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.

翻译：法国海上风电产业的快速发展要求对气候变化驱动下不断演变的海洋环境中的结构耐久性进行重新评估。依赖环境条件平稳性假设的传统设计方法已不再适用。本研究引入了一种新颖的统计框架，通过将非平稳广义极值（GEV）模型应用于月度极大值，来评估有效波高的未来变化。该方法旨在减少不确定性，并提供适应未来非平稳条件的稳健设计工具。基于CMIP6气候模型和再分析数据，结果显示在未来情景（SSP1-2.6和SSP5-8.5）下，法国大西洋和英吉利海峡沿岸预计将呈现更显著的季节对比趋势；而法国地中海区域由于极端值增长较弱及较大的不确定性（模型间差异），结果较难解释。预测表明冬季将更剧烈、夏季更平静，同时伴随季节性周期的偏移。总体而言，多模型集合表明极端海况的设计水平将有所提高。研究最终提出了一种计算结构运行寿命期内等效设计水平的新方法。该工具对于确保未来海上风电场在变化气候下的韧性和经济可行性至关重要。