The Pearl River Delta (PRD) in southern China is a densely populated subtropical region with hot and humid summers. Conventional heatwave definitions based solely on dry-bulb temperature often underestimate heat risk in humid climates, yet few studies apply humidity-sensitive and temperature-based indices within a unified event-based framework. Here, we apply the Excess Heat Factor based on the Heat Index (HI-EHF) and 2 m air temperature (T2-EHF) in parallel to distinguish three exclusive heatwave event types (HI-only, T2-only, and Hybrid) Using bias-corrected CMIP6 ensembles dynamically downscaled with WRF, we analyse heatwaves in the 2010s, 2040s, and 2090s. Heatwaves are defined as periods of at least three consecutive days when either HI-EHF or T2-EHF is positive. Results show event composition shifts toward the Hybrid type. Under fixed 2010s reference thresholds, Hybrid accounts for 98.6% of PRD heatwave land grid days in the 2090s, while HI-only and T2-only account for 0.8% and 0.6%, consistent with mean-state migration and HI nonlinearity. HI-only events are short, thermally moderate yet humid episodes, rooted in pre-moistened land conditions and sustained by marine inflow. T2-only events remain radiation-dominated, though their dryness weakens as background humidity increases toward the late century. Hybrid events become more frequent, longer, and more intense, clustering in increasingly hot and humid regimes characterized by elevated low-level moisture and strong insolation. These findings highlight the importance of incorporating humidity-sensitive metrics in humid subtropical regions, where a multidimensional perspective is critical for accurate risk assessment and adaptation strategies.
Zuo et al. (Fri,) studied this question.