Fig. 9. (a), (b), (c) Spatial plot of mean summer daytime heatwave
temperature (HWT) in the 2010s, 2040s, and 2090s. (d), (e) Spatial plot
of the differences in the mean summer daytime heatwave temperature
between the 2040s and 2010s and those between the 2090s and 2010s. All
figures correspond to the SSP2-4.5 scenario.
The nighttime heatwave metrics were also evaluated because consecutive
hot nights may pose a more significant threat to human health than very
hot days. Lower temperatures at night typically allow people to recover
from the daytime heat, and the occurrence of hot nights can reduce this
effect, which may lead to excess death tolls (Kovats and Hajat 2008).
Moreover, if consecutive very hot days occur with consecutive hot
nights, the health impacts may be more severe than those associated with
solely consecutive hot days or consecutive hot nights (Thomas et al.
2020). Among the human population, females and the elderly are more
vulnerable to extremely hot weather (Wang et al. 2021). Fig. 10 displays
the spatial patterns of the number of very hot nights (HNF) across
different decades. In the 2010s (Fig. 10 (a)) rural areas had fewer than
10 very hot night. As urbanization continues to expand, more regions are
expected to experience more frequent hot nights in the future. The
spatial pattern of HNF difference (Fig. 10 (d)) highlights urbanization
as a contributor, with more rural grid cells becoming urbanized and hot
spots. For the PRD, the spatial mean difference in the HNF is 21.7 and
50.9 nights in the 2040s and 2090s, respectively, considerably larger
than the mean difference in the HDF (14.6 and 28.7 days in the 2040s and
2090s, respectively). This increase will make it challenging for people
to recover from the daytime heat at night. Compared with the spatial
pattern of the HDF increase, which is concentrated in coastal areas, the
HNF increase is more significant and spatially dispersed, covering most
of the land in the PRD.