Sea-Level Rise and Land Subsidence: Impacts on Flood Projections for the Mekong Delta’s Largest City

Abstract

Abstract:The present paper demonstrates that inundation levels in the Mekong Delta's largest city, Can Tho, are predominantly determined by ocean tides, sea-level rise, and land subsidence. Our analysis of inundation patterns projects that the duration of inundation at an important road in the city will continue to rise from the current total of 72 inundated days per year to 270 days by 2030 and 365 days by 2050. This is attributed to the combined influence of sea-level rise and land subsidence, which causes relative water level rises at a rate of 22.3 mm·yr −1 . People in the Mekong Delta have traditionally lived with floods, and thus there is certain resilience among residents in coping with small floods. At present, daily maximum inundation depth, which is generally shallower than 10 cm on the road, seems to be still manageable; however, our analysis indicates that this will start drastically increasing in the coming decades and reach an average depth of 70 cm by 2050. Effective and well-planned actions to mitigate the effects of land subsidence and sea-level rise are urgently required, otherwise, local inhabitants will encounter an unmanageable increase in inundation depth and duration in the coming decades. This study, which considers both sea-level rise and land subsidence, suggests that inundation depth and duration are projected to rise much faster than those indicated by previous studies, which only consider sea-level rise.

Systèmes agraires et changement climatique au Sud

“…Entre terre et eaux, le delta du Mékong Avec 55 000 km², le delta du Mékong est un des mégadeltas asiatiques (figure 4.14) : 18 millions de personnes y vivent (330 habitants/km², 20 % de la population du Vietnam), notamment en cultivant 7,5 millions d'hectares de terres formées par les alluvions du fleuve accumulées depuis plus de 6 000 ans (Takagi et al, 2016). Bien que limitrophe de la mégapole de Ho Chi Minh Ville 17 , le delta du Mékong ne contribue qu'à moins de 10 % de la production industrielle du pays.…”

“…Avec un rabattement de l'aquifère pouvant atteindre 70 cm/an 29 , la subsidence induite en surface varie de 1,5 à 5 cm/an. Cet effet du changement global (Takagi et al, 2016) 30 vient s'ajouter à la transgression marine due à la dilatation ther mique de la Mer de Chine (changement climatique) à un rythme sept fois supérieur.…”

Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam

“…Average subsidence rates for the Mekong delta were determined at 6 mm yr −1 from 1987–2006 by surface water level trend analysis (Fujihara et al 2015), 17.1 mm yr −1 from 1993–2013 for Can Tho city ( Takagi et al 2016 ) and 16 mm yr −1 from 2006–2010 at 15 monitoring stations by InSAR (Interferometric Synthetic Aperture Radar) ( Erban et al 2014 ). For Ho Chi Minh City (HCMC) local extreme rates of 46 mm yr −1 ( Erban et al 2014 ), and 70 mm yr −1 ( Minh et al 2015 ) are reported.…”

Long-Term Design of Mangrove Landfills as an Effective Tide Attenuator under Relative Sea-Level Rise

“…Some small island communities in the Philippines were subjected to frequent coastal flooding due to a sudden land subsidence triggered by the Bohol earthquake in 2013 [13]. Intense groundwater use, as well as natural consolidation, accelerated the rate of the subsidence in the Chao Phraya Delta, Thailand, and the Mekong Delta, Vietnam, which reached 5-15 cm/year and 2 cm/year, respectively [14,15]. On the other hand, the sediment accretion in mangrove forests is relatively slow, with a rate of several mm/year [16,17].…”