b. Mean state of heatwave metrics for the PRD
Heatwave metrics (HDF, HWD, and HWT) were calculated for the land area of the Pearl River Delta (PRD). The PRD experienced an average of 56 very hot days in the summer during the 2010s, and this number is projected to increase to over two months in the 2040s under different scenarios (Fig. 6). By the 2090s, the differences among scenarios become more pronounced. If a more aggressive GHG emission reduction scenario is adopted, the number of very hot days is expected to decrease by 9%, reaching 65 in the summer of the 2090s compared to the 2040s. Conversely, under SSP2-4.5 and SSP5-8.5 scenarios, the number of very hot days will continue to increase after the 2040s, by 25% and 60%, respectively.
On average, heatwave events lasted for six days during the 2010s. In the 2040s, mean HWD is expected to increase by two to three days in different scenarios, while the intensity is expected to increase by 0.2°C to 0.4°C. In the worst-case scenario in the 2090s, a heatwave event in the PRD could last for 23 days, which is three times longer than that in the 2010s, and the mean daily maximum temperature could reach 36°C.