Return levels of extreme European windstorms, their dependency on the NAO, and potential future risks

Abstract. Windstorms are the most damaging natural hazard across western Europe. Risk modellers are limited by the observational data record to only ∼60 years of comprehensive reanalysis data that is dominated by considerable inter-annual variability. This makes estimating return periods of rare events difficult and sensitive to choice of historical period used. This study proposes a novel statistical method for estimating wind gusts across Europe based on observed windstorm footprints from the WISC project. Estimates of the 10-year and 200-year return levels are provided. The North Atlantic Oscillation (NAO) is particularly important for modulating lower return levels and setting the tail location parameter, with a less detectable influence on rarer extremes and the tail scale parameter. The optimal length of historical data required to make an accurate return level estimation is quantified using both observed and simulated timeseries of the historical NAO. For estimating 200-year return levels, a data catalogue of at least 20 years is required. For lower return levels the NAO has a stronger influence on estimated return levels and so there is more variability in estimates. Using recent estimates of plausible future NAO states, return levels are largely outside the historical uncertainty, indicating significant increases in risk potential from windstorms in the next 100 years. Our method presents a framework for assessing high return period losses across a range of hazards without the additional complexities of a full catastrophe model.