Climate Adaptation Comes at a Cost for Vietnam’s Rice Basket

A rice – shrimp field showing a rice plot with peripheral ditches and dikes in the coastal area. (Courtesy: Dang Kieu Nhan)

In Southern Vietnam, where the Mekong River spreads and reaches like a hand into the East Sea, water is part of every aspect of local life. Shrimp grow in pools of brackish water among lush green forests. Fishermen wander the ocean in search of tuna. Even the air sits heavy and hot with humidity until the monsoons bring brief relief.

The water of the Mekong Delta also sustains hundreds of thousands of rice paddies. The region, known as Vietnam’s rice basket, accounts for half of the country’s overall rice production and around 17% of rice globally, including rice bound for New York City. But as sea levels rise, the marine contamination of agricultural lands, called saltwater intrusion, is threatening rice production in the delta. The country may soon have to decide what price it is willing to pay to retain its food security.

“Farmers are already doing everything they can to adapt. For them to do any more, it will require government investment,” said Daniel Osgood, a senior researcher at the Columbia Climate School. “But with investment, it comes down to where it can do the most good.”

A group of researchers recently assessed the cost of a process called land fallowing, leaving arable land unplanted for part of the growing cycle, that might help protect against the agricultural impacts of sea-level rise. Their work, published in the journal Science of the Total Environment, is the first to examine the relative cost and benefits of this strategy for farmers in Vietnam’s rice basket.

Fallowing even “one rice season in the upper part of the Mekong Delta can have substantial economic benefits,” said Dat Tran, a research scientist and economist at the Florida Legislative Office of Economic and Demographic Research and one of the study authors.

The delta is split into three distinct growing regions, according to Dang Kieu Nhan from the Mekong Delta Development Research Institute. Because of saltwater intrusion, the coastal areas have already transitioned to aquaculture, giving rise to a $10 billion industry. The middle region has both freshwater and saltwater seasons, and uses a system of sluice gates and irrigation to take advantage of both. During the wet season, when there is enough freshwater, farmers grow rice; in the dry season, they use seawater for aquaculture.

The uplands have largely escaped saltwater intrusion so far, and farmers there can still harvest three rice crops a year. But the delta is sinking due to groundwater loss, and soon, the upper delta will become vulnerable as saltwater penetrates further inland. Vietnam could potentially see sea-level rise as high as 8.7 inches in the coming years according to models from the Intergovernmental Panel on Climate Change.

Controlling salt-water intrusion through engineering across the delta could cost just over $10 billion, when adjusted for inflation, according to the new study. The team of seven researchers assessed how much an alternative strategy would cost. They looked at fallowing, a soil-revitalizing technique used by farmers the world over for millennia.

While the process has long been employed by Indigenous farming communities, it came to be seen as unsophisticated in the modern era. Regional governments considered it wasteful to leave productive land unplanted. Now this form of cyclical planting could offer much needed solutions for the Mekong Delta.

For a rice farmer in the upper delta, fallowing would mean planting fields in rotation, leaving a single field unplanted for one of the three growing seasons. Doing so would allow the soil to recover and retain more freshwater, effectively storing it for future use. Saturated fields could prevent salt water from intruding during the dry season and be used to control salt water intrusion in the lower regions of the delta.

“Fallowing could be enough to sustain the delta for the next 20 years if done on a large enough scale,” said Tran.

The cost to the government would be much lower than the engineering solutions. Tran and the team estimate that some 45,000 to 124,000 hectares (about 111,000 to 306,000 acres) would need to be fallowed annually to keep saltwater out. Land-fallowing could cost the government an estimated $47 million and $130 million a year, before even considering compensation for farmer’s lost production.

Farmers have focused on diversifying their crops in the lower levels of the delta. Because of the popularity of this strategy, it may be hard to convince upper delta farmers to participate in a fallowing program. “Farmers have no reason to fallow,” said Nhan.

However, according to Tran, fallowing, paired with engineering solutions, is likely to have greater benefits for the region in the long run.

“Regardless of what farmers would want to do,” Tran said, “freshwater availability year-round is always paramount for water supply, irrigation crops and fruit trees, and keeping saline concentration at a level where aquaculture can thrive.”