Compound hazards are defined as situations where multiple extreme events occur either simultaneously or in quick succession. These scenarios lead to increased risks and greater challenges for communities and ecosystems. During the Climate Conversation Series, two distinguished speakers from the University of British Columbia (UBC) presented their research findings on the complex relationships between different types of compound hazards. They discussed how overlapping events—such as floods occurring along with heat waves or wildfires following drought—can worsen the impacts of climate change and strain resources. Their presentations offered valuable insights into how these compound hazards affect disaster preparedness and response, as well as potential strategies for mitigation and adaptation in the affected areas.
Kaushal Gnyawali, a PhD candidate, is researching the compounding effects of post-wildfire flow hazards in British Columbia. He highlighted that the impacts of post-wildfire debris flows—such as property loss, damage to power lines, destruction of roads and highways, and disruption of livelihoods—are significant and can devastate multiple aspects of life. Gnyawali emphasized that these risks are often underestimated, leading to unforeseen hazards following wildfires. Even a small trigger, like an hour of light rainfall, can cause water to rush through channels, carving steep gullies and forming fast debris flows in burned watersheds. He also noted that such events can occur multiple times in concentrated areas over a short period. Gnyawali explained that wildfires destroy tree cover and ground litter, reducing water infiltration and exposing mineral soil. This leads to rilling, soil mobilization on slopes, and increased debris, ultimately triggering debris flows. He proposed two approaches to mitigation: reactive and proactive. Reactive mitigation involves interventions like digging ditches to divert debris flow. However, he pointed out that, while this method has been implemented on several occasions, it is not a long-term solution due to the unpredictability of debris flows. In contrast, he suggested proactive mitigation measures, such as conducting a quick analysis of the watershed and designing small-scale, low-cost construction projects to direct debris away from culverts. These proactive steps can be built in a few days or weeks, but financial, regulatory, or logistical challenges can sometimes extend the process to several years. Despite this, they provide long-term protection for terrain and slopes, even after debris flow events."Gnyawali acknowledged the benefits of a proactive approach but noted challenges like conflicting interests, lengthy approvals, budget constraints and short post-fire construction windows before rainfall.
Dr. Adeniyi Asiyanbi, an Assistant Professor of Geography, discussed the application of theoretical thinking and social sciences to the issue of compounding hazards. He noted that landslides and flooding often occur after wildfires, creating a common pattern across many landscapes. This represents a typical example of compound hazards, which are exacerbated by climate change. Multiple hazards and their drivers lead to intensified and amplified impacts. Climate change interacts with these elements—modulators, drivers, and hazards—in various ways. Modulators operate on a continental scale (e.g., El Niño), while drivers function at a regional level (e.g., tropical cyclones), which then contribute to hazards—these are the more immediate causes of impact, like wildfires.
Dr. Asiyanbi also outlined the different ways hazards can be compounded, drawing insights from the conceptual literature:
1. Multivariate: Multiple drivers acting simultaneously can produce multiple hazards and their resulting impacts.
2. Spatially: Multiple hazards can occur across different geographic landscapes.
3. Temporally: Hazards may follow a temporal sequence, such as a mudslide occurring after flooding.
4. Preconditioned compound events: Specific local conditions may trigger multiple hazards.
Understanding compound hazards is crucial due to their amplified impact on people, especially at the community level. Dr. Asiyanbi emphasized that these hazards can be confounding and confusing for both communities and policymakers. Climate change also affects the frequency, intensity, and patterns of compounding hazards, while also potentially creating new compound hazards in areas where none existed before.
In the context of his research on wildfire security in Whistler, Dr. Asiyanbi highlighted that there has been a pattern of decreasing snow deposition on the Whistler mountains. He pointed to research by UBCO’s Dr Mike Pidwirny suggesting that by 2085, half of the winter precipitation on those mountains will fall as rain instead of snow. One implication of these projections is that the ski industry in Whistler may no longer be viable by 2050. But when combined with the fact that the average temperature in Whistler is expected to rise by 3oC in 2050 compared to the recent past, leading to drier conditions and potentially more extreme fire weather, there is greater potential for wildfires that increasingly climb up the mountains. Such fires will lead to decreased vegetation on the mountains. As vegetation diminishes, this will trigger a positive feedback loop which means faster snow melts, resulting in early spring floods and greater dryness in summer, which in turn increases the frequency of extreme fire weather days and potential post-fire floods. He also discussed how compounding hazards relate to only a part of disaster vulnerability, specifically hazard exposure. He drew attention to the other aspects of vulnerability, which are (social) sensitivity and adaptive capacity, and how the concept of "double exposure" becomes equally important, to integrate vulnerability to climate change-related events with exposure to socio-economic and political impacts of globalization. Dr. Asiyanbi underscored the importance of considering the compounding impact of both compounding hazards and double exposure, which together, create new patterns of winners and losers in disaster scenarios.
Both presenters emphasized the importance of understanding the risks associated with compounding hazards. They highlighted the need for individual responses where appropriate and effective but that such responses must be part of a robust collective and systemic response to compounding hazards. They also emphasized the need to include the contributions of scholars and scholarly work in education for youths, teens, and children. It is vital to approach compounding hazards with a robust response, particularly through interdisciplinary collaboration. Additionally, it is crucial to consider who suffers the most from these impacts, as vulnerability issues are escalating. The question of social justice must therefore be given greater attention.
Thank you to the Disaster Resilience Research Network for jointly presenting this series, and to all who came and shared expertise and questions.