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Drought and salinity intrusion in the Mekong Delta: What are the fundamental solutions?

Updated: 18 hours ago


Saltwater intrusion in the Mekong Delta will occur earlier, penetrate deeper, and become more extreme in the future, requiring solutions beyond the current temporary measures.


A man carrying a plastic bucket walks past a dried-up pond in Ben Tre province in March 2024. Photo: NHAC NGUYEN/AFP via Getty Images.


Is the situation still under control?


Regarded as Vietnam's "rice bowl", the Mekong Delta is facing increasing pressure from climate change and human exploitation activities, leading to increasingly severe salinization. This threatens not only agricultural productivity, especially rice cultivation and aquaculture, but also leaves millions of residents at risk of freshwater shortages for daily use.


The two most extreme drought and salinity intrusion events in the Mekong Delta in recent years were in 2016 and 2020. During the 2016 dry season, around 160,000 hectares of rice and vegetables were affected by saline intrusion deep into the interior fields. Saline water encroached on freshwater sources in rivers, causing around 800,000 people to experience severe freshwater shortages. The situation in 2020 was even more severe, with a 4g/l salinity level intruding about 60 km up the Tien River and 40-50 km along the Hau River, around 8-10 km deeper than in 2016. Along the Ham Luong River, the affected area stretched 78 km inland, 5 km further than the deepest 2016 level. During the 2020 dry season, drought and salinity intrusion seriously impacted 57,000 hectares of agricultural land and caused freshwater shortages for 40,000 households, mainly in Ben Tre and Ca Mau provinces.


This year's drought and salinity intrusion in the Mekong Delta came as no surprise, with temperatures ranging from 38°C-40°C. The causes were also predictable: in addition to long-standing water security imbalances due to the proliferation of reservoirs and hydroelectric dams in the upper Mekong River basin, compounded by the El Nino effect, the impacts of climate change have further exacerbated the situation. While the series of emergency declarations by provinces like Tien Giang, Long An, Ca Mau, and others regarding salinity intrusion and freshwater shortages may have caught many off guard, it does not mean these areas are helpless against this year's drought and salinity. These are the regions typically hit hardest during such periods, and the declarations should be understood as proactive warnings to allow provincial authorities to respond promptly to situations of household and agricultural water scarcity. Although this year's drought and salinity arrived earlier and penetrated deeper than the long-term average, both authorities and residents in these localities have some experience forecasting and coping with salinity intrusion. For instance, according to Dr. Huy Nguyen, an independent environmental and climate change consultant for several international organizations, a recent survey on April 25, 2024 showed that residents proactively left land fallow during the third crop season, limiting damage (around 1,000 hectares left uncultivated, with yield losses on about 5,000 hectares). Household water supply remained stable. The authorities also had temporary solutions to transport and sell affordable freshwater to particularly affected areas.


The Mekong Delta cannot continue to rely excessively on groundwater resources, which currently account for 90% of household water usage in the region, as these resources are suffering from severe depletion.

However, this does not mean that such coping mechanisms will remain effective in the future. The overall trend indicates increasingly extreme, earlier, deeper, and longer-lasting salinity intrusion events. The Mekong Delta cannot continue to rely heavily on groundwater, which currently accounts for 90% of household water use but is severely depleted. Moreover, Vietnam cannot unilaterally intervene in the issue of sharing water security along the Mekong River among countries. According to experts, the Cambodian government's plan to build the Funon Techo canal, drawing water from the Mekong River into the Gulf of Thailand, will deprive the Mekong Delta of freshwater, increase saltwater intrusion, and disrupt its ecosystem. While a detailed environmental impact assessment is needed to clarify the overall effects of this project, the two countries must discuss it, as constructing the canal will undoubtedly deprive the Mekong Delta of freshwater, making it increasingly difficult to mitigate salinity intrusion during the dry season.


Therefore, Vietnam still needs a more proactive and long-term solution for an increasingly difficult and uncertain future.


Global solutions to mitigate impacts of saltwater intrusion


Many coastal communities around the world also face saltwater intrusion issues and have implemented creative long-term solutions. One of the most common approaches is constructing prevention infrastructures such as sand dams, artificial sandbanks, or saltwater intrusion barriers in the US and Australia. These structures help keep saltwater away from residential and agricultural areas.


Additionally, countries situated below sea level or lacking freshwater resources, such as the Netherlands and Singapore, utilize desalination and groundwater recycling technologies. They have developed wastewater treatment and seawater desalination systems to convert saltwater into usable water for residential and industrial purposes. In Singapore, treated saltwater can even be consumed directly. These technologies not only provide clean water sources for communities but also reduce their dependence on freshwater resources vulnerable to saltwater intrusion, enhancing their resilience against climate change and other environmental issues.


However, it should be noted that these technologies require substantial construction and maintenance costs, typically only affordable for developed nations.


During the saline intrusion season, residents in many areas of the Mekong Delta even have to purchase clean water for daily use. Photo: NHAC NGUYEN/AFP via Getty Images.


Solutions to mitigate saltwater intrusion impacts in the Mekong Delta


Vietnam's situation is not yet as dire or freshwater-scarce as the aforementioned countries. Therefore, their costly infrastructures and technologies should remain peripheral concerns. The Mekong Delta still receives considerable rainfall, even with projected decreases due to global warming. The solutions Vietnam needs to focus on for proactively adapting to salinity intrusion are water resource coordination, enhancing forecasting capabilities, and maintaining existing saltwater intrusion prevention infrastructures. These solutions require interconnected and cohesive implementation across localities.


Optimal utilization and allocation of water resources in the Mekong Delta is paramount. This firstly involves programs and initiatives for efficient and sustainable water use, such as promoting water-saving irrigation methods, water reuse in agriculture and households to reduce reliance on natural freshwater sources, especially during the dry season. Rather than mere general calls, specific technologies for each region need to be implemented according to long-term plans with close online monitoring involving agencies from central to local levels and rapid inter-provincial coordination mechanisms. Additionally, the Mekong Delta's abundant rainwater resources must be leveraged. For instance, Ca Mau province receives an average annual rainfall of around 12 billion m3 across the entire province, nearly seven times the freshwater demand of its entire population. Therefore, efficiently harvesting rainwater (storing it during the rainy season for use in the dry season) can improve household water supply for many residents in areas particularly affected by saltwater intrusion. This can also reduce groundwater extraction, which is causing water depletion and land subsidence. Dr. Dang Hoa Vinh and colleagues have researched and proposed rainwater storage bags for Ca Mau province and piloted their application in some areas. These bags not only provide sufficient water for domestic use during the dry season but also replenish groundwater resources for agricultural production during the rainy season. The rainwater storage system consists of a rainwater catchment roof (including gutters and debris filters), a filtration unit, an untreated water storage tank, and a clean water storage tank for use. The storage tanks are constructed from concrete and connect to groundwater wells via pipes. These pipes "return" water to the groundwater wells when the rainwater storage tanks are full and draw groundwater when the tanks are empty. According to the researchers, a storage tank with a capacity of 7-9m3 can provide over 60% of the basic water needs for a 3-4 person household during the dry season (with the remaining 40% from groundwater).


Furthermore, water resource optimization includes "nature-based solutions" and crop restructuring. Nature-based solutions like creating freshwater reservoirs or expanding mangrove buffers along the coast can create brackish-freshwater transition zones and mitigate saltwater intrusion, while also providing suitable environments for different cropping systems adapted to varying salinity levels. To adapt to increasing salinization, it is necessary to delineate zones and classify livelihoods based on salt-tolerant agricultural practices in coastal areas. Additionally, farmers should be assisted in transitioning from salt-sensitive crops to more salt-tolerant varieties like certain rice and fruit trees, as well as integrated aquaculture.


Following the record 2016 salinity intrusion event, the Mekong Delta provinces implemented numerous programs to assist residents in coping with drought and salinity. However, these new solutions have only addressed temporary situations in a piecemeal fashion. The Mekong Delta requires large-scale programs to support residents in achieving self-sufficiency in freshwater supply for the dry season and enabling sustainable resource exploitation and utilization over the long term. The difficulty lies in the absence of an inter-provincial mechanism for evaluating and collaborating on the widespread implementation of effective solutions. Agricultural management in Vietnam also faces significant challenges as the majority of farmers operate on a small scale. Moreover, facilitating livelihood transitions among residents to adapt to salinity intrusion not only requires monitoring and oversight to ensure compliance with planning but also necessitates identifying markets for these alternative products.


Vietnam's current saltwater intrusion prevention infrastructure primarily comprises salinity control sluice gates and auxiliary structures that have been and are being constructed at the mouths of the Tien and Hau Rivers as well as the western sea mouths. Additionally, there is a system of embankment rings and salinity barrier dams to prevent the intrusion of seawater and water from major rivers into the interior regions. The operation and management of all these structures demand intelligent inter-provincial coordination aligned with accurate and effective salinity intrusion monitoring and forecasting systems. Simultaneously, frequent maintenance and upgrades are required with substantial funding; otherwise, the consequences will outweigh the benefits, leading to severe ecological imbalances in the future, particularly in the river mouth areas where saltwater and freshwater converge. However, at present, these infrastructures lack cohesive investment and management, instead being subject to the resource limitations and capabilities of individual provinces, thereby constraining their actual effectiveness. While large-scale systems are strictly monitored, smaller structures operate spontaneously. Notably, many minor structures have deteriorated and lost functionality.


Ultimately, all solutions are contingent upon forecasting capabilities. Forecasting requires the development of reliable computational models leveraging proactive monitoring technologies and techniques that utilize salinity data from multiple critical river locations to transmit information to national meteorological centers for alerts. A key weakness of Vietnam's current forecasting system is the lack of integration, outdated equipment, and piecemeal investment in monitoring stations and meteorological data centers, primarily reliant on funding from international cooperation programs. Furthermore, open data-sharing mechanisms for the scientific community have yet to be implemented for utilization in national priority forecasting projects, resulting in forecasts that are typically short-term, while medium- and long-term forecasts have limited accuracy. Therefore, the government needs to establish mechanisms and large-scale funding programs to enable scientists to participate in and develop strategic forecasting technologies.


References:




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