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Course:CONS200/2026WT2/Environmental and social impacts of the 2021 flooding season in southern BC

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Environmental and Social Impacts of the 2021 Flooding Season in Southern BC

Introduction

Flood devastation over Abbotsford and Chilliwack BC following the atmospheric river that took place in mid November. November 23, 2021.

During November of 2021, Southwestern BC experienced unprecedented rainfall that caused catastrophic flooding. The flooding caused widespread damage to infrastructure, agriculture, communities and ecosystems. The event resulted in damage to 1,000 farms, 15,000 hectares of land, 2.5 million livestock, and disrupted British Columbia’s road and railway infrastructure [1]. Further impacts such as floods and landslides resulted in the loss of at least five lives. For an extended period of time, Vancouver was effectively cut off from the rest of Canada by road and rail, making the event the costliest natural disaster in the province's history [2]. The flooding was driven by a powerful atmospheric river that produced two days of intense rainfall, which overwhelmed regional drainage and flood control systems that were not designed for such extreme precipitation events. The many effects of climate change likely increased the intensity and likelihood of the event [3], as well as the likelihood of similar events occuring in the future, highlighting the need for improved mitigation measures and informing policy changes aimed at reducing future flood risks.

History of the Sumas Prairie and its Colonization

The Sumas prairie has undergone drastic changes to appear the way that it does today. Historically, the eastern part of the Sumas Prairie was occupied by Sumas Lake, before its eventual draining for agricultural purposes between 1920 and 1924. Farmers sought the fertile soil at the bottom of the lake[4].

Before its draining, Sumas Lake saw much natural variability, which was caused by the Lake's connection to the Fraser River, which is in turn connected to the Pacific Ocean. The water levels of the Fraser River typically rise in the summer due to snowmelt. This unpredictability in the Fraser directly translated to the Sumas Lake, with the water levels of the Lake seeing large changes in depth and size depending on the season, snowmelt, and even the Pacific tides [5].

The Stó:lō people are an Indigenous group that have historically inhabited the Fraser Valley for at least 4,000 years. They had a deep connection to Sumas Lake, both for cultural purposes and for fishing. In 1858, the discovery of gold in the Fraser Valley meant that the Stó:lō were forced into reserves by James Douglas, British Columbia's governor [5]. In the 1970s, there began to be discussion and legislation surrounding diking the Sumas Lake due to its unpredictable behaviour. By 1920, the conversation had shifted towards draining the lake, with hopes of accessing the fertile soil at the bottom of the Sumas Lake and avoiding its unpredictable shifts. By June 26, 1924, Sumas Lake was gone; it had been drained [5]. Today, the lake remains drained and is mostly covered by agricultural lands.

Converging Factors and Causes of Flooding

Atmospheric rivers are long and narrow filaments of concentrated water vapour, typically found in wetter west coast regions [6].  They often produce heavy rainfall when the moist air is forced upward by mountains or other rising air currents. [6]. These conditions contributed to the extreme rainfall and flooding in southern British Columbia in November 2021. Historically, westerly atmospheric river events of this magnitude are approximately one in ten year events in the region's current climate. Human-induced climate change has increased the likelihood of such events by at least 60% [2], and studies indicate that the probability of extreme streamflow events in October–December has risen by an estimated 120–330% due to human influence [3].

In addition to the unprecedented atmospheric river, Sumas Lake was a contributing factor to the severity of flooding. Between the Sumas Mountain and Vedder Mountain in the Lower Fraser Valley, Sumas Lake was historically the center of a dynamic floodplain landscape [7]. The Indigenous food system in the area was supported by a high amount of animal and plant life [7]. In addition to its biodiversity, the lake could vary from an area of 9,000 acres (3,642 ha) and a depth of 3 meters in the winter, to an area of 26,000 acres (10,522 ha) and depth of 11 meters in the spring [7]. During the past 150 years, the Lower Fraser has seen changes within its vast network of rivers, creeks, wetlands, and floodplains. These ecosystems have been developed into a series of ditches, canals, dikes, floodgates, and agricultural fields, in an effort to further residential and urban development in the area [7]. The changes in the lake's historical wide array of seasonal depth and the progression of urban development resulted in 30% of native vegetation remaining intact and over 85% of floodplain habitat and 64% of streams being lost [7]. In the early 1920's, The Sumas Lake was drained after an act in a Canada-wide process of land dispossession from Indigenous peoples in Canada [7]. The loss of traditional use and knowledge resulted in mismanagement practices that increased the flood risk in the area. By the mid 1920's, a plan was put in motion to drain the lake in order to further expand agricultural practices in the area. By 1924, the Chilliwack River had been diverted west, draining the lake through the Sumas Drainage Canal and into the Fraser River around the northeastern tip of the Sumas Mountain [7]. Despite the loss of the lake, the low elevation remained, resulting in permanent flood risk for the newly developed agricultural area.

Impacts

The flooding caused by the 2021 atmospheric river had severe impacts throughout British Columbia. These include impacts on British Columbia's major industries such as agriculture and the transportation of goods, causing severe damage to both the environment and infrastructure in surrounding areas, in addition to creating public safety and human health risks.

Human Impacts

During the floods and resulting landslides, five individuals were confirmed dead and over 3,000 residents were forced out of their homes and evacuated in the Abbotsford area alone [7]. In the Sumas Prairie, the former Sumas Lake refilled, displacing thousands and destroying homes built on the historic lake bed [7]. Farms, homes, businesses, and transportation corridors flooded, causing destruction to livelihoods and infrastructure. Many of those affected by the flooding were not aware that their homes and farms were located on a former lakebed.

Floodwaters transported significant amounts of debris, sediment, and bacteria. E. coli counts at several locations, such as the Pitt Meadows Shoreline, exceeded Canadian Drinking Water Quality Guidelines (CDWQG) following sanitary sewer overflows [8]. Sanitary sewer overflows (SSOs) and the overflow of septic systems led to dangerous spikes in bacteria and other waterborne pathogens which pose risks to human health [8].

Due to the flooding, many were forced to stay home and not travel within the flooded region for extended periods of time. For many days during November of 2021, using smartphone tracking data, it was found that there was virtually no travel between the cities of Hope, Merritt, and Chilliwack (all three are within the Fraser Valley and were affected by the floods)[9]. In the following weeks, travel between the cities slowly began to increase, but it took extended time for typical travel between the cities to return.

Environmental Impacts

The floods severely degraded the Lower Fraser Valley's critical habitat, which is essential for Pacific salmon and sturgeon. Rapidly rising waters caused massive sediment movement which buried salmon spawning grounds and destroyed eggs. Scientists note that the full impact on salmon populations may not be known until their 2 to 5 year life cycles are complete in spawning season of 2026 [10].

Excessive nutrients (mainly nitrogen and phosphorus) washed into slow moving bodies of water from farmland, leading to eutrophication. Eutrophication occurs when nutrient runoff (often from agricultural fertilizers) causes rapid algal growth. When the algae dies, the bacteria that decompose the algae consume dissolved oxygen, creating hypoxic (not enough oxygen) conditions. These hypoxic conditions can suffocate aquatic organisms [11].

The death of over 670,000 farm animals created a biological hazard through an increase of immediate groundwater contamination and the spread of disease [12]. Crews eventually removed over 16,000 metric tons of natural and man-made debris (including 98 vehicles and 4 bridges) from provincial waterways to prevent further ecological blockages from occurring as a result of the floods [12].

Operators remove boulders from the bottom of a cliffside, in response to flooding and mudslides. Merritt area, March 23, 2022.

The flooding not only contributed to land destruction, but had severe impacts on rivers and natural water systems. The unprecedented rainfall contributed to the destabilization of slopes, erosion on shorelines, and damage to critical infrastructure such as dikes and highways. Extensive human made debris was dispersed across multiple waterway systems. Among the debris, entire homes and buildings were washed into river streams, along with vehicles, propane and fuel tanks [13]. Additionally, rivers experienced pollution through shipping containers and damaged bridges, further contributing to environmental degradation. The impacts of the debris posed risks to public safety, water quality, and infrastructure. In addition to human made debris, waterways experienced extensive damage through the distribution of natural debris. Rivers were affected by the runoff of logs and fuel left by wildfire, uprooted trees due to erosion, along with the accumulation of rocks and boulders in river beds [13]. With the presence of natural debris, buildups obstructed water flow, compromised the structure of many waterways and increased risk to further damage in the future flooding events.

Economic Impacts

The British Columbia provincial government estimated that BC's farmers lost approximately $285 million in flood-related damages [1]. This estimate took all of BC's various agricultural sectors into account, including how many acres of plants were lost, losses of cattle, losses of homes on farms, and the tens of thousands of hens lost in flooding. It is also key to highlight that the damage goes beyond the crops and cattle lost during the flooding as the farmland itself may suffer from long-term damage [1]. In addition to flood damage to farmers, the Insurance Bureau of Canada reported an estimated $9 billion Canadian dollars (CAD) in insured damages, contributing to the further economic impacts [14]. The repairs required to fix widespread power outages added to further economic damage.

Large impacts of the flooding was also seen on British Columbia's roads. In 2023, the British Columbia Transportation Ministry said that it was expected that the repairs for major damages to BC's highways had grown to approximately $1 billion. At the time, $250 million in repairs had been done on highways one (the Trans-Canada highway), five, and eight. However, more repairs were needed to restore the British Columbia's highways and attempt to make them more resilient to future atmospheric rivers and flooding, which is why Rob Fleming, BC Transportation Minister, estimated that the government would likely end up spending around $1 billion in highway repairs [15].

The Trans-Canada highway, which spans from British Columbia to Newfoundland and Labrador, is Canada's main route for transporting goods across the country. The highway suffered immense damage during 2021's floods, interrupting the key transportation route through BC [1]. In addition, the flooding made transporting goods to and from the Port of Vancouver increasingly complicated. The Port of Vancouver is a key Canadian asset for international trade, and its disruption had negative effects on Canada's federal economy.

Government Response and Recovery Efforts

The provincial government of British Columbia declared a state of emergency and implemented a variety of disaster responses to respond to BC's 2021 floods. This prompted organized activity across many levels of the Canadian government, which includes municipal, provincial, and federal agencies coming together to discuss the best strategies to manage the crises and mitigate the flood impacts. The different levels of the Canadian government came up with many ways to respond with recovery and evacuation plans as well as emergency response units to address damage to infrastructure, the environment, and the evacuation of affected communities . Initiatives from the provincial government focused on post-flood repair and clean up by implementing flood debris management programs to restore and improve waterways [12].

Construction underway to restore river structure in response to flooding and mudslides in the Merritt area, March 23, 2022.

A project by the government of BC, which was coordinated with Indigenous groups, conservation organizations, and local agencies, which was titled: "Recovering Together: November 2021 Atmospheric River" [13], assessed environmental, public safety and infrastructure, cultural aesthetic and community values along with stability and long-term risk assessments. In response to these assessments, debris from hard to reach areas was removed to avoid hazards posed to ecosystems, water quality and wildlife [13]. In addition to these hazards, accessible debris that posed threats to downstream communities and infrastructure was also removed. Along with debris that obstructed water flow, impacted flood control systems and disrupted land stability [13]. After actions were carried out, the province reported that sediment debris in water bodies contributed to significant erosion and shifting slopes along waterways [13]. These findings brought researchers to the conclusion that the material deposits altered the shape and slope of watercourses, in turn creating hazards that increased the risk to public safety. These risks were summarized as potential for future flooding, unstable banks and navigational challenges [13]. Due to these findings, 128 sediment sites were assessed, with 17 project locations being approved for emergency response action [13].

The federal government made an especially significant contribution in supporting recovery through the Disaster Financial Assistance Arrangements (DFAA) program. This program from the Government of Canada contributed over $1 billion to help cover costs caused by the 2021 BC floods, including an additional $556,955,800 in 2023 to continue the ongoing relief efforts [16]. The money was not only used to restore public services and infrastructure, but also supported evacuation protocols, individual aid, farmland, and small business owners to mitigate economic and environmental impacts. The Government of Canada stated that they were devoted to Canadian citizens and will do as much as they can to help citizens prepare for and resist any future extreme weather events [16].

Minister Kelly Greene and Minister Lana Popham meet with Abbotsford Mayor Ross Siemens and technical experts to give the latest update on flood response in British Columbia. Following the update, Minister Greene and the Mayor toured areas impacted by the atmospheric river and the emergency operations centre. December 12, 2026.

Water quality assessments were conducted by researchers and the government to evaluate and record potential pollutants in the water within the Fraser River Valley area after the floods. Floodwaters can carry contaminants from excess sediment, agricultural runoff, and other sources which can negatively impact surrounding environmental and human health. Additionally, the research group wanted to determine if the flood event caused accelerated pollution of contaminants compared to average rainfalls to track changes in water composition, ensuring that contamination levels do not further worsen beyond expectations [8].

Infrastructure of highways and railways where prioritized for repair from flood and landslide damage by the government as they were critical transportation and trade routes. Repair crews often had to reconstruct entire sections of highways due to erosion while reinforcing them to prevent similar events from happening in the future by implementing reinforced structure and better drainage systems. These repairs reconnected the Lower Mainland with the rest of Canada, reactivating supply chains [1].

Future Recommendations and Preventative Measures

Following the recovery efforts, several preventative measures were put into place in order to prevent further flooding across British Columbia's lower mainland - from upstream of Fraser Valley all the way down to the Pacific Ocean [17]. The most widespread measure used across this area is dikes, large engineered barriers intended to prevent flooding by either containing water or separating the water from the land. Despite numerous dikes being in place, Principle Flood Management Engineer Monica Mannerström noted that a study found 87% of dikes to be "in less-than-fair condition" and that 71% simply wouldn't hold in the event of a flood, rendering them useless [17].

Along with the dikes, a water pump system upgrade was deemed necessary in order for the location to be floodsafe going forward. Despite having this knowledge for many years, there has been no action to actually improve upon the current status of the different measures in place. Part of the reason that no real progress has been made to upgrade the preventative measures is because according to the Mayor of Abbotsford, Henry Braun, the cost of operations to meet the provincial design standards would range from $2.5 billion to $2.8 billion [17].

Premier David Eby, Minister Kelly Greene, Minister Lana Popham and others visit Abbotsford on December 15, 2026.

The largest shift in preventative measures following the floods occurred in 2024 when the province moved from "reactive" emergency response and towards "integrated flood management" [18]. The introduction of the BC Flood Strategy in May 2024 led to more coordinated and long-term flood risk management, and re-enforces British Columbia's position that significant flood management duties (such as diking authority) should be assigned to local governments [18]. Despite this seemingly large step in the right direction, failure to properly fund the strategy has exposed the gap between intentions and actual action being made to mitigate damage and protect communities from flood events. This failure to fund the new program, along with failure to fund improvements for the dikes and water pumps suggests that the province is not willing to allocate enough funds to this issue, despite the risk it proposes to citizens of British Columbia.

Central to this strategy is a transition toward watershed-based planning, which shifts the primary focus from isolated local infrastructure to the hydrological health of entire river basins [19]. This approach prioritizes "Room for the River" tactics—such as the implementation of setback dikes and the restoration of natural floodplains—to reduce water velocity and peak surge levels before they reach urban centers [20]. By integrating nature-based solutions like wetland preservation and upper-watershed forest management, the province aims to utilize natural landscapes as biological sponges to mitigate runoff [19]. However, the successful execution of these plans requires unprecedented cross-jurisdictional cooperation between municipalities and First Nations, as well as sustained provincial funding to move beyond theoretical modeling and into physical land-use changes [19].

References

Note: Before writing your wiki article on the UBC Wiki, it may be helpful to review the tips in Wikipedia: Writing better articles.[21]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Senate of Canada (October, 2022). "Treading water: The impact of and response to the 2021 British Columbia floods". Retrieved March 8, 2026. Check date values in: |date= (help)
  2. ↑ 2.0 2.1 Gillett; et al. (27 April 2022). "Human influence on the 2021 British Columbia floods". Retrieved 8 March 2026. Explicit use of et al. in: |last= (help); Check date values in: |archive-date= (help)
  3. ↑ 3.0 3.1 Environment and Climate Change Canada (March 2021). "Human influence on the 2021 British Columbia floods". Retrieved 8 March 2026.
  4. ↑ "Sumas River and Canal". Government of British Columbia. January 7, 2025.
  5. ↑ 5.0 5.1 5.2 Murton, James (January 2008). "Creating Order: the Liberals, the Landowners, and the Draining of Sumas Lake, British Columbia". Environmental History – via ProQuest.
  6. ↑ 6.0 6.1 Ralph; et al. (01 April 2018). "Defining "Atmospheric River": How the Glossary of Meteorology Helped Resolve a Debate". Retrieved 8 March 2026. Explicit use of et al. in: |last= (help); Check date values in: |date= (help)
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Finn; et al. (02 June 2024). "Reclaiming the Xhotsa: climate adaptation and ecosystem restoration via the return of Sumas Lake". Retrieved 08 March 2026. Explicit use of et al. in: |last= (help); Check date values in: |access-date=, |date= (help)
  8. ↑ 8.0 8.1 8.2 Minton; et al. (June 2022). "Water Quality Assessment of the Fraser River Following the November 2021 Floods" (PDF). Retrieved 09 March 2026. line feed character in |title= at position 55 (help); Explicit use of et al. in: |last= (help); Check date values in: |access-date= (help)
  9. ↑ Liao, Enqi (May 24, 2024). [doi.org/10.32866/001c.117422 "Travel Behavior during the 2021 British Columbia Floods Using De-identified Network Mobility Data"] Check |url= value (help). Resilience Findings.
  10. ↑ DFO (2022). "Extreme environmental impacts on Pacific salmon". Retrieved 09 March 2026. Check date values in: |access-date= (help)
  11. ↑ Ross; et al. (November 2022). "A lake re-emerges: Analysis of contaminants in the Semá:th X̱ó:tsa (Sumas Lake) region following the BC floods of 2021". Retrieved 09 March 2026. Explicit use of et al. in: |last= (help); Check date values in: |access-date= (help)
  12. ↑ 12.0 12.1 12.2 Province of British Columbia (2024). "Flood debris management projects". Retrieved 09 March 2026. Check date values in: |access-date= (help)
  13. ↑ 13.0 13.1 13.2 13.3 13.4 13.5 13.6 13.7 Government of British Columbia. "Recovering Together: November 2021 Atmospheric River". Retrieved 12 April, 2026. Check date values in: |access-date= (help)
  14. ↑ S. Richards-Thomas, J. Déry, E. Stewart, M. Thériault,, Tamar, Stephen J. Déry, Ronald, Julie (12 June, 2024). "Climatological context of the mid-November 2021 floods in the province of British Columbia, Canada". Retrieved 10 April, 2026. Check date values in: |access-date=, |date= (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  15. ↑ Garrett, Catherine (February 7, 2023). "B.C. highway flood repair costs expected to balloon to $1 billion". Global News. Retrieved April 11, 2026.
  16. ↑ 16.0 16.1 Canada, P.S. (2023, February 23). "Government of Canada provides disaster recovery funding to British Columbia for 2021 flood". Retrieved April 10, 2026. Check date values in: |date= (help)
  17. ↑ 17.0 17.1 17.2 Senate of Canada (October, 2022). "Treading water: The impact of and response to the 2021 British Columbia floods". Retrieved March 8, 2026. Check date values in: |date= (help)
  18. ↑ 18.0 18.1 "Recurring flood risk requires sustained response". UBCM. December 17, 2025. Retrieved 12 April 2026.
  19. ↑ 19.0 19.1 19.2 Ministry of Water (March 21, 2024). "From Flood Risk to Resilience: A B.C. Flood Strategy to 2035" (PDF). gov.bc. Retrieved 12 April 2026.
  20. ↑ City of Merritt Flood Mitigation Department (November 18, 2025). "Dike 129/130 Program: Setback Dikes and River Corridor Management". Merritt Flood Mitigation. Retrieved 12 April 2026.
  21. ↑ En.wikipedia.org. (2018). Writing better articles. [online] Available at: https://en.wikipedia.org/wiki/Wikipedia:Writing_better_articles [Accessed 18 Jan. 2018].


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