Climate change impact on flood hazard, vulnerability and risk of the Long Xuyen Quadrangle in the Mekong Delta

The Vietnamese Mekong Delta (VMD) has an important role in terms of food security and socio-economic development of the region; however, it is one of many areas of the world vulnerable to floods resulting from sea level rise (SLR) due to climate change. Therefore, management of flooding is a priority at national and regional levels in Vietnam. The Long Xuyen Quadrangle is the most important region in the VMD in terms of agriculture and economy. In the present work, flood hazard, vulnerability and risk were assessed and mapped to identify the priority areas in the Long Xuyen Quadrangle for flood mitigation. A hydrodynamic model was used to simulate the flood event of 2000 when a flood of 20-year return period occurred and caused loss of human lives and extensive damage. The calibrated model was then used to simulate a possible flood event in 2050 due to SLR. The resulting flood depth of the simulation was used to prepare inundation maps and to analyse flood hazard in this region, as well. The flood vulnerability of the region was assessed using the coastal areas flood vulnerability index (FVI) method. The FVI was determined by district, and flood vulnerability maps were developed based on these data. The results indicate that the major part of the study area (35.4%) can be classified as being at high risk. It was also found that 32.7% of the area is under medium risk and only about 18.4% is under very low and low risk; 10.2% of the total area is not subjected to flood risk. We show that district level flood vulnerability maps are potentially useful for decision makers and the public in planning better measures for adaptation and mitigation of the negative impacts of flooding.