A living reality of climate change with its many consequences in the Mekong Delta is manifest in our lives. However, Vietnam's studies on sea level rise in prestigious international scientific journals are almost absent due to lack of data.

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Subsidence rate of the Mekong Delta region (Minderhoud et al., 2017).

“Go around” for collecting input data

Regarding the studies on the Mekong Delta, two articles assessing the risks from the causes of tides and sea level rise published in October 2019 in Nature Communication about the risk of rising sea levels in the Mekong Delta caused public stir, not only to Vietnamese researchers but also to many people who are concerned about the fate of their own lands. The first was by Minderhoud and colleagues at Utrecht University, The Netherlands. The second article by Kulp and Strauss is working at Climate Central Center, USA. The salient feature of these articles compared to previous studies focused on improving DEM maps and comparing sea levels under future climate change scenarios to assess the impact.

The question is how do international researchers get the data? In fact, both of these studies must "go around" to get research data about Vietnam. In the paper of the Dutch author, their input can be seen based on the interpolation of TOPO DEM data obtained from a 1: 200,000 scale map of the National Center for Water Planning and Investigation. of Vietnam. Meanwhile, its base map is derived from the Department of Maps with ground resolution of 0.5 km x 0.5 km, and an accurate height of 0.1-0.5m. For comparison, this map is then compared to two other DEM maps, SRTM and its improved version, MERIT. In the article of the US author group, the data set used is Coastal DEM, which they developed and developed themselves. This is an improvement of the SRTM map by using neural networks with input parameters including non-high parameter parameters such as population, vegetation cover, etc. The ground resolution of the map is limited to 1 km x 1 km. These are considered the best public and public DEM maps for the Mekong Delta.

Vietnam's main coordinating agency, the Ministry of Natural Resources and Environment, published two reports on climate change and sea level rise in 2009 and 2016. The data in these reports in particular, and the Climate and sea level rise data are generally not publicly available or difficult to access, even for local researchers. This goes against the trend of sharing scientific data that international scientists often do. Therefore, the introduction of public data hubs on climate change and sea level rise is essential.

As can be seen, the quality of the conclusions of these two articles depends entirely on the quality of the base map used. Maybe we have many other types of maps that have better resolution and error, like from the Department of Maps or other facilities, but because they are not widely shared, it is difficult to accurately assess them. To date, the two maps used to assess flood risk have been the best maps to help assess the risk of sea level rise.

Obviously, any of the above studies also has some limitations. For example, with the DEM map in the first article of the Dutch authors, there are some factors of accuracy that need to be further assessed. In addition, the fact that riverside and canals always have embankments with a certain height. With a map with a resolution of 500 meters x 500 meters or 1 km x 1 km, these studies did not model the impact of the dyke (the width is only 1-10% of this resolution). In order to do that, other analysis is needed with a more accurate DEM map with the appropriate flow model - factors that are outside the scope of the article, and in fact are very expensive, a feat. research deployment.

Although there are still some qualitative limitations or have not considered all the causes, the analysis in these two articles is conducted carefully and specifically, with publicly available data for control, thereby increasing dependence. The fact that foreign scientists can use our data to conduct good research is a good experience that can be learned. Although the data needs to be good enough, abundant and accurate enough in the research, making use of available sources is also an immediate way for us to solve the difficulty of input data to get the best results. good father.

"Looking at others and then back at me"

As a result, the risk of rising sea levels and current events will provoke many ideas for Vietnamese scientists to study more about rising sea levels in the Mekong Delta and its impacts. But in fact, most of the research done by local experts in this field has been published in prestigious international scientific journals. In contrast, foreign scientists have actively published very well assessments of the rising sea level of the Mekong Delta. This reflects the fact that we are lacking or not interested in gathering good scientific experts in the field of sea level rise to lead domestic research. Having good experts both helps us take the initiative in conducting research, and helps in better policy advice.

The lack of Vietnamese research is due to the second reason, the lack of sharing of scientific data. In fact, Vietnam's main coordinating agency, the Ministry of Natural Resources and Environment, has published two reports on climate change and sea level rise in 2009 and 2016. These two reports have assessed relatively full of risk and impact aspects of climate change and sea level rise with Vietnam. However, the data in these reports in particular, and data on climate and sea level rise in general are hardly public or difficult to access, even for domestic researchers. This goes against the trend of sharing scientific data that international scientists often do. Therefore, the establishment of data sharing centers (data hubs) publicly about climate change and sea level rise is very necessary.

The third reason is that our investment in building quality data is still very thin. In the field of sea level rise, we have, but we still lack a lot of important data on land, water levels, satellite images to help improve the content of studies. For example, we are not really interested in adopting quality long-term land displacement (VLM) measurements, or as investing in high-quality remote sensing observations and analysis to built the DEM (Digitital Elevation Model) map data sets well enough. Topographic digital maps are often combined from multiple survey data sources with sophisticated equipment and good processing algorithms. This map, if made and made public (in part or in whole), will be an important element for other studies as well as a basis for land planning and policy development.

The fourth reason is that the process of selecting and distributing research topics is not based entirely on scientific quality. The quality here should be measured by products published in good international journals, rather than into thick, stacked reports. Spending part of the topic to invite international experts to learn and improve the quality. For example, the Government of Singapore has spent a considerable part of paying for some leading international experts to participate in some stages of the project through cooperation, and on the other hand, actively inviting experts. Reputable read reviews report on Singapore's climate change and sea level rise. Taking high professional requirements makes the scientific content and results of the project become reliable, effectively serve Singapore in seaport planning, land encroachment and climate change adaptation.

Therefore, in the long term, in order to have policies to cope well with climate change and sea level rise, the first step is to have high-quality and reliable studies, which are only possible if We have built a good scientific team, allocated research resources through a transparent mechanism measured by the quality of international publications and encouraged effective domestic and foreign cooperation to research. The good news is that in recent years we have had more openness in our research data, for example, publicizing data from 5 tidal stations on the Rise Level Database (PSMSL Permanent Service for Mean). Sea Level). However, we may have to do very quickly in building good teams, data transparency, investing in background data and selecting research topics according to quality, because the risk of sea level rise threatens to flood. The Mekong Delta is near and not waiting for us.

Mekong Delta: What are the risks due to sea level rise?

The Mekong Delta is mainly alluvial soil that has been accumulated over thousands of years. In estuarine areas in general, alluvial soil and sand are porous, often flooded with soft ground, prone to subsidence or gradual sinking. Add to that the phenomenon of groundwater extraction, causing the soil to lose a buffer layer, so it is compressed (land compaction). In the Mekong Delta region, some measurements and modeling (Figure 1) show that HCMC has subsided 1 meter (!) Over a 25-year period (1991-2016). Other areas of the Mekong Delta such as Can Tho, An Giang, Soc Trang, Bac Lieu and Tra Vinh, the average settlement rate is about 1-1.5 millimeters per year. The rapid rate of subsidence of HCMC relative to other localities may be related to groundwater extraction and overall urbanization. In addition, the resonance effects of rising sea levels are also due to depletion of river water. This depletion can be caused by drought due to climate change, climate, or human causes, including overuse of water for agriculture and the construction of hydroelectric dams. In the Mekong Delta, the human factor has a greater impact, as countries in the upper reaches of the river (China, Laos) have been building a lot of hydroelectric dams. Consequently, there is no water in the downstream of Cuu Long. This will lead to the risk of seawater more easily entering the mainland, because there is no fresh water source to eliminate this salt water.

In addition, higher sea level rise coupled with the lack of fresh water will also exacerbate saline water intrusion, causing damage to rice cultivation, agriculture and people's livelihoods. The formation of dams along the Mekong River (central and upper Mekong) not only depletes the water source, but also leads to a serious shortage of sediment accumulation. This amount of sediment can in fact help improve the Mekong Delta's soil base and limit the impact of erosion and saline intrusion. According to a study, with the worst case scenario when the dams were built as planned, then the Mekong Delta would only receive 4% of the sediment compared to the original.

* Author: TS, Melbourne, Australia.

The author would like to thank Mr. Duc Hiep for the discussion to improve the quality of the article.

Refer

Kulp, S.A., Strauss, B.H. (2019) New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications, 10, 4844, doi: 10.1038 / s41467-019-12808-z

Minderhoud, P. S. J., Erkens, G., Pham, V. H., Bui, V. T., Erban, L., Kooi, H., & Stouthamer, E. (2017). Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam. Environmental Research Letters, 12 (6), 064006. doi: 10.1088 / 1748-9326 / aa7146

Minderhoud, P.S.J., Coumou, L., Erkens, G. et al. (2019) Mekong delta much lower than previously assumed in sea-level rise impact assessments. Nature Communications 10, 3847, doi: 10.1038 / s41467-019-11602-1

Source: Tia sang