2.1. Historical Events and Flood Protection of Shanghai
Shanghai has witnessed frequent extreme flooding induced by TCs. 148 TCs affected the region from 1949 to 2015 (Wang et al., 2017), among which 19 and 72 TCs generated storm surges of higher than 1.2 and 0.8 m, respectively. The annual maximum water levels (Fig. S1) were generally caused by the high tides and storm surges. For example, the arrival of Typhoon Winnie’s peak surge (2.35 m) coincided with the high astronomical tide, resulting in the highest storm tide (5.99 m) on record in Shanghai. In response to rising record levels, a flood defense system (floodwall along Huangpu River and seawall along the coast) was initiated in 1950s and has been reinforced since then (Fig. S1). Each update of protection standard is triggered by an extreme TC flood event (i.e., typhoons in 1962, 1974, 1981 and 1997), which heavily inundated the city (Xian et al., 2018). At present, Shanghai is protected by 480-km high level (1000-years) floodwalls and 508-km high standard seawalls which are designed to withstand a 100/200-year storm tides plus waves induced by 11/12-force winds (Saffir-Simpson Hurricane Category 1). In addition, rainfalls and river discharges are regulated by storm sewer drainage network and the dams/barriers/sluice gates, in order to prevent the compounding effects of pluvial, fluvial and coastal flooding (Yin et al, 2015; Xian et al, 2018).