Storing Mekong floodwater for an El Nino-hit dry season in 2027

This will depend on rainfall across the Mekong basin, water stored in Tonle Sap, upstream reservoir operations and dry-season flows. 

But the WMO's latest El Nino warning is a reason to prepare for a potential water shortage in the Mekong Delta during the 2027 dry season.

Giving farmland back its role as a water reservoir

Against that backdrop, Mekong floodwaters are still flowing into the delta and have risen rapidly in recent days. This raises a key question: Can more of the available freshwater be stored now to prepare for what could be a harsh coming dry season?

The Long Xuyen Quadrangle and Dong Thap Muoi have long served as two important natural flood-storage areas in the Mekong Delta. 

In the past, Mekong floodwaters would spread across these vast low-lying areas, remain on the fields for months and then gradually recede. 

The process not only brought sediment and fishery resources, but also slowed the flow and retained large amounts of water in the landscape.

The development of extensive flood-control dike systems has allowed many areas to produce three rice crops a year. 

At the same time, however, hundreds of thousands of hectares of farmland have gradually been cut off from their natural role in storing floodwater.

During a strong El Nino year, it may be time to reconsider that trade-off. Should some third-season rice fields be left unplanted to create more space for floodwater and freshwater storage ahead of the 2027 dry season?

Some areas are already taking steps in that direction. An Giang Province has plans to allow nearly 42,000 hectares of farmland to receive floodwater in 2026, mainly in the Long Xuyen Quadrangle and west of the Hau River.

The potential scale is easy to see. One hectare covered by one meter of water can hold about 10,000 cubic meters. 

That means 50,000 hectares could hold around 500 million cubic meters, while 100,000 hectares could hold about 1 billion cubic meters. 

These are large enough volumes to deserve serious consideration.

To be clear, these figures represent maximum storage capacity at a given time, not the amount of water that would necessarily remain in February or March 2027. 

Water will be lost through evaporation and seepage, flow into canals and rivers, and some will need to be released for farming. The question is, how much water can we retain, and for how long.

Accepting lower rice output to store freshwater amid El Nino

Flooding farmland has long been used mainly to bring in sediment, wash fields, improve soil, reduce pests and diseases, and support livelihoods during the flood season. The water is usually drained afterward to prepare for the winter-spring rice crop. 

This year, however, there is another strategic goal: storing freshwater to reduce the risk of drought and saltwater intrusion during the 2027 dry season.

Instead of draining the fields as quickly as possible to make way for the next crop, farmers could deliberately keep water in areas where planting does not need to start early, or even skip the autumn-winter rice crop, including some winter-spring rice fields in certain areas. 

In short, the goal is to slow the loss of freshwater from the delta.

If part of the land planned for rice production were instead used for floodwater storage, rice output in 2026 would fall, and farmers would lose income from that crop. 

In a normal year, the value of the third rice crop may take priority. But in a strong El Nino year, it is worth comparing the lost rice income with the value of the water stored and the potential losses avoided to winter-spring rice, fruit orchards, household water supplies, river transport, and other economic activities, if drought and saltwater intrusion become severe.

This means weighing farm income against water security, rather than assuming that growing an additional rice crop is always the better choice.

In any case, reducing the number of rice crops per year is already an increasingly encouraged trend. 

Skipping the third rice crop does not mean farmers have to lose all income during that period. In recent years, various flood-season livelihood models have been introduced in upstream areas, showing that flooded farmland can still provide income for local communities.

Storing floodwater could benefit the wider Mekong Delta

This cannot be a decision made by the two provinces alone. 

If An Giang and Dong Thap reduce part of their rice-growing areas to store floodwater, the immediate costs will fall on those provinces and their farmers. But the benefits of managing and preserving freshwater could extend to many downstream areas.

The central government should coordinate a Mekong Delta-wide water storage plan, rather than leaving each province to make its own decision. 

The plan should identify areas suitable for water storage, how much water they can hold, how long it can be stored and how it could benefit dry-season water supplies. 

The operation of major irrigation infrastructure should also be coordinated with water storage on farmland.

The central government should also establish a mechanism to share the costs. If society needs farmers' fields to provide water-storage space for the entire region, farmers should not be expected to bear the full income loss from skipping a third rice crop.

In the short term, participating farmers could receive direct financial support. 

Over the longer term, authorities could consider a payment system for water-storage and regulation services, compensating farmers and local governments for providing storage space in proportion to the benefits they create for the wider region.

Save water while it is still abundant

With a 'super' El Nino likely to last into early 2027, the government should work with An Giang and Dong Thap to reserve more space in the upper delta for floodwater, even if that means cutting some rice-growing areas and output.

Not all stored water will last until the end of the dry season. But keeping it for one to three months can still boost soil moisture, replenish canals and improve water supplies as the dry season begins.

Freshwater is abundant now. The priority should be to keep it, not let it drain away and fight drought and saltwater intrusion later.

Not every area is suitable. An Giang and Dong Thap should review enclosed fields in the Long Xuyen Quadrangle, west of the Hau River, the upper Tien and Hau rivers, and Dong Thap Muoi. 

Priority should go to areas where the autumn-winter crop has not been planted or can be skipped at relatively low cost.

These areas could become large-scale pilot sites, with authorities measuring water inflows, outflows and how much remains after 30, 60 and 90 days. We have to know how much of the water stored in September will still be there in November, December and January.

If the approach works, storage areas could be expanded in future El Nino years or when severe drought and saltwater intrusion are forecast.