PhD Thesis Presentation - Projecting Heatwaves and Extreme Precipitation in the Pearl River Delta through the End of the Twenty-First Century using Kilometer-Scale CMIP6-WRF Dynamical Downscaling

The Pearl River Delta (PRD), a densely populated subtropical region in southern China, is increasingly exposed to heatwaves and extreme precipitation under global warming. This thesis investigates future changes in these hazards through the end of the twenty-first century using kilometer-scale CMIP6-WRF dynamical downscaling.

The first study establishes an MPI-ESM-1-2-HR-driven downscaling framework to project future temperature-threshold heatwaves under SSP1-2.6, SSP2-4.5, and SSP5-8.5. Relative to the 2010s, summer daytime and nighttime temperatures increase substantially by the 2040s and 2090s, with the strongest warming under SSP5-8.5. Heatwaves become more frequent, intense, extensive, and persistent, and events that occurred once per decade in the 2010s recur much more frequently by the late century.

The second and third studies use bias-corrected CMIP6 multi-model ensemble forcing to examine humidity-related heat stress. The second study applies an Excess Heat Factor (EHF) framework based on Wet-Bulb Globe Temperature (WBGT), showing large increases in heatwave condition days, earlier seasonal onset, and longer heatwave duration under SSP2-4.5. The third study develops a dual EHF framework based on Heat Index (HI-EHF) and 2 m air temperature (T2-EHF), distinguishing HI-only, T2-only, and Hybrid heatwaves. By the 2090s, Hybrid events dominate PRD heatwave land grid days, reflecting the increasing co-occurrence of high temperature and humidity.

The fourth study examines hourly precipitation extremes under global warming levels from 1.5 °C to 4.0 °C. Convection-permitting simulations better reproduce observed extreme precipitation than coarser domains with parameterized convection. Return levels increase with warming, while cross-warming-level Clausius-Clapeyron scaling rates are generally close to 7%/K, although within-period apparent scaling can exceed this rate.

Together, these studies show that future climate extremes in the PRD are shaped by warming, humidity, moisture transport, urbanization, and convective processes, highlighting the value of high-resolution dynamical downscaling for regional risk assessment.