Sea level rise affecting the Vietnamese Mekong Delta: Water elevation in the flood season and implications for rice production

In this study, we assessed the impact of sea level rise, one of the most ascertained consequences of global climate change, for water levels in the Vietnamese Mekong Delta (VMD). We used a hydraulic model to compute water levels from August to November-when flooding is presently critical-under sea level rise scenarios of 20 cm (= Delta20) and 45 cm (= Delta45), respectively. The outputs show that the contour lines of water levels will be shifted up to 25 km (Delta20) and 50 km (Delta45) towards the sea due to higher sea levels. At the onset of the flood season ( August), the average increment in water levels in the Delta is 14.1 cm (Delta20) and 32.2 cm (Delta45), respectively. At the peak of the flood season ( October), high discharge from upstream attenuates the increment in water level, but average water level rise of 11.9 cm (Delta20) and 27.4 cm (Delta45), respectively, still imply a substantial aggravation of flooding problems in the VMD. GIS techniques were used to delineate areas with different levels of vulnerability, i.e., area with high (2.3 mio ha = 60% of the VMD), medium (0.6 mio ha = 15%) and low (1 mio ha = 25%) vulnerability due to sea level rise. Rice production will be affected through excessive flooding in the tidally inundated areas and longer flooding periods in the central part of the VMD. These adverse impacts could affect all three cropping seasons, Mua (main rainfed crop), Dong Xuan (Winter-Spring) and He Thu (Summer-Autumn) in the VMD unless preventive measures are taken.