🤖 AI Summary
This study addresses the inadequacy of conventional extreme-event design methods—based on stationarity assumptions—in ensuring the durability of offshore wind structures in France under nonstationary sea conditions driven by climate change. To overcome this limitation, a nonstationary generalized extreme value (GEV) model is developed, integrating CMIP6 multi-model ensemble projections with reanalysis data to quantify future changes in extreme sea states using monthly maxima of significant wave height. The work further introduces a lifetime-equivalent design sea state framework for forward-looking structural design. Results indicate intensified winter extremes and attenuated summer extremes in the Atlantic and English Channel, leading to heightened seasonal contrasts, while trends in the Mediterranean remain uncertain. Overall, design conditions are projected to become more severe, underscoring the necessity of abandoning stationarity assumptions to enhance climate resilience in offshore wind infrastructure.
📝 Abstract
The rapid expansion of the French offshore wind sector requires a critical reassessment of structural durability in the face of evolving marine conditions driven by climate change. Traditional design methodologies, which rely on the assumption of stationary environmental conditions, are no longer adequate. This study introduces a novel statistical framework to assess future changes in significant wave height by employing non-stationary Generalized Extreme Value (GEV) models applied to monthly maxima. This approach aims to reduce uncertainty and provide robust design tools adapted to the non-stationary conditions of the future. Based on CMIP6 climate models and reanalysis data, results reveal a projected trend towards a more pronounced seasonal contrast along the French Atlantic and English Channel coasts under future scenarios (SSP1-2.6 and SSP5-8.5), whereas the French Mediterranean Sea exhibits results that are more difficult to interpret, due to a weaker increase of extremes and large uncertainties (inter-model spread). Projections indicate more intense winters and calmer summers, along with a shift in the seasonal cycle. Overall, the multi-model ensemble suggests an increase in the design levels for extreme sea states. The research concludes by defining a new methodology for calculating an equivalent design level over the structure's operational lifespan. This tool is deemed essential for ensuring the resilience and economic viability of future offshore wind farms in a changing climate.