INNOVATION January-February 2022

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near Lillooet, BC, that killed five people, appears to have originated from an old logging road. It was difficult to know how many of the debris flows along highways originated in burns, but some did. Extensive erosion near Tank Hill north of Lytton, BC, damaged both the rail line and Highway 1, and originated in an extensively burned watershed. Debris flows that initiate in burned watershed commonly result from rapid runoff and sediment erosion and subsequent mobilization of sediments within creek beds. The landslide that blocked Highway 7 between Agassiz and Hope originated as a rockslide that transitioned into a debris flow. This landslide swept a car off the road, resulting in injuries but, fortunately, no fatalities. LESSONS LEARNED Research continues to assess if and to what extent this storm is linked to human- induced climate change. Atmospheric rivers have affected British Columbia in the past, but the severity of this particular storm stands out: it remained stationary over population centres and river valleys that hosted critical infrastructure. Climate models project that western North America will warm by an additional 1-4°C above present-day levels by the end of this century; this additional warming will contribute to an increase in mean annual precipitation. This warming is expected to increase the likelihood of damaging atmospheric rivers during autumn. BC engineers and geoscientists need to clearly understand that climate change elevates risks posed by events such as the November 2021 storm. It is also clear that improvements are needed to warning systems for weather hazards that link meteorological conditions and the state of the land mass (e.g., snow and antecedent moisture) to the likelihood of landslides and floods.

Carefully crafted and implemented alert systems based on the best science and technology (the cell network) must be implemented as soon as possible. CLIMATE CHANGE AND INFRASTRUCTURE Expert reports warned about the vulnerability of these areas to flooding, including a report released nearly a decade ago describing the flood hazard for the Coquihalla Highway due to its proximity to steep slopes and floodplains. As British Columbia rebuilds its critical transportation infrastructure, we need an “eyes-wide-open” approach to ensure resiliency to landslides and floods in a changing climate. Much of our key infrastructure is located in river valleys bordered by steep and, in many cases, unstable terrain. Reducing risks to this infrastructure in a changing climate requires substantial capital investments and a focus on public protection and cost-benefit analyses. Critical elements include stabilizing landslide-prone engineered rockcuts along highways, avoiding slopes using tunnelling, relocating highways away from streams and rivers, installing culverts that can carry extreme flood flows, and traversing streams with bridges that will not be damaged by such extreme flows. British Columbia and Canada can look to other mountainous countries such as Norway, Switzerland, Japan, and Korea that have made substantial investments into safeguarding infrastructure and people in regions exposed to landslides and flooding. Significant upgrades to Highway 99 from Vancouver to Hope, including debris flow basins, debris nets, and removal of centre supports for bridges that could trap woody debris and lead to failure, were implemented in the 1980s following atmospheric river events that killed 11 people, and again in the lead-up to the 2010 Winter Olympics.

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The costs of upgrades are substantial, but these investments cost less over the long term than neglecting the problem and rebuilding after a disaster strikes. Registrants will also need to consider the role that extreme event cascades, such as drought-wildfires-landslides and

flooding, play in compounding flooding and landslide risks. Our disciplines encourage us to be specialists, but climate change is demanding that we recognize the interconnectedness of physical phenomena that can elevate the risk of natural hazards in a warmer world.

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