderate and high scenarios.

The warmer winters may also lead to an increase in freezing rain events. The hotter summers could lead to a rise in high humidex events. More precipitation could lead to more flooding events. Warmer, moister air also contributes to conditions that could increase the frequency of thunderstorms and resulting tornadoes.

The City of Ottawa declared a climate emergency in April of 2019.

The City says it will use the modeling and projections from the report to assess risks to health and safety, infrastructure, the economy and the local environment.

You can read the full report below.