2025

Láng-Ritter, Ilona

Extratropical cyclones (mid-latitude cyclones) are important weather phenomena that often cause strong winds, heavy precipitation, and temperature changes as they move. While essential to the climate system, extratropical cyclones can develop into windstorms, which pose significant risks to society and critical infrastructure, such as electrical grids. The everyday functioning of modern societies depends on continuous electricity supply. With the current electrification of various sectors, the importance of reliable electricity supply continues to grow. Extreme and unexpected windstormrelated power outages can impact national energy strategies, highlighting the importance of effective risk assessment and mitigation. This thesis focuses on understanding the impacts of windstorms on Finland's electrical grid by exploring the meteorological and non-meteorological factors contributing to damage and assessing strategies to mitigate the impacts. The main findings highlight that wind gust speed and the spatial extent of strong wind gusts are the primary meteorological drivers of power outages, with damage rising exponentially when gusts exceed 20 m/s. Other windstorm characteristics, such as arrival and movement direction in relation to the country, further influence impacts. Windstorms with widely spread strong wind areas and tracks close by densely populated regions, such as those arriving in Finland from the northwest, cause widespread disruptions, while weaker but slower-moving windstorms, such as the ones arriving from the southeast, can accumulate localized damage due to prolonged gusts. Windstorms with low mean sea-level pressure (<980 hPa), particularly those arriving from the northwest, tend to be the most destructive. Soil frost significantly mitigates damage by anchoring trees to the ground, reducing power outages by up to 86%. The results show that both the presence of frozen soil and the depth of soil frost are important mitigating factors. Non-meteorological factors, such as forest characteristics, powerline infrastructure, and regional differences, also shape grid vulnerability and influence the overall impact of windstorms on electrical grids, making certain areas in Finland, such as Eastern Finland, more vulnerable than others. Seasonal and regional variations are notable: while winter windstorms are typically more intense meteorologically, summer windstorms can cause significant damage due to unfrozen soil and trees in full foliage. Machine learning and statistical models developed in this research enhance the ability to predict windstorm impacts, offering valuable tools for preparedness and mitigation. Selecting appropriate meteorological and non-meteorological parameters for impact assessment is essential to understand the complex interactions between hazard, exposure, and vulnerability factors. The analysis shows, for instance, that the number of power outages follows a power-law relationship with the tenth power of wind gust speed, identifying it as the most effective predictor for assessing power outages. The findings of this thesis support improved resilience strategies for Finland’s power networks, provide insights applicable to other densely forested regions with similar vulnerabilities, and contribute to a broader understanding of extratropical cyclone and windstorm impacts. Keskileveysasteiden matalapaineet ovat merkittäviä sääilmiöitä, tuoden usein mukanaan voimakkaita tuulia, runsaita sateita ja nopeita lämpötilan vaihteluita. Vaikka keskileveysasteiden matalapaineet ovat ilmaston kannalta hyvin tärkeitä, voivat ne myös kehittyä myrskyiksi, muodostaen merkittäviä riskejä yhteiskunnalle ja kriittiselle infrastruktuurille, kuten sähkönjakeluverkoille. Nykyyhteiskunnan toiminta perustuu jatkuvaan sähkön saatavuuteen. Eri sektoreiden sähköistymisen myötä, luotettavan sähkönjakelun merkitys on kasvanut entisestään.