c. Spatial analysis of heatwave metrics
The spatial patterns of the aforementioned heatwave metrics were plotted to illustrate future heatwave distribution in the PRD. Sea areas are masked out from the spatial plots to highlight the land information. All the analyses in this section are based on the SSP2-4.5 scenario, an intermediate scenario in which the social, economic, and technological trends do not change significantly from historical patterns.
In the 2010s, coastal areas had fewer very hot days than inland areas, and rural areas had fewer very hot days than urban areas. For the 122 days in the experiment period, only 9.9% of land area experienced more than 90 very hot days each summer in the 2010s. This value will increase to 41.2% and 63.9% of land in the 2040s and 2090s, respectively. In other words, in the 2090s, following the current trend, approximately 64% of the land area will suffer from high temperatures for over three months every summer, with 12% of the land area facing more than 110 very hot days, which is almost every summer day. Fig 7(a)–(c) indicate that the areas of Guangzhou, Foshan, Jiangmen, and Dongguan are at highest risk of extreme heat events, both currently and in the future due to their location farther from the coast, higher latitude, and increased urbanization. Climate change and the expansion of urban areas are projected to exacerbate this trend in the coming decades. Our results further show that urban grid cells surrounded by other urban grid cells experience higher 2 m temperatures (0.84 °C in the 2010s and 1.06 °C in the 2040s) than those surrounded by rural grid cells, with this effect expected to be more pronounced in the future due to continued urbanization. Fig. 7(d) and 7(e) show the differences in the HDFs between the 2040s and 2010s and those between the 2090s and 2010s. The greatest increase in the HDF corresponds to coastal areas in 2090s. This increase is not significant in the 2040s, which indicates that coastal areas will mostly become more vulnerable to such events at the end of the century.