d. Return period analysis
Fig. 12 shows the return years in each scenario in the 2040s and 2090s relative to the once-in-a-decade event in the 2010s. The areas marked with dots and slashes correspond to return years of 0–1 and 1–2, respectively. In the 2040s, the areas with the highest extreme heat event reoccurrence are located in Guangzhou and Foshan. In the SSP1-2.6 scenario (Fig. 12 (a), (b)), the areas with return years of 0–1 and 1–2 in the 2090s is smaller than that in the 2040s. In addition, in the 2090s, Dongguan may not break the extreme temperature records corresponding to the 2010s. The spatial pattern of the return years in the SSP2-4.5 scenario is more favorable than that in SSP1-2.6 in the 2040s: the dotted and slashed areas are smaller, and more regions do not surpass the records set in the 2010s. However, in the 2090s, most locations in the PRD will suffer from the highest extreme temperature of the 2010s at least once every year or every two years. This situation is worsened in the SSP5-8.5 scenario in the 2090s, with almost every grid cell in the PRD having return year values of less than one year (Fig. 12 (f)).