1. How do you assess the current situation of drought and saltwater intrusion in the Mekong Delta? Compared to 4 years ago (2016), is there any difference between drought and saltwater intrusion in 2016 and this year?

Drought and saltwater intrusion in the Mekong Delta (MD) often occur in years with extreme climates and weather. Evidently, some dry seasons have a severe degree of drought and saltwater intrusion, which greatly affect the production and life of the Mekong Delta such as 1977-1978, 1997-1998, 2015-2016 and now 2019-2020, both due to extreme climate and weather. Analysis of the meteorological data series from 1975 to present, shows that the time, intensity and frequency of climate-weather extremes' activities in Vietnam in particular and Southeast Asia in general (including the Mekong River basin) tends to increase significantly. Therefore, the extent of drough and saltwater intrusion in the Mekong Delta is also increasing in terms of time, space, intensity, frequency, along with economic and environmental damages caused by them.

Saltwater in the rivers this year until now is basically equal and a little higher than in 2016. However, this year's damage (as of early March) is much lower than damage during 2015-2016 drought and saltwater intrusion. For example, the Winter and Winter-spring rice (2019-2020) with losses of over 30% is only 39,000 ha, accounting for 1.2% of the total cultivated area and 9.6% compared to the damaged area in 2015-2016. The number of households lacking clean water was over 95,000 compared to 210,000 households in 2016. This result is thanks to the adaptive initiative of the people in the South, besides the effective use of some irrigation works (including promoting the early completion of some saltwater intrusion control sluices), an important factor is the close guidance of MARD and provinces in the Mekong Delta from providing early warning information to adjusting the planting schedule, even limiting late rice areas to avoid saltwater intrusion, etc. 

2. What are the causes of drought and saltwater intrusion in the Mekong Delta at present?

It can be said that the main reason for causing drought-saltwater intrusion in the Mekong Delta is in the years with extreme climatic and weather conditions; the stronger the intensity, the longer the time will last, the more the extreme space will expand, the greater the economic and environmental damage. Apart from the orthodox cause, there are other supporting factors that contribute to drought and saltwater intrusion in the Mekong Delta such as the impact of upstream, changes in the basin surface environment, the increase water usage in production and life, etc.

In summary: There are many causes, but the main causes include: (1) The amount of water entering the Mekong Delta in the last months of the rainy season in 2019 and the first months of 2020 is lower than yearly average; (2) The rainfall in the last months of the rainy season in 2019 is also lower than yearly average, affecting the balance between saltwater and fresh water, which tends to move inland (an indispensable rule); (3) The subjective reason is that agricultural production has not changed significantly, so the amount of water used is still large, putting pressure on water source.

3. What do you think about drought and saltwater intrusion situation in the Mekong Delta in the future? In your opinion, what are the best solutions for the Mekong Delta?

At present, the hydrometeorology and irrigation industry has sufficient human, material and intellectual resources (network of monitoring stations, monitoring machines, scientific staff, international cooperation, forecast methods,etc.) to ensure good flood/drought/saltwater intrusion prediction in the Mekong Delta. The tropical monsoon climate of Asia has determined the law of the dry-exhausted season in the northeast monsoon (December to April of the following year), the rainy season in the southwest monsoon (May to November) takes place on the Mekong Delta every year. During the dry season, the combination of drought and saltwater intrusion often have the strongest impact on production and life in the period from February 15 to the end of April 15 (depending on each year). Therefore, in the past two months, how will the Mekong Delta prevent radical drought and saltwarter intrusion in case of extreme weather-climate combined with other side effects?

First of all, it is necessary to exchange long-term and permanent crop, plants and animal structure under the motto of saving water, using less water, suitable in all three regions of the Mekong Delta. To mobilize the movement of the entire population to fight against drought and saltwater intrusion in the Mekong Delta with reasonable water storage methods such as small reservoirs, tanks, ponds and swamps near houses or in villages and communes. The key provinces in the Mekong Delta can work with the Can Tho Water Supply Corporation, which can supply clean water in large quantities by pipeline leading to central drought and saltwater intrusion affected areas in the West. From these central points, water tank trucks are used to transport water to community groups. In the long run, if it works, the Government should formulate a strategic expansion project mentioned above that is capable of participating in preventing drought and extreme saltwater intrusion in key provinces in the Mekong Delta.

It is nescessary to build a system of sluices controlling saltwater and fresh water, suitable for both the output and the input on the system of canals, tributaries, dead-end rivers, etc., turning their conduits into a system of "mobile" reservoirs, “according to the time and rhythm of each tide ”, to trap the tide, control saltwarer  and store fresh water. This system only works during the peak of the dry season mentioned above, while in the rainy season, all control sluice gates are opened to let both output and input back to normal.

Large-scale water reservoirs should not be dug in the Mekong Delta, because the Northern and Central Lakes build up water in high areas and then build canals to drought-saltwater intrusion areas. The Mekong Delta is low, flat, acid sulphate soil. If digging a super-large lake with the elevation under - (3-4m) to store water, water will evaporate, seep longitudinally and transverse in accordance with the law of gradual exhaustion of system flow. The Mekong Delta's land bank is not extravagant because there is a dense system of rivers and canals, geology of the Mekong Delta is a thick layer of sediments that will make the lake water salty, acidic and accumulate toxins of production and life.

Regarding the specific forecast for 2020, the trend of saltwater / freshwater boundaries entering deeper into the mainland will continue in March but this situation may decrease in April. Comparing the saltwater intrusion situation in 2016 and 2020, it is found that "non-structural" solutions are particularly effective, so it is necessary to once again consider the "nature-based development" in the spirit of the Government's Resolution 120 / NQ-CP in 2017, which is very important.

MARD, together with the provinces, should boldly review the planning of irrigation systems to adjust in the direction of "taking advantage of nature" rather than "overcoming nature". Projects that were right in the past but no longer suitable for the new approach need to be modified or canceled if necessary. Rice areas with high water demand must be balanced.

It is nescessary to monitor the evolution of the water source at the end of the rainy season (from September and October) every year to have a plan to produce and store fresh water. In the long term, to serve people’s production and living, there should be a plan to build a fresh water system from An Giang - Dong Thap to supply water plants in the saltwater intrusion areas.

Management of groundwater extraction and exploitation currently needs improvement. Saltwater should be truly a resource rather than a risk, and the term "saltwater intrusion control" should also be used in a deliberate manner as an equitable treatment of salt water. Saltwater needs to be turned into practical action, even saltwater shrimp farming, depending on the period of growth, still needs freshwater to dilute to reach the appropriate salinity. Fresh water is still the most valuable resource for both living and production.
Economic sectors based on saltwater (or alternating saltwater/freshwater) are creating more opportunities for people. The Government gives priority to assisting people first of all in terms of water resources for domestic use, and at the same time supports the development of livelihoods that enable people to participate in the value chain fairly and effectively.

Dr. To Van Truong, March 19, 2020