Freeze-thaw events
Note
The impacts of air freeze-thaw events, as defined here, are very difficult to distinguish from the effects of other phenomena, such as ground freeze-thaw and wintertime mild spells.
For that reason, the following sections will discuss the combined impacts of this type of episode. This page will treat “freeze-thaw events” as a combination of the various conditions mentioned, for the sake of brevity.
Freeze-thaw cycles have numerous impacts on a variety of sectors, including:
Forest ecosystems
The agricultural, wine and maple syrup industries
Winter activities
Infrastructure
Coasts
In addition, changes in the seasonality of freeze-thaw events have various consequences on the environment and the economy.
Impacts on trees
The impacts of freeze-thaw events on forest ecosystems are complex and difficult to quantify, as they are influenced by many factors, including snow cover.
The decrease in snow cover caused by warming temperatures exposes tree roots to freezing, making them more vulnerable to damage.
The impacts on trees vary depending on when a freeze-thaw episode occurs. For example, they will be different if it occurs during dormancy rather than at the beginning of the growing season. The impacts on trees are greatest when freeze-thaw events happen at the start of the growing season, because that is when the tree is growing, unlike the dormant period, when physiological activity is lower.
The severity of freeze-frost events is influenced both by the duration of the event and the temperature differential. The freezing tolerance of trees also varies considerably from species to species, so the effects on their health and survival are highly variable.
This webinar shows how climate change is affecting the frequency and intensity of freezing events in northern ecosystems, such as Quebec’s temperate and boreal forests. This change in the freezing regime may damage trees and reduce forest productivity. Tree damage by freezing is likely in the future climate and should be considered in forest management plans for adapting the forestry industry to climate change and in assisted migration programs.
Impacts on maple syrup production
The sugar maple tree is an emblem of Quebec culture. However, several climatic factors can disrupt maple syrup production, including the seasonality, duration, frequency and intensity of freeze-thaw events and winter and spring warm spells.
The sap for syrup production is usually harvested in spring, when the temperature rises above 0°C during the day and falls below freezing during the night. However, due to the earlier advent of freeze-thaw events, the sugaring off season could occur earlier in the spring and during the winter.
Changes in the timing and variability of freeze-thaw episodes may have an impact on overall maple syrup production.
Freezing and thawing
Injuries related to the ground freezing can have negative effects on sugar maple health, including:
Obstructing the flow of sap
Reducing total sap production
Reducing the amount of sugar produced per tree in the spring
Frequent thaws in the winter may also compromise the vitality and survival of the trees. Between 1985 and 2006, the quantity of syrup obtained per tap generally decreased in Quebec.
Rising temperatures
Rising temperatures can also extend the growing season of sugar maples, promoting their growth and increasing their productivity. However, if the freezing period gets too short, it may disrupt the natural process of maple sap production. In addition, the increase in temperatures may lead buds to open earlier, also shortening the production period.
This research project has identified the main issues and impacts of climate change with regard to the shifting of the season and the yield per tap in Canadian and American maple sugar bushes. Maple syrup production is one of the economic activities most directly related to the climate, and in particular to the springtime weather.
Impacts on winter activities
Due to the poorer snow quality when freeze-thaw events occur, winter activities like snow tubing, cross-country skiing and alpine skiing may also be disrupted.
When snow melts and freezes repeatedly, an ice crust forms on the surface of the ground, significantly affecting the quality of the snow. The snow can become granular or turn into very wet snow. This makes some activities difficult, and avalanches may occur in some areas due to the fragile layers of ice in the snow.
Impacts on agriculture
Exposing plants to temperatures above 0°C during the winter can reduce their tolerance to cold, making them more vulnerable. With climate change, an increase in the risks associated with the loss of winter hardiness in plants is anticipated. This is due to the probable decrease in snow cover, which will no longer be sufficient to insulate perennial forage plants from freeze-thaw events.
The change in the seasonality of freeze-thaw cycles could also affect the growing season of plants, with the first frost coming later in the fall and the last frost earlier in the spring. However, it should be noted that this change in the length of the growing season will make it possible to choose later-maturing cultivars or hybrids and to cultivate new species.
In the winter, the reduced snow cover and the increase in precipitation in the form of rain may threaten perennial plants and crops. Winter freeze-thaw cycles accompanied by rains may also increase the weight of snow and ice on farm buildings.
With less snow and a shorter period of snow cover, soils will be more exposed to wind and temperature variations. However, extreme cold spells are projected to be less frequent and less intense.
Impacts on vineyards
Freeze-thaw events are a challenge for wine growers, as they can influence grape production, quality, and yield. In particular, they can lead to variations in the availability of water in the soil, causing water stress for the vines. Excessive water stress can affect grape growth and wine quality.
In the spring, freeze-thaw events can damage buds, shoots and young leaves, reducing yield and affecting grape quality.
In the fall, late frosts can delay the grapes’ maturation by extending the growth period, affecting the sugar and acid content of the grapes, and ultimately the taste of the wine.
Impacts on infrastructure
Since air freeze-thaw cycles are closely linked to events in the ground, they can have significant impacts on the built environment. One of their most well-known effects is the deterioration of road infrastructure.
When ice melts, water can seep into the various layers of structures. When this water refreezes, it expands, causing cracks and the lifting of surfaces, resulting in potholes, among other things.
Freeze-thaw events in the ground can also accelerate the degradation of wood, weaken stone foundations and affect masonry. Combined with the use of de-icing salts, these events can increase metal corrosion.
Figure 1: Illustration of the process that leads to the creation of a pothole during a freeze-thaw event. Source: Ville de Saint-Eustache
Liquid precipitation in the winter and infrastructure
Due to the increase in winter precipitation in the form of rain, freeze-thaw events significantly accelerate the degradation of buildings and roads. This leads to additional costs for infrastructure maintenance, repairs and modernization.
Coastal and cliff erosion
The friable cliffs and clay banks found in the Magdalen Islands and along the North Shore of the Saint Lawrence River, for example, make these areas sensitive to freeze-thaw cycles.
During freeze-thaw cycles in spring and fall, water seeps into cracks in vertical surfaces when the temperature is over 0°C. When temperatures drop below freezing, the water freezes and expands. This increase in volume may cause part of the vertical surface to detach.
Depending on the amount of sunlight and the orientation of the cliffs, the surfaces can warm up enough to cause the water inside the cracks to thaw, even at air temperatures as low as -23°C. That means a reduction in soil cohesion can occur at temperatures below 0°C.
