Saltwater intrusion threatens to wipe durian, rambutan off Vietnam's Mekong Delta

"Saltwater is penetrating deeper, and durian and rambutan are among the fruit trees least tolerant to salinity in the Mekong Delta region," said Dao Phu Quoc, director of the Center for Sustainable Development and Biodiversity under the Vietnam National University, Ho Chi Minh City.

The delta is the largest fruit basket of Vietnam, with over 20,000 hectares of durian, mainly grown in Tien Giang Province, 8,061 hectares of rambutan, and nearly 23,500 hectares of grapefruit.

Over time, farmers have abandoned thousands of hectares of jackfruit and rice to switch to durian cultivation, rapidly increasing the area of this crop, Quoc told an international workshop on sustainable development of the Mekong sub-region organized by the HCMC University of Law on Friday.

Quoc said among the fruits currently cultivated in the region, durian has the lowest salinity tolerance, followed by rambutan, oranges, and grapefruits.

The salinity tolerance threshold for durian is about 0.64 parts per thousand, meaning each liter of water contains 0.64 grams of salt; and the threshold for rambutan is 1.28 parts per thousand.

The water at the river mouths has been contaminated with up to 4 parts per thousand of salt, meaning each liter of water contains up to 4 grams of salt, during the dry season in recent years.

Quoc noted that over the years, the extent of saltwater intrusion has increased and the contamination has become more severe.

In the rivers of Vam Co Dong and Vam Co Tay that flow through Long An Province, salinity intruded by up to 150 km from the river mouths, as recorded in 2020.

"Salinity is increasing and penetrating deeper. Soon durian, rambutan, citrus fruits, and many rice varieties will gradually disappear," said Quoc, pointing out that during saltwater intrusion events in the past few months, durian and rambutan plants have wilted and their productivity has decreased.

The central government and local authorities need to find timely adaptive solutions and change the crops to ensure the livelihoods of the people, he said.

He emphasized that saltwater intrusion is unavoidable, and hence, "we need to turn this challenge into an opportunity," adding that there are many economically valuable aquatic species suitable for brackish, mineral-rich environments, such as white-leg shrimp, tilapia, and some mollusks, which have high export values.

Regarding fruits, soursop has good salinity tolerance and is favored in the U.S. market, but it has not been a focus in Vietnam. There are also new rice varieties that can tolerate up to 12.5 parts per thousand of salinity, Quoc said.

Attending the workshop, Luu Thi Thanh Mau, CEO of HCMC-based Phuc Khang Corporation, which specializes in "developing greenified apartments and greensmart cities," reported that the company has had a pilot model for livelihood transition for residents in Hau Giang Province.

Through its own research, the company has identified a number of challenges faced by the Mekong region, which are market impact, lack of policies, climate change, labor shortage, limited capacity, high production costs, lack of investment, and impacts from other countries' activities in exploiting and using the Mekong River's water resources.

From the pilot model and the challenges faced by the residents, Mau believes that for sustainable development, there needs to be a shift from individual, small-scale farming and livestock to large-scale farms combined with high technology, aiming for clean agriculture.

Agricultural land should be used for both cultivation and livestock, and also researched for integration with ecotourism.

A farmer measures the salinity level of the water in a drainage system next to his durian farm in Ben Tre Province, March 2023. Photo by VnExpress/Hoang Nam

Quoc believes that besides changing crops and livestock, the government should consider technical and financial solutions, incentivizing businesses to participate in processing agricultural and aquatic products. For example, technical solutions must be integrated, including building barriers, narrowing river flows at the river mouths to retain freshwater and prevent seawater from entering during tides.

Additionally, the government should provide policies for residents to easily access loans for new livelihoods, accompanied by support packages for agricultural technique transfer or technical training before providing loan capital.

Businesses participating in processing agricultural and aquatic products should be offered investment incentives.

According to a study the Institute of Water Resources Science under the Ministry of Natural Resources and Environment, four sectors of rice, aquaculture, fruits, and vegetables of the Mekong Delta suffered damage of more than VND70 trillion (US$2.96 billion) annually from 2020-2023 due to salt intrusion.

The study highlighted that 29% of the damage affects the fruit sector, 27% impacts vegetables and flowers, and 14% pertains to rice cultivation. Aquaculture bears the brunt of the losses, accounting for 30% of the damage, approximately VND21 trillion.

In the past ten years, the Mekong Delta has experienced two major saltwater intrusion events.

The historic saltwater intrusion in 2016 affected 160,000 hectares of land, causing damage of more than VND5.5 trillion. Ten out of thirteen localities in the region had to declare natural disasters.

Four years later, a prolonged six-month saltwater intrusion forced six provinces in the region to declare emergency saltwater intrusion situations. More than 43,000 hectares of rice were damaged, and 80,000 households faced a shortage of water. The government had to spend VND530 billion to assist eight provinces in coping.