Coastal Cities Are at Highest Risk of Damaging Floods. The study lists the 10 most vulnerable cities when measured as percentage of GDP as: 1) Guangzhou; 2) New Orleans; 3) Guayaquil, Ecuador; 4) Ho Chi Minh City; 5) Abidjan; 6) Zhanjing; 7) Mumbai; 8) Khulna, Bangladesh; 9) Palembang, Indonesia; and 10) Shenzen.