The SEI Water, Coasts and Ocean team has long studied the compound and cascading effects of climate change on critical infrastructures and social vulnerability. These risks are often overlooked because different sectors tend to focus on monitoring their own fields without assessing how disruptions in other sectors might affect them or how they, in turn, may impact other areas of society.

Within the CrisAct and HydroHazards projects, SEI researchers Karina Barquet, Matilda Gunnarsson, Jung-Ching Kan and Marlon Passos have analysed how Sweden is managing the effects of droughts, floods and heatwaves. Their findings reveal key lessons that should inform decision-making at both the local and national levels in Sweden. Many of these insights may also be relevant for other countries.

Which risks are increasing in Sweden?

One of the most significant consequences of a warming climate is changes to the water cycle, which can result in both prolonged dry spells and more intense flooding. The researchers have identified hydroclimatic hazard hotspots across Sweden. Heatwaves have intensified in the south, while the risk of flooding has increased in both southern and northern regions. Overall, Sweden has become warmer and wetter.

These changes have major consequences for critical infrastructure and essential societal functions, including electricity supply, drinking water, wastewater treatment and roads. The SEI team is also studying the impact of these supply shocks on human systems, particularly in relation to food security and public health.

The challenge of interconnected climate hazards

Climate hazards rarely occur in isolation. Instead, they often interact in ways that amplify their effects. These are known as “compounding hazards” and “cascading risks”, both of which pose serious challenges to managing climate impacts effectively.

Compounding hazards involve multiple threats occurring together or in sequence. They can be categorized into three different types:

• Temporally compounding hazards occur at the same time, such as a drought and a heatwave, which together can exacerbate crop losses.
• Spatially compounding hazards happen in the same spatial area within a short period but not necessarily simultaneously, such as when a storm triggers a river flood.
• Preconditioned events occur when prior conditions worsen the effects of a hazard, like dry soil failing to absorb excess water, leading to intensified runoff or landslides after heavy rainfall – as recently observed in Norway.

The term “compounding events” can refer to any of these scenarios.

In parallel, cascading effects occur when an initial disruption triggers a chain reaction of failures across interconnected systems. For example, flooding could disable an electricity station, causing substation failures and widespread power outages. This, in turn, could disrupt essential services such as hospitals, schools and traffic lights. Given the complexity of modern infrastructure, these ripple effects can escalate quickly, affecting entire communities.

Understanding and predicting climate hazards

To improve the prediction of both single and compound hazards, SEI researchers are experimenting with machine learning approaches. They are testing various methodologies that structure data across time series, multiple features and spatial dimensions. This approach could enable much earlier predictions than are currently possible, providing valuable time to take preventable measures. However, developing a functional tool for this purpose would require more data and funding than is currently available.

Implications for Sweden’s infrastructure and services

In a recent study, SEI researchers analysed the concurrence of heatwaves and droughts in Sweden. They observed a pattern of intensification during the summer months, especially in the southern province of Skåne (Scania) and around Stockholm. These trends can have significant consequences, such as crop losses and water shortages, which may affect hydropower production and lead to increased electricity prices.

Managing these risks requires understanding of how interconnected systems react to disruptions. SEI researchers are therefore studying cascading effects within service and infrastructure networks.

Together with the municipality of Halmstad, the team has developed a framework to model multi-sectoral interdependencies. This model helps water associations and electricity providers understand how their systems interact with others and how disruptions might propagate. By integrating stakeholder input, the team can identify vulnerable services and pinpoint critical infrastructure where breakdowns would have the most severe consequences.

This information allows planners and decision-makers to prioritize investments and develop appropriate contingency plans. It is essential to assess the importance of each component within the broader system and determine where redundancy measures – such as back-up services or alternative infrastructure – are most necessary.

Such studies add nuance to climate adaptation strategies by highlighting the most critical functions, making adaptation efforts more targeted. For example, when modeling the cascading impacts of urban flooding, the team found that just 1.3% of critical infrastructure nodes were particularly disruptive. Protecting key assets – such as power plants, storage tanks and wastewater facilities – could significantly reduce overall risk.

For security reasons, the project applies network analysis to open-source data, which makes the findings less precise but also minimizes sensitivity concerns.

Key lessons

Climate change requires a fundamental shift in how we plan our societies and prepare for extreme events. Based on SEI research, five key lessons emerge:

• Prepare for cascading risks. Understanding how disruptions in one sector can propagate through interconnected systems is essential.
• Prioritize critical nodes. Infrastructure components that provide a majority of a service, such as an electricity hub supplying 70% of a neighbourhood’s power, must be protected.
• Address social inequality. Climate change impacts will exacerbate existing inequalities and may create new vulnerabilities.
• Assess nature-based solutions. Many risks can be significantly reduced through nature-based solutions. However, municipalities often struggle to compare their cost effectiveness against conventional “grey” solutions.
• Use the right solution for the right problem. No single approach can address all challenges. In flood-prone areas, adaptation strategies should focus on integrating nature-based solutions, establishing designated flood zones, and protecting critical infrastructure. Local redundancies should be created to minimize cascading risks, while public awareness and information campaigns can enhance resilience and improve spatial planning for future developments.