Seasonal predictability of compounded variable renewable energy droughts in Europe using the German Climate Forecast System

Variable Renewable Energy (VRE) droughts — prolonged periods of low renewable energy availability — pose a significant threat to the stability and resilience of Europe energy grid, as renewable energy sources expand to meet climate targets. While the climatology and synoptic drivers of these events are well-documented, their seasonal predictability remains largely unexplored. This thesis assesses the German Climate Forecast System (GCFS) version 2.2 prediction skill for compounded wind and solar VRE droughts across Europe. We develop novel operational indices for solar, wind and compounded energy production, from surface solar radiation and wind speed, weighted by national energy capacities. Validation of the compounded index against documented events confirms its utility in identifying real-world energy shortfalls. This research bridges a critical gap in VRE drought predictability, despite the current lack of model bias correction and sensitivity tests on drought thresholds. Future work should resolve these limitations and explore ensemble subsampling and advanced statistical methods that leverage teleconnection patterns like the North Atlantic Oscillation (NAO) to enhance predictive skill. Our analysis reveals that the GCFS’s skill in predicting the local frequency of VRE droughts is spatially heterogeneous. Furthermore, the predictability of compounded droughts is not a direct function of its individual components, revealing complex, non-additive dynamics. However, we demonstrate that the model provides significant and reliable skill in forecasting the spatial extent of droughts when aggregated over larger regions. Anomaly correlation coefficients (ACC) reach 0.59 for Central Europe and 0.65 for Southern Europe. This research confirms the potential of operational seasonal forecasting models to provide actionable prediction skill on large-scale VRE droughts, which is crucial for strategic energy planning, grid management and risk mitigation.