Compound winter low-wind and cold events impacting the French electricity system: observed evolution and role of large-scale circulation

Abstract

To reach climate mitigation goals, the share of wind power in electricity production is set to increase substantially in France. In winter, low-wind days are challenging for the electricity system when compounded with cold days that are associated with peak electricity demand. The scope of this study is to characterize the evolution of compound low-wind and cold events in winter over the 1950–2022 period in France. Compound events are identified at the daily scale using a bottom-up approach based on two indices relevant to the French energy sector, derived from temperature and wind observations. The frequency of compound events shows high interannual variability, with some winters having no event and others having up to 13. Over the 1950–2022 period, the frequency of compound events decreased, which is likely due to a decrease in the frequency of cold days. Based on a k-means unsupervised classification technique, four weather types are identified, highlighting the diversity of synoptic situations that lead to the occurrence of compound events. The weather type associated with the highest frequency of compound events presents pronounced positive mean sea-level pressure anomalies over Iceland and negative anomalies west of Portugal, limiting the entrance of the westerlies and inducing a north-easterly flow that brings cold air over France and Europe generally. We further show that the atmospheric circulation and its internal variability likely play a role in the observed reduction in cold days, suggesting that this negative trend may not be entirely driven by anthropogenic forcings. However, it is more difficult to reach a conclusion on the role of the atmospheric circulation in the observed decrease in compound events.