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A review of interacting natural hazards and cascading impacts in Scotland

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.

Date: June 2022

Authors: R. Simmonds, C.J. White, J. Douglas, C. Sauter, L. Brett

This study provided an overview for Scotland of the nascent research field of compound events and cascading impacts. Providing conclusions on how these events and impacts have and may affect Scotland with climate change in the future. The literature review identified publications relating to compound events and cascading impacts but highlighted a significant lack of Scottish multi-hazard studies. There is 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.

PROJECT SUMMARY

Background/Context
Natural hazards, such as droughts, floods and landslides are caused by a combination of weather and physical factors. For example, droughts are caused by a prolonged lack of rainfall but, when combined with hot weather, they can be exacerbated. On the other hand, too much rain can cause flooding because the soil is full of water, like a soaked sponge, and rain cannot be absorbed, leading to runoff. Rain falling onto soaked ground can also weaken the soil structure and trigger landslides (Figure 1).
Normally, natural hazards are dealt with as individual events (i.e. drought from lack of rainfall), ignoring the connections between the factors which cause a hazard and without thinking about the impacts down the line that the hazard can trigger (agricultural losses leading to loss of jobs and emigration). This underestimates the full risk to the natural and built environment and human systems. Hazards connected to the weather will become more intense, more frequent and affect a greater area with climate change. Scotland needs to understand and plan for these multiple, interacting natural hazards to be resilient now and in the coming decades. 

Scotland needs to build resilience to increasing risks of multiple, interacting natural hazards that are driven by the weather and climate, and which will be made worse by climate change in the near future. Understanding how hazards are formed and how they impact the environment and society in different regions helps prioritise preparedness and adaptation. This study investigates the emerging topic of multiple, interacting hazards in Scotland. It collates global and national evidence, creates demonstrative Scotland-focused case studies on previous interacting hazards, indicates Scotland’s present and future vulnerabilities to interacting hazards and impacts and recommends where research is needed. 

The review we conducted shows there is a significant lack of Scotland-focused studies on multiple, interacting hazards, however, threats from these events do, and will increasingly, exist. To understand what types of interacting hazards and impacts affect Scotland, we collated information about multiple natural hazards from national and international studies that could be applicable in the Scottish context. Working backwards, we revisited notable Scottish hazard events to understand what combinations of factors caused them and their impacts. From this we created a portfolio of multiple, interacting hazard case studies that happened recently in Scotland.  

  • The first case study demonstrates how both hot and dry weather conditions caused the spring/summer drought which impacted water resources and agriculture across North Europe in 2018.
  • The second and third case studies show how successive periods of rain can cause flooding and landslides because of rain falling onto already rain-soaked soil. Widespread flooding experienced across Scotland in 2020/2021, and a landslide at the Rest and Be Thankful in Winter 2015/2016 highlight this interacting hazard process.
  • The final case study shows the dangers of a quick switch from dry to wet weather, as seen in the 2010/2012 drought to flooding events.

These case studies, in addition to global examples from the literature review, show how natural hazards need to be considered more widely. This is because natural hazards can be caused by multiple factors occurring at once in one area or spanning different locations; they can be triggered by previous conditions and they can happen sequentially, affecting the same location with successive problems, like a domino effect. Looking at how natural hazards are caused and connecting this with how notable Scottish natural hazard events took place, we have overcome the lack of Scottish focused studies and given an initial insight into what multiple, interacting hazards happen in Scotland. 

Flow diagram
Figure 1: Process of how rain on soaked soil can cause flooding and landslides [adapted from 1.]

Bringing this information together with climate change projections and our analysis, we show what multiple hazards Scotland may face in the next few decades and where might be most vulnerable. The whole of Scotland will become increasingly at risk to multiple, interacting hazards, with some areas experiencing hazards that are presently uncommon to them. Particular concerns include:

  • The combination of hot and dry weather conditions (often uncharacteristic for Scotland) leading to drought and environmental damage, but which could also help create the perfect conditions for wildfire hazards.
  • Warmer temperatures in winter are likely to reduce snow cover which could affect spring/summer streamflow from the lack of melted snow replenishing the water system.
  • There is uncertainty around the occurrence of winter storms which we need to understand better for Scotland, especially considering the succession of storms Scotland has experienced recently.
  • With projections of increased intensity and frequency of rainfall there is a greater risk from rain on rain-soaked soil leading to flooding and landslides.
  • Finally, there is a need to understand how different hazards follow each other. The projected increase in hot, dry periods interspersed with increasing rainfall highlight the need to be aware of flooding and droughts in close succession.

More research in these areas is needed to fully understand how Scotland will be affected.

This report aimed to provide a better understanding of Scotland’s vulnerability to the relatively new field of multiple, interacting weather-driven natural hazards and impacts. The information presented can guide Scotland’s resilience and adaptation priorities to interacting hazards in a changing climate.  

Three Key Points/Implications/Next Steps from Research
Research in Scotland is urgently needed to fill the evidence gap on multiple, interacting hazards  especially around hot and dry conditions, snow patterns and impacts on stream flow; wildfires; winter storms; flooding and landslides from rain on soaked soil; and the succession of hazards in one location. 
A better understanding is needed on how these multiple, interacting hazards can impact different sectors in Scotland and to identify thresholds and feedback loops for key infrastructure, e.g. transport network. 
The development of an impact-based approach that looks at multiple, interacting hazards from all angles is needed. Revisiting previous hazard events to establish their causes can fill the evidence gap and provide a clear, relatable narrative through case studies. Imagining what could happen in different interacting hazard scenarios, based on previous examples, could help prepare for future resilience. 

You can read the full report here

1. Bevacqua, E., et al. (2021). Guidelines for studying diverse types of compound weather and climate events, Earth’s Future. 9, (11). https://doi.org/10.1029/2021EF002340 

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