3.3. SLR impact on flooding
Yin et al. (2020) provided the probabilistic SLR projections for
Shanghai, which take into account both climatic and non-climatic
(subsidence) components, under three Representative Concentration
Pathways (RCP 2.6, 4.5 and 8.5) by the end of 21stcentury, relative to the baseline year of 2010. The median (50th
percentile) estimates under RCP 8.5 are used here to investigate the
effect of local relative SLR on typhoon-induced coastal flooding and
inundation. We find that the projected SLR would lead to non-linear
impact on flood and inundation hazards. For example, the 3000-year flood
level at the Jinshan station (at the height of the seawall to cause
inundation) would become a less than 1000- and 900-year flood events in
the mid- and end-of-twenty-first century, respectively (Fig. 2). Overall
in Shanghai, compared with the current situation, typhoon-induced flood
inundation would occur two times more frequently with a 0.5-m SLR by
2050 and 20 times more frequently with a 1.36-m SLR by 2100.
Inundation severity will also significantly increase. Fig. 3d-i display
the derived coastal flood inundations for the three worst-cases under
the 2050 and 2100 sea levels. A cross comparison between Fig. 3a-c and
Fig. 3d-i reveals that extreme typhoon-induced coastal inundations in
Shanghai, as expected, would increase significantly under SLR. Although
the general patterns of inundation are characterized by a certain degree
of consistency between the current and 2050 scenarios, the flooded areas
are projected to increase by 26%, 24%, and 437% for Typhoon A, B and
C, respectively. Meanwhile, the projected SLR of 0.5 m could contribute
to a 23%, 19% and 74% rises in the average inundation depth for the
three cases, respectively. If the local sea level is raised by 1.36 m by
the end of the century, the predicted inundation areas for Typhoon A, B,
and C will be respectively 60%, 110% and 1360% larger than those with
the present-day sea level, and the average inundation depth will
increase respectively by 69%, 16% and 141%. Extreme flood hazards
caused by Typhoon A and B would almost totally inundate the Chongming
and Hengsha islands by 2100. Without an upgraded flood defense, Baoshan
and the coastal districts along Hangzhou Bay could also be greatly
affected by Typhoon A and C under the 2100 SLR.