Impacts of climate change on Dunkelflaute events and high residual load in Japan

Periods characterized by simultaneous low solar and wind power generation, known as "energy droughts" or “ Dunkelflaute,” pose a substantial risk to electricity supply in systems with high penetration of variable renewable energy (VRE). However, the influence of future climate change on the frequency, persistence, and system-level impacts of Dunkelflaute and high-residual-load events remains poorly understood, creating a critical knowledge gap for renewable-dominated power systems. In this study, we evaluated the impact of climate change on the occurrence of Dunkelflaute events in Japan using the large ensemble climate dataset, d4PDF. Machine learning techniques were utilized to analyze climate projection data, enabling the projection of future VRE generation and electricity demand under present and future +2 K/+4 K warming scenarios over approximately 1,000 years. The projections indicate reductions in both wind and solar power generation in Japan. Our analysis reveals a tendency for an increased frequency of Dunkelflaute events under future climate warming. Furthermore, electricity demand is projected to rise with increasing temperatures, indicating the potential emergence of unprecedented, long-duration high-residual-load events. These effects are expected to intensify with future shifts in power generation portfolios, particularly with further expansion of VRE deployment, and may alter the seasonal and meteorological drivers of high-residual-load risk in Japan. These findings underscore the importance of integrating climate change impacts into power system design to maintain energy supply stability under future conditions in the context of the ongoing energy transition.