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SEA LEVEL RISE AFFECTING THE VIETNAMESE MEKONG DELTA: WATER ELEVATION IN THE FLOOD SEASON AND IMPLICATION FOR RICE PRODUCTION

Abstract. 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 (= 20) and 45 | SEA LEVEL RISE AFFECTING THE VIETNAMESE MEKONG DELTA WATER ELEVATION IN THE FLOOD SEASON AND IMPLICATIONS FOR RICE PRODUCTION REINER WASSMANN 1 5 NGUYEN XUAN HIEN2 CHU THAI HOANH3 5 and TO PHUC TUONG4 1 Institute for Meteorology and Climate Research IMK-IFU Forschungszentrum Karlsruhe Kreuzeckbahnstr 19 82467 Garmisch-Partenkirchen Germany E-mail reiner.wassmann@imk.fzk.de 2Sub-Institute for Water Resources Planning SIWRP Ho Chi Minh City Vietnam 3International Water Management Institute IWMI Colombo Sri Lanka 4International Rice Research Institute IRRI Los Baños Philippines 5 Formerly at IRRI. Abstract. 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 A20 and 45 cm A45 respectively. The outputs show that the contour lines of water levels will be shifted up to 25 km A20 and 50 km A45 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 A20 and 32.2 cm A45 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 A20 and 27.4 cm A45 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