Think global, act local: Fighting sea-level-rise in the Mekong Delta

Author: Pablo Acebillo- enCity’s Senior Associate, Planning + Transport

 

A recent study on sea-level-rise is going viral. Employing an alternative technique to measure the topographical elevation more accurately, Scott A. Kulp and Benjamin H. Strauss suggest that climate change consequences for coastal cities might be worse than we expected. Settlements lying on wetlands such as the Netherlands or the Mekong Delta in Vietnam might suffer severe floods in the coming decades..

They argue that the standard technique, the Shuttle Radar Topography Mission (SRTM), models the elevation of upper surfaces and not of bare earth terrain. In doing so, this technique incurs in large errors in a positive bias when used to represent terrain elevations. The authors propose a new technique based on the CoastalDEM, an improved version of the SRTM model using a neural network to perform nonlinear, nonparametric regression analysis of SRTM error. In essence, the new modelling technique reaches a higher level of accuracy when measuring the real terrain elevation, and thus is more suited and reliable to predict coastal areas which might suffer flood in the future.

The new simulation based on the model showed that all the estimates on sea-level rise for the coming century were far too optimistic. The new research shows that some 150 million people are now living on land that will be below the high-tide line by 2050. This is particularly worrisome for the Asian continent which concentrates the largest impact of population living on flood risk areas. Specifically, more than 70% of the people worldwide currently living on implicated land are in eight Asian countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, Philippines and Japan.

In the case of Vietnam, where enCity is working in some projects related to climate change resiliency, the research finds that about one-quarter of Vietnam’s population live in areas that will be inundated by midcentury. South Vietnam including the Mekong Delta and parts of Ho Chi Minh City could all but disappear. The previous method, shown in Figure 1 to the left, demonstrates the current expectations of submerged land by 2050. But the new outlook, the second map, indicates that the bottom part of the country will be underwater at high tide.

Figure 1_Adapted by Author based on: Lu, Denise and Flavelle, Cristopher (2019) ‘Rising Seas Will Erase More Cities by 205, New Research Shows’, The New York Times, 29 October.
Available at: Rising Seas Will Erase More Cities by 2050, New Research Shows
(Accessed: 30 October 2019)

enCity is determined to play a crucial role in delivering resilient solutions for such challenges. Figure 1 shows Ben Tre Province in dashed line, in which enCity is currently delivering the new strategic masterplan, with the environmental and coastal protection as one of its main strategic guidelines. As its visible from the map, Ben Tre is right on the spotlight of the potential damages in the Mekong Delta. The flood studies developed by enCity also show a considerable flood risk for the Province. Figure 2 shows the affected areas by 2025 and 2045. By the mid-century enCity forecast that over 80% of Ben Tre’s areas will be under at least 0.5m flood risk. Even being more optimistic than the recent research presented in this article, the reality strives for bold and decisive actions in the region. One of these actions drawn up by enCity include the provision of a dyke system to protect settlements from flood and agricultural fields from saline intrusion. This dyke system is integrated with the transport network, in order to both optimise the investment for socio-economic development as well as provide a secure evacuation route in case of severe flood episodes. Urban development will be concentrated in higher ground and clustered into larger towns to allow for better protection.

Other policy measures advocate for a more flexible agricultural land use. This would be more supportive while allow farmers to adapt their crops to changes in response to market and climate conditions. Since saline intrusion is already a serious issue affecting the local agriculture production, enCity also suggest to zone agricultural land based on water supply source (saltwater, freshwater and flexible zone) and downsize the area of freshwater crop to reduce resource consumption in the face of future supply shortages. These extreme weather conditions would also be smoothed through the preservation of the coastal mangrove forest along Ben Tre’s coast. Several research studies have shown how mangrove ecosystems help mitigate the energy carried by storm waves and thus reduce the flood risk inland.

Figure 2_Source: enCity, 2019.

Both the recent research results as well as the upcoming Ben Tre Strategic masterplan show how critical it is to take action now in order to tackle the effects of climate change in the future. As planners and policy makers, we need to stand up and contribute to make the built environment a more resilient and secure place for future generations to come.

Link to original scientific paper: https://www.nature.com/articles/s41467-019-12808-z