The Impact of Climate Change on Winter Storm Damage in Europe

Abstract

Windstorms induced by extratropical cyclones in winter (winter storms) are one of the most destructive weather phenomena impacting Europe, and lead to significant economical losses and fatalities. Changes in both the storm track and individual storms are expected as climate changes. Understanding future changes in winter storm activity is thus key for risk assessment and damage mitigation in Europe. This thesis combines state-of-the-art climatic projections from 29 General Circulation Models (GCMs) participating in the 6th phase of the Coupled Model Intercomparison Project (CMIP6), with the open-source weather and climate risk assessment model CLIMADA to obtain a set of relevant projections for future winter-storm-induced damages over Europe. More specifically, we study the uncertainties, spatial patterns, and atmospheric factors of influence of future projected windstorm damages occurring during the winter half-year (October-March: ONDJFM). We use an ANOVA model to partition the uncertainty in the projections of the damages into four different sources: the climate model, the stochastic, the emission scenario, and the impact function uncertainty. We find that the climate model uncertainty dominates the uncertainty in the projections of damages related to frequent events, but that the stochastic uncertainty dominates for damages related to extreme events, highlighting the need for improvements in climate models and an increased number of ensemble members. Spatial patterns of the future changes in winter storm damages projected by the multi-model ensemble show a median increase in the damages in a narrow band covering parts of the British Isles, northern mainland Europe, southern Scandinavia and the Baltic states, and a median decrease in the rest of the European domain, in agreement with an eastward extension of the North Atlantic storm track into Europe. The large variability in the projected changes of extreme surface winds between GCMs suggests that projected storm damages cannot be explained exclusively by the changes in the storm track. We investigate the changes in extreme loss events by combining the different climate models and model members resulting in two long simulations of 1920 years of modelled climate and find solid evidence for the intensity of rare and extreme events to increase more relatively to the intensity of more frequent events. We study the role of different remote climate drivers, such as the tropical warming, the arctic amplification, and the stratospheric polar vortex strength, as well as the trends of different indices of atmospheric circulation, such as the North Atlantic Oscillation (NAO) and the East Atlantic/Western Russia pattern (EAWR) on the projected wind extremes and associated losses. We find climate models projecting the strongest changes in the ONDJFM mean states of the NAO and EAWR indices to be associated with significantly different responses in terms of spatial patterns and changes in frequency and intensity of future winter storm damages. Also, we find polar amplification and changes in the strength of the stratospheric polar vortex to potentially influence the future extreme winds and damages over Europe. Our findings identify climate features that influence part of the variability in future European wind losses, with potential applications in the assessment of future climate simulations, or in seasonal forecasting of winter storm activity and damage. Our study also provides a common framework which can serve as a guidance for future climate risk assessment studies which could similarly take benefit of the association of a large ensemble of GCMs’ projections with a powerful open-source risk assessment model.