Event-based windstorm exposure in Sweden using observational and reanalysis-derived storm footprints.

Windstorm events are among the most damaging weather-related hazards in Europe, accounting for approximately 70% of the total insured losses. Existing research has primarily focused on storm climatology, hazard metrics, and loss-based assessments derived from insurance or damage data. While these approaches have advanced our understanding of windstorm dynamics and impacts, they provide limited insights into the spatial and quantitative characteristics of exposure.

Windstorm damage occurs where localised extreme wind gusts intersect with exposed socio-environmental assets. Exposure is therefore a central, yet still insufficient quantified, component of windstorm risk. In practice, exposure is often approximated through loss proxies or simplified indicators, largely due to persistent challenges in defining spatially coherent storm-affected areas from gust observations at the event scale.

This study develops an event-based windstorm exposure analysis for Sweden by linking observationally identified windstorm events with high-resolution national exposure datasets. Windstorms are identified from long-term station observations using local percentile exceedances combined with spatio-temporal clustering, resulting in a catalogue of extreme events. Storm-affected areas are identified using a single exceedance-based footprint approach applied to two wind data sources: interpolated station observations and ERA₅ reanalysis. In both cases, footprints are defined using locally derived percentile thresholds of wind gust intensity, capturing areas that experienced unusually strong winds relative to  local conditions.

For each event and footprint definition, exposure is quantified through the spatial intersection of extreme winds with datasets that describe population distribution, buildings, transportation, forest structure, and topography. Exposure metrics include population counts, infrastructure length, building numbers, and forest area.

A comparative analysis of exposure estimates across different footprint methodologies is conducted to assess the sensitivity of windstorm exposure to footprint definition. The resulting dataset provides an event-based representation of windstorm exposure in Sweden and establishes a foundation for improved attribution of impacts and future vulnerability and risk analyses.