The intensifying impacts of upstream dams on the Mekong

The Mekong Delta of Vietnam stands to be most in danger in the time of accelerating and intersecting impacts from climate change and hydropower. 

This year marked another record-setting dry season for the Mekong basin. Mekong Environment Forum, an NGO based in Can Tho City, has assisted the Mekong Dam Monitor project team in translating weekly updates on the operation of hydropower dams observed in the upstream Mekong over the last few years. We synthesized the updates in the first half of 2024 to map and provide insights into the updated impacts of dam operations on the downstream hydro- and eco-systems. 

The evidence supports our understanding on the likelihood of a double water crisis when upstream dams’ operations intersect with downstream climate change effects. These findings reaffirm recent experts and public concerns over the transboundary impacts of overinvestment in damming the Mekong. 

We call for cross-border collaboration and coordination to promote responsible, transparent, and sustainable use of the shared water resources in the Mekong basin. As a downstream victim, the Mekong Delta of Vietnam, like many Cambodian riverine communities and wetlands, stands to be most in danger in the time of accelerating climate change and hydropower impacts. 

Mapping the Updated Impacts of Upstream Hydropower Dams

From March to June 2024, the lower Mekong region – including northeast Thailand, Cambodia, Laos, and Vietnam – experienced high temperatures far exceeding expectations. Extreme dryness was observed in the Golden Triangle, Tonle Sap Lake in Cambodia, central Laos, and along Vietnam’s coast. Severe salinity intrusion affected Vietnam’s coastal provinces, causing many Mekong Delta residents to struggle with a lack of fresh water.

Hydropower production and water flow significantly impact drought conditions in the Mekong, though the extent varies seasonally. According to the Stimson Center’s Mekong Dam Monitor (MDM) reports, the 2024 dry season saw the lowest hydropower releases in three years. This was mainly due to the 2023 wet season drought in China, which resulted in reduced hydropower production, and the near-complete filling of the Tuoba Dam’s reservoir during the dry season. Consequently, river levels along the Thai-Lao border, from Chiang Saen to Nakhon Phanom, dropped significantly, potentially disturbing the ecological balance in those areas. 

However, these lower hydropower releases from China maintained near-normal river levels in March and April. This is beneficial, as dam releases for hydropower production in the Mekong over the last decade have artificially increased river volumes to two to three times the average March flow, causing severe environmental impacts, especially to Cambodia’s flooded forests. Although the flooded forests’ water levels were lower in 2024 than in recent years, they were still far from normal due to major dam releases upstream, leading to negative ecological consequences for the flooded forest. The reduced releases this year brought some relief, allowing the forests to dry out from previous wet season inundations, yet the ongoing impacts from upstream activities continue to pose significant threats to the forest ecosystem.

The lower-than-normal dam releases for hydropower production further reduced China’s contributions to the Mekong’s dry season flow this year, which were already diminished due to abnormal natural flow conditions. According to the MDM, China’s Tuoba Dam began filling in early February 2024, restricting 1.215 billion cubic meters of Mekong flow to bring the reservoir to its normal service level in under six months. Further downstream restrictions occurred when China started refilling the largest dam in the Mekong, the Nuozhadu Reservoir, unseasonably early in late April. 

The early refilling of the Mekong River should have been observed downstream, but it was instead held back by China’s Tuoba and Nuozhadu dams. While this strategy benefits China by saving water for hydropower production during the 2025 dry season, it has detrimental effects downstream. A significant restriction of 892 million cubic meters at the Nuozhadu Dam matched the combined releases of all other dams, resulting in a near-net zero change in water flow across the basin. 

This disruption has the potential to significantly disturb the natural cycles of many ecosystems throughout the region. As most of the lower basin experienced continued drought throughout the first three weeks of June, China’s water restrictions exacerbated the already dire conditions in the lower Mekong.

Additionally, for 11 consecutive days in May, China’s Jinghong Dam employed hydropeaking – a practice of releasing water in sudden bursts during afternoon and evening to maximize hydropower generation when electricity demand is highest, followed by restricting water overnight. This manipulation of water flow introduced sharp peaks and valleys to the Mekong River’s ecology, causing severe disruption to fish habitats and impeding fish migration.

All such developments and problematic operations of hydropower dams in the upstream Mekong correspond well with many independent reports that conclude that the dam operators do not actually reflect on either the impacts of their manipulation of water flow, or the position and needs of downstream fragile ecosystems and farming communities.

A Double Water Crisis in Vietnam’s Mekong Delta and Policy Recommendations

Throughout this year’s dry season, most of Vietnam’s Mekong Delta remained wet due to irrigation for the spring rice crop. Drawing on recent experiences with droughts, Vietnam made substantial preparations to mitigate the drought’s impact and protect agricultural production. 

Despite these efforts, a severe dryness emerged in the delta’s coastal provinces due to decreased water supply from the upstream Mekong and salinity intrusion, which rendered rivers and canals useless for irrigation. Fields in these regions, deprived of freshwater, were drying out rapidly. Consequently, nearly a million delta residents in Tien Giang, Ben Tre, Soc Trang, Tra Vinh, and Ca Mau provinces were facing a critical shortage of freshwater for daily use.

The Mekong Environment Forum drew on the recent Policy Dialogue co-hosted by the Stimson Center and International Union for Conservation of Nation (IUCN) in Ho Chi Minh City for several policy recommendations for Vietnam to mitigate the double water crisis.

First, the government of Vietnam should partner with neighboring governments and international research organizations to produce authoritative assessments of the double challenge posed by hydropower and climate risks for affected communities and ecosystems.

Second, the government should leverage the Mekong Agreement 1995 and international law on transboundary waters to collaborate with riparian governments and dam operators to maintain minimum flows on transboundary rivers, thereby protecting key downstream habitats and agricultural hubs from destruction.

Third, the government should explicitly support and permit alternative farm systems in areas of water scarcity and soil degradation in the Mekong Delta, including allowing dry season crop rotation and adjusting export policy targets to support alternative crops.

Fourth, the government and foreign development partners should invest in technical systems for early warning systems and improve management responses for disaster response.

Fifth, provincial authorities in the Mekong Delta should support adoption of alternative crops through providing policy guidance for farmers. They can do so by enabling and encouraging the support from research institutes, NGOs, and independent experts, and vocational training organizations who can provide technical and financial support for farmers looking to shift to more sustainable approaches such as improved irrigation and crop diversification.

By Nguyen Minh Quang & Nguyen Phuong Nguyen & Le Minh Hieu, & James Borton – The diplomat -July 27, 2024