## 3 Experiments
### Storm Surge  
Storm surge is the most severe impact of tropical cyclones in river deltas. The combined consequences of high winds and water levels are responsible for considerable property damage and high causality rates in densely populated delta river regions worldwide [298; 375]. In total, 26 of 48 major coastal deltas are located in tropical areas (see Figure 5), making them vulnerable to cyclonic storms. The IBTrACS database (v04r00) (downloaded from the IBTrACS website [[https://www.ncdc.noaa.gov/ibtracts/index.php?name=ibtracts-data](https://www.ncdc.noaa.gov/ibtracts/index.php?name=ibtracts-data)]([https://www.ncdc.noaa.gov/ibtracts/index.php?name=ibtracts-data](https://www.ncdc.noaa.gov/ibtracts/index.php?name=ibtracts-data)); IBTrACS-All data v04r00 all storms points shapefile (accessed on 1 January 2021)), which contains complete global datasets of historical tropical cyclone tracks from 1842 to 2019, is used to calculate the density of all tropical cyclone tracks, shown in Figure 8. Many previous studies have documented a substantial global increase in severe cyclones and a consistent shift of the latitude of maximum tropical cyclone intensity, which agrees with the projections of future climate models [376]. Many studies have also assessed the potential risk of tropical cyclones in the coming decades and centuries in densely populated river delta cities/regions. Table 1 shows the risk rate index of 48 major coastal cities, and Table 2 summarizes the risk conditions of the world's most significant river delta regions. Figure 7: M\({}_{2}\) TACs in four different regions of the Indian Ocean: (**a**) the Arabian Sea, (**b**) the Bay of Bengal, (**c**) Africa, and (**d**) the Australian region. Symbols inside boxes indicate three different frequency bands: squares are the sub-annual (SA) band, circles are the annual (ANN) band, and stars are the interannual (IA) band. Station names are also indicated. Color shading of the symbols indicates positive (shades of red) and negative (shades of blue) TACs, according to the legend at the bottom right. Background colors show tidal amplitudes (corresponding to the color bar at the right of each subplot in units of meters) and phases (solid lines, in increments of 30\({}^{\circ}\)) from the TPXO 7.2 global solution [374]. The figure is taken from [372]. The work of [378] examined the spatio-temporal patterns and the return periods of tropical storms and hurricane landfalls along the East and Gulf Coasts of the United States by analyzing 105 years (1901-2005) of tropical cyclone strikes. A tropical hazard index (THI) was developed to estimate the vulnerability of these regions from a geographic perspective. The THI of the Mississippi River Delta has a value of approximately 130. The work of [379] analyzed tropical cyclones that affected the Yangtze River Delta and the Pearl River Delta from 1951 to 2010 and found that the frequency of tropical cyclones has varied harmonically, with periods ranging from 2 to 6 years. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Delta (Country)** & \
\begin{tabular}{l} **Risk Rate of Change Index 1** \\ **(Rank)** \\ \end{tabular} &
\begin{tabular}{l} **If the Delta Is in Tropical** \\ **Regions or Not** \\ \end{tabular} \\ \hline Krishna (India) & 0.28(1) & Yes \\ Ganges-Brahnaputra-Meghna (Bangladesh) & 0.22(2) & Yes \\ Brahmani (India) & 0.22(3) & Yes \\ Godavari (India) & 0.21(4) & Yes \\ Limpopo (Mozambique) & 0.21(5) & Yes \\ Sebou (Morocco) & 0.19(6) & No \\ Indus (Pakistan) & 0.19(7) & Yes \\ Shatt-el-Arab (Iraq) & 0.16(8) & No \\ Hong (Vietnam) & 0.16(9) & Yes \\ Mahanadi (India) & 0.16(10) & Yes \\ Irrawaddy (Myamar) & 0.15(11) & Yes \\ Senegal (Senegal/Mauritania) & 0.13(12) & Yes \\ Tana (Kenya) & 0.13(13) & No \\ Volta (Ghana) & 0.12(14) & No \\ Pearl (China) & 0.12(15) & Yes \\ Dnieper (Ukraine) & 0.11(16) & No \\ Yangtze (China) & 0.10(17) & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The world’s 48 major coastal deltas.