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.