Unveiling the cascading and non-synchronous time of emergence of change across the climate–hydrology–hydropower nexus

Climate change has intensified hydrometeorological uncertainties globally, threatening water reservoir functions that are vital for the sustainable development of society. However, the timing and cascading propagation of climate impacts through the climate–hydrology–reservoir operation nexus remains unresolved. In contrast to previous studies that primarily focus on the magnitude of future runoff changes, this research develops a nexus analysis framework to identify the Time of Emergence (ToE) across the entire water resource system. Using the Three Gorges Reservoir (TGR) as a case study, we integrated Coupled Model Intercomparison Project Phase 6 multi-scenario simulations with a machine learning-based reservoir operation model to quantify the sequential propagation of climate signals. The nonparametric Kolmogorov–Smirnov test was used to identify the ToE for climate, hydrological, and operational variables. The findings demonstrate a significant cascading effect: climate variables will deviate from natural variability in the early 2030s, followed by significant shifts in extreme runoff and reservoir operational benefits. While flood control pressure emerges as early as 2033, significant changes in water supply appear in 2035, and annual hydropower generation remains relatively stable without a clear ToE within the study period. This temporal divergence complicates the coordination between flood control, hydropower, and water supply, as existing operating rules based on historical stationarity may fail to balance these shifting goals. These results provide a critical temporal map for decision-makers, emphasizing the need for proactive and dynamic adaptive management strategies before operational benefits reach their respective thresholds of change.