Floods in Mekong Delta Under Sea-Level Rise Projections By IPCC AR5

Abstract:

One of the mightiest rivers in the planet, the Mekong ranks 10th amongst the world’s great rivers on the basis of mean annual flow at the mouth. It flows southwards over a distance of approximately 4,800 km from its source to the sea, through six different countries: China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam. This great basin has been considered to be one of the most sensitive areas in the world to climate change.

The present paper investigates fluvial flood hazards in urban areas in the Mekong Delta to inundation due to seasonal flooding, a phenomenon which is likely to be exacerbated by future sea-level rise. Unlike past researches which mainly focus on flooding due to river discharge from upstream or heavy precipitation, the present paper scrutinizes the influence of ocean tides. The research reveals that ocean tides predominantly determine water elevation even in an upstream location such as Can Tho City, 80 km inland from the river mouth, and that the river flow causes tidal damping and effectively reduces the energy of the incoming tides. This tidal damping is especially pronounced during the rainy season. Analysis based on the water levels monitored by the Mekong River Commission reveals that the ground near the riverbank of Can Tho had experienced inundation for a total of 215 hours between July 2009 and June 2010 (2.5% of the time over a one year period). It is also shown that inundation reached up to a maximum height of 47 cm above the roads of Can Tho downtown in this one-year period.

Assuming two scenarios of sea-level rise of 25 cm in the middle of the 21st century and 60 cm in the end of the century, all based on the Fifth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR5) projections, it was found that the duration of inundation will be prolonged from the present percentage of 2.5% to 7.5% and 24% of the year, respectively.

It is important to note that while at present this flooding is seasonal and limited, in the future it could become more frequent and persistent, even without considering the more extreme SLR scenarios outlined in the IPCC AR5.