A Review of Interacting Natural Hazards and Cascading Impacts in Scotland

Simmonds, Rebecca and White, Christopher J. and Douglas, John and Sauter, Christoph and Brett, Louise (2022) A Review of Interacting Natural Hazards and Cascading Impacts in Scotland. National Centre for Resilience, Glasgow.

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Abstract

Weather-driven interacting natural hazards (referred to as 'multi-hazards' or 'compound events') cause significant disruption and damage to environmental and human systems in Scotland every year. Commonly, natural hazards are considered individually; however, natural hazards often arise from a combination of contributing, interacting physical processes. Failure to consider the multiple causes and drivers behind an event and the associated cascading impacts can lead to an underestimation of risk. Due to our changing climate, it is expected that many weather-related hazards will increase in intensity, occur more widely and more often than before, thereby increasing exposure to emerging hazards. This report provides an overview for Scotland of the nascent research field of compound events and cascading impacts. It provides conclusions concerning how these events and impacts have and may affect Scotland with climate change in the coming decades. The literature review identified publications relating to compound events and cascading impacts, but highlighted a significant lack of Scottish multi-hazard studies. This gap in knowledge is despite strong evidence that interpreting Scottish natural hazards using the framework of compound events and cascading impacts would significantly improve our understanding of these hazards, and potentially lead to improved resilience. Natural hazards in Scotland were reassessed here using a recently proposed typology for compound events based on their characteristics. Events and publications were re-evaluated and re-categorised as one or more of the types: multivariate (combination of drivers); spatially compounding (hazards affecting multiple locations); preconditioned (enhancement/triggering from antecedent conditions); and temporally compounding (succession of hazards). From this, a portfolio of case studies was created, providing initial evidence on each type and their significant impacts in Scotland. The events include: the concurrence of hot and dry conditions in North European spring/summer 2018; UK flooding from rain on saturated soil in 2019/2020; debris flows from rain on saturated soils in 2015/2016; and successive UK droughts to floods in 2012. This storytelling approach helps elucidate the complexities of compound events. Finally, a narrative of compound hazard events in Scotland was presented based on literature, the case studies, climate projections and an initial analysis of near future (2031-2060) multi-hazard pairings. This highlighted potential cascading risks and impacts across sectors and the environment in a changing climate. The literature review exposed a significant gap in Scotland-focused multi-hazard research, even for those more commonly expected pairings of hazards like compound flooding. By revisiting notable, recent weather events in Scotland with a multi-hazard focus, evidence of vulnerability to types of compound hazards was elucidated. This showed how interactions between hazards cause impacts that cascade across human and natural environments in a complex, interconnected network. Many of our identified compound hazard risks correspond to the CCRA3 priority climate risks for UK adaptation. Climate change is projected to intensify and increase the occurrence of compound hazards across spatial and temporal scales. Combining climate projections, CCRA3 priority future risks and our initial multivariate pairing analysis with the information from our re-categorised multi-hazard case studies reinforces the need for a greater understanding of compound hazards and their cascading impacts to ensure resilience. To better understand multi-hazards in Scotland, we propose the following eight (non-prioritised) high-level recommendations: 1.Re-categorise and reconsider notable single hazards as compound events; 2.Conduct Scotland-focused studies into the compound impacts of: hot and dry conditions, intense rainfall on saturated soil resulting in flooding and landslides, snowfall patterns resulting in changes to streamflows, winter windstorms, and wildfires; 3.Assess temporal sequencing across multiple compound event types; 4.Undertake research to better understand the drivers of compound events; 5.Improve the understanding of multi-sectoral cascading impacts and risks; 6.Assess indicative thresholds and feedback loops for critical infrastructure; 7.Apply storyline approaches to different adaptation and resilience scenarios; and 8.Develop a holistic, multi-sectoral impact-based multi-hazard approach.

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