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3.4.5. Combined and cascading effects

Different extreme events and different types can combine, thereby aggravating the risks to the energy system. For example, both droughts and heat waves are projected to increase in southern Europe. The simultaneous occurrence of these hazards can limit energy supply and transmission in hot, water-scarce regions while increasing peak electricity demand. The combination of these effects may threaten stability of electricity supply, with potential knock-on effects on other sectors that depend on a stable electricity supply. Another dangerous combination of impacts is river flooding with a storm surge, which can multiply flooding risks in coastal regions, including for energy infrastructure.

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Extreme events can also affect two or more components of the energy system simultaneously. The risk of cascading impacts and system failure is particularly high in the case of power outages, because electric power is central to many other components of the energy system as well as to society-at-large. Box 3.3 provides two examples of cascading impacts from damages to transmission lines.

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Box 3.3 Examples of wide-spread power outages resulting from storm damage to transmission and distribution networks

A large power outage took place in Italy and Sweden in September 2003, affecting 56 million customers. The primary cause was a storm that had caused a tree to fall and break a set of electricity transmission lines in Switzerland. The resulting decrease in tension caused an almost immediate chain-reaction of power-plant shut-downs, with subsequent loss of electrical power throughout Italy (except Sardinia and some other smaller islands). Although electricity supply was restored within hours in some northern regions, the black-out lasted for almost 24 hours in some Sicilian municipalities.

The triggering event for this systemic failure could have been avoided by proper maintenance of transmission lines and the foliage surrounding transmission lines in Switzerland. Further analysis of the events highlighted that the network operator in Italy did not act fast enough to reduce the grid capacity being used for pumped storage, which could have eased the burden on transmission lines from increased electricity imports from France. This case highlights that assessing risks and vulnerabilities of a system, and following through on necessary maintenance measures is integral to preserving its function in times of stress. By taking stock of potential vulnerabilities to the energy system, the damage costs of €1.2 billion could have potentially been avoided (Böttcher, 2016; Johnson, 2008).

Storm Gudrun caused significant destruction in parts of northern Europe in January 2005. In Sweden, 30 000 km of distribution lines were damaged, leading to long-lasting power disruptions for around 730,000 customers. In urban areas with underground cabling, power was restored within a few hours, whereas rural areas witnessed outages for up to 20 days. The Swedish network operators reported their losses of around 250 million euros, but the overall costs of the power interruptions to society were estimated at 3 billion euros (Gündüz et al., 2017).

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