A numerical hydraulic model was developed and used to investigate the spread of salinity intrusion and the propagation of flooding in the Vietnamese Mekong Delta under two proposed scenarios: "baseline" (2000s) and "future" (2090s). The baseline scenario was based on observed hydrological and salinity intrusion data from 1998 to 2006. The changes in upstream flow discharge in the future scenario (increased for most of the year) were derived from previous research results obtained using the Japan Meteorological Agency atmospheric general circulation model output for the IPCC SRES A1B scenario. The sea level rise in the A1B scenario (a projected 53-cm increase) was also included in the future scenario. The resulting salinity intrusion and flood water levels were then used to roughly estimate possible rice cropping durations. We found that large adverse changes in duration of rice cultivation in the future scenario were caused mainly by floods with greater peaks, larger areal extents, and longer durations. The area potentially suitable for growing triple rice crops decreased from 31% of the total delta area currently to 5%, whereas that potentially suitable for a single rice crop increased from 21% currently to 62%. Using GIS techniques, we divided the delta into three areas with different levels of rice vulnerability levels. Areas of high and medium vulnerability covered approximately 31 and 36% of the total delta area, respectively.
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