Snow Water Equivalent (SWE, amount of water contained in the snowpack) at Whitehorse airport is nearing it’s peak for Winter 2022. While the snowpack can vary significantly from year to year, the graph above shows that there is an overall rising trend in SWE since 1966. The year-to-year variability also tends to increase, with a very dry 2019 and two consecutive years of well-above average precipitation afterward. This tendency aligns with the expected impact of climate change in Yukon.
A high SWE is also currently reported for several communities in the Territory, including in Mayo and Dawson, from where these lines are being written. Crews are working hard to manage and load that snow. The March 1 Snow Bulleting prepared by the Water Resources Branch provides additional information on snowpack. Another bulletin will follow early in April.
Like many others, our research team at the YukonU Research Centre is watching this late winter snowpack with interest. Spring conditions are upon us, and we will closely follow weather and hydrological conditions during the next few months. It is too early to confirm where and when (there is no “if”) floods will affect Yukoners, but with a substantial snowpack anomaly in many areas, it will be important to watch for weather conditions that may contribute to a rapid melt.
This blog post emphasizes property flooding, one of the first flood types that will affect Yukoners. Snowmelt-driven property flooding may represent the most significant flood risk in Yukon, not because the process is so impressive, nor because water levels are so high, but because a small amount of water at the wrong place has the potential to affect hundreds of properties in different subdivisions and communities.
What factors contribute to snowmelt-driven property flooding?
All this snow will melt or evaporate. Most of it will runoff and some of it will accumulate in terrain depressions. Runoff rates will mostly depend on air temperatures and sky conditions. The warmer the air and the clearer the sky, the faster this snow will become water. The amount of water is only one part of the equation; the other question is: where does it go? In the Spring, surface drainage can be influenced by three dominant factors:
- Ground permeability (in some areas of Yukon, the ground can hardly absorb any water, in part because it is still frozen when snowmelt begins, but also because of its characteristics, including the glacial legacy). Paved or roofed surfaces are meant to be impermeable.
- Terrain slope (if the ground is flat, it will be hard for water to find its way to lower points)
- Runoff blockage (regardless of terrain slope, water may be blocked by obstacles, including snow piles and ice)
Yukoners cannot change the state of the ground and it can be challenging to modify the slope of a property, at least in the short term. In turn, Yukoners can reduce runoff blockage as much as possible. In many areas, an effective street drainage (curbs, manholes, ditches) can only help reducing the risk of urban flooding caused by snowmelt.
How can people prepare and prevent snowmelt-driven property flooding?
Owners and tenants can consult this website from the Government of Canada or this one from the Government of Yukon. This information is general, and other proactive actions can be taken to reduce flood damage associated with snow on your property:
- Remove as much snow from your roof as you safely can. Products such as a telescoping snow rake can help you do this without going on the roof. Do not be shy to ask a friend to lend you their equipment for an afternoon. This may also prevent structural damage to your home; the snowpack is heavy and more snow could still accumulate.
- Move snow away from your property, ideally downhill, and certainly not onto other private properties.
- Dig channels in the snow, ice, and ground to drain snowmelt water away from your house. It may be necessary to install pumps to support the drainage of low-lying areas if they are close to your foundation. Ask neighbours and kids to help. Creating small rivers away from your house can also be fun. Even adults can play, and this can help reducing the flood stress.
- If nearby manholes are not free of ice and debris, clear them. If a manhole is clear but still doesn’t drain, this must be resolved by professional maintenance staff. Report blocked manholes to your community.
- If the downspouts of your house aren’t draining, slowly pour hot water on them. This hot water will melt a thin layer of ice inside the downspout and snowmelt water from your roof will find its way down. This action could be repeated during freeze-thaw cycles. THIS ONLY APPLIES IF 1. the air temperature is above freezing and 2. the excess water can flow away from your external wall with gravity (do not poor hot water on downspouts that go underground as this water will only melt a thin layer of ice before freezing and adding to the problem). Downspouts located on the north and east sides of your house are the most vulnerable to freezing in the afternoon as the sun shines from the west. Pay special attention to those, or to any downspout segments that are not exposed to the sun heat like your roof.
- If you already have heat traces installed in your downspouts, good for you. Note that you probably don’t need to turn them on for more than one hour every morning during freeze-thaw cycles.
- For houses not equipped with gutters or if gutters seem to be clogged by ice or simply not playing their role, tarps can be installed along the side of the house to drain snowmelt from the roof away from your walls and foundation. Use any material, even a small amount of snow, to provide a gradient to your surface drainage setup.
- Watch for water or ice accumulation around your house and on your property, and inspect your crawl space or basement regularly until the snowpack has largely melted. You can also install a water detector in low lying places.
- Bring valuable objects and important documents to a higher elevation or a dry area.
Keep in mind that the ground may be frozen, but your external walls are warm, and water can find its way down following a house foundation quite easily. Some foundations are made of wood and are not meant the remain humid for several days (Yukon used to be dryer). Next summer, consider changing the grade of your property, or installing a permanent pump.
In Canada, water damage has surpassed fire damage as a leading cause for insurance claims and costs to home owners. Floods may eventually dominate natural hazard risks in Yukon as well. Proactive measures such as those described above are recommended as a way to avoid damage, and protect the most valuable physical assets that most of us will ever own.
What other flood process may affect Yukoners before river ice breakup?
As the snow starts melting in small watersheds, and as the ice cover on streams begins to warm up and collapse (ice becomes softer and it will bend and break), the water carrying capacity of ditches and culverts can be exceeded. As a result, water may begin flowing on roads and highways, even under cold conditions, and this water will freeze to create what is referred to as glaciation, or road icing. The picture below was taken between Mayo and Keno in March 2022. Maintenance crews from the Department of Highways and Public Works are working hard to keep our transportation network safe. Our team at the Yukon Research Centre is supporting them by developing efficient and sustainable road icing mitigation approaches. If you are driving in the spring, be respectful to working crews, and be extremely careful, especially if traveling at night.
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This post focussed on factors that influence snowmelt-driven property flooding and road flooding and icing. Our next blog post will explore trends and factors that may contribute to other types of floods in Yukon.