Quantifying Carbon Leakage from Renewable Shortfalls in China's Power System under Future Scenarios

China's rapid deployment of wind and solar power is pivotal to its decarbonization strategy, but the pronounced temporal and spatial variabilities of these resources create recurrent shortfalls that necessitate fossil backup and lead to additional CO₂ emissions. We define this "carbon leakage" as the surplus emissions from dispatchable generation during wind-solar deficits, quantified using a high-resolution province-day framework for China across four climate-socioeconomic pathways to 2050. Results indicate substantial leakage across all scenarios, ranging from 100 to 140 MtCO₂, equivalent to about 4% of China's 2020 power-sector emissions. Renewable power deficits remain concentrated in central and eastern load centers, whereas the associated carbon leakage is more spatially dispersed and extends into major electricity-exporting regions. The drivers of leakage also shift seasonally. Power load remains the dominant year-round driver, while the seasonal drivers of leakage shift from temperature-driven demand in winter and summer to wind and solar variability in spring and autumn. These results indicate that managing renewable shortfalls is essential not only for maintaining reliability but also for avoiding structurally embedded rebound emissions during deep power-sector decarbonization.