More prolonged hot, dry, and compound dry‒hot events in China than expected based on observation-constrained projections

Despite growing evidence of intensifying hot and dry extremes, future projections remain highly uncertain due to substantial inter-model discrepancies, particularly at regional scales. This study investigates changes in the frequency and longest duration of hot, dry, and compound dry‒hot events across China and its ten major river basins using observational datasets and simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Results reveal widespread increases in the frequency and duration of hot and compound events, whereas increases in dry events are mainly concentrated in the Northwest, Yellow River, and Songhua River basins. Leveraging inter-model correlations between historical trends (1961–2014) and future changes (2031–2060, 2071–2100) under the shared socioeconomic pathways (SSP1-2.6, SSP2-4.5 and SSP5-8.5), we refine projections using a hierarchical emergent constraint (EC) framework. Constrained results indicate substantially higher frequencies and longer durations than previously estimated for most basins, except for event duration in the Southeast and Pearl River basins and hot-event frequency in the Songhua basin. Nationally, constrained projections indicate increases of 14.5–20.3 d in event frequency and 2.6–3.6 d in duration across the three scenarios during 2031–2060 and 2071–2100, relative to 1961–1990. The Southwest basin emerges as a hotspot, experiencing the largest increases. This study provides more accurate information for future changes in extreme events, which is encouraging to enhance regional climate risk evaluation and inform adaptation policy development.