Risk of compound flooding substantially increases in the future Mekong River delta

• Published in: Natural hazards and earth system sciences Vol. 24; no. 10; pp. 3627 - 3649
• Main Authors: Wood, Melissa, Haigh, Ivan D, Le, Quan Quan, Nguyen, Hung Nghia, Tran, Hoang Ba, Darby, Stephen E, Marsh, Robert, Skliris, Nikolaos, Hirschi, Joël J.-M
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 24.10.2024; Copernicus Publications
• Subjects: Astronomical tides; Climate change; Coastal flooding; Coastal storms; Coastal zone; Cyclones; Damage detection; Deltas; Disasters; Environmental risk; Fatalities; Flood control; Flood hazards; Flood management; Flood protection; Flooding; Floods; Geomorphology; Hurricanes; Population density; Rainfall; Rivers; Sailors; Storm surges; Storm tides; Storms; Tides; Tropical cyclones; Two dimensional analysis; Ho Chi Minh City Vietnam; Vietnam; Mekong River; United States > US
• ISSN: 1684-9981; 1561-8633; 1684-9981
• DOI: 10.5194/nhess-24-3627-2024

Floods are consistently identified as the most serious global natural hazard, causing devastating loss of life and economic damage that runs into multiple billions of US dollars each year. At the coastline, many flood disasters are in fact compound flood events, with two or more flood drivers occurring concurrently or in quick succession. In coastal regions the combined effect of fluvial (river) and coastal (storm tides – storm surges and high astronomical tides) floods has a greater impact than if each occurred separately. Deltas in south-east Asia are particularly exposed to coastal compound floods as they are low-lying, densely populated regions subject to the intense rainfall storm surges frequently associated with tropical cyclone (TC) activity. For our study we used a sophisticated 1D river model, combined with 2D storm tide levels, to analyse past–present and future compound flood hazard and exposure for the Mekong River delta, one of the most flood-vulnerable deltas in the world. We found that with compound flooding, a greater area of the delta will be inundated, and some parts will flood to greater flood depth. Central areas around An Giang and the Dong Thap provinces are particularly impacted in our plausible scenario, where a TC makes landfall near the mouth of one Mekong River distributary. In the future delta, the impact of compound flooding is potentially more significant, as the same compound flood scenario inundates a greater area relative to the present case and to greater depth in many locations, and floods last longer. Compound flooding therefore has clear implications for flood managers of the future delta, who will need to ensure that existing and future flood defences are to the right standard and in the right locations to offer effective protection against this future risk.