Securing water resources amid El Niño: [1] Mounting pressure

The El Niño phenomenon officially returned in June 2026 and developed rapidly, transitioning from neutral conditions to El Niño in just three months. This evolution closely resembles several strong historical El Niño events, including those of 1982-1983, 1997-1998, 2015-2016, and 2023-2024.

Severe rainfall deficit expected nationwide

In Viet Nam, El Niño exerts pressure not only through rising temperatures but also through a chain of cumulative impacts that threaten water security. These include below-average rainfall, increased evapotranspiration, reduced river flows, difficulties in replenishing reservoir storage, saltwater intrusion, and rising water demand during the dry season.

According to forecasts, most regions are expected to experience widespread rainfall deficits of 10-50%. The rainy season is likely to end earlier than usual in the South Central Coast, Central Highlands, and Southern regions. During the final two months of 2026, Northern Viet Nam and the provinces from Thanh Hoa to Ha Tinh may receive 10-30% more rainfall than the long-term average, while most other regions are expected to record 10-40% below-average rainfall.

With these rainfall patterns, most river basins are forecast to experience water shortages, with water availability expected to remain several tens of percent below the long-term average.

Reduced rainfall lowers river flows and intensifies water shortages

Declining rainfall reduces river flows and directly limits the replenishment of reservoirs, soil moisture, and water supplies for agriculture and domestic use. If the rainfall deficit persists, many river basins could enter the dry season with already depleted water resources, while higher temperatures and growing water demand further increase pressure on available supplies. However, the extent of rainfall shortages will need to be updated monthly and by region, as precipitation under El Niño is unevenly distributed across both time and geography.

Alongside reduced rainfall, the nationwide average temperature is expected to remain 0.5–1.5°C above the long-term average. Prolonged and widespread heatwaves are likely, particularly across Northern Viet Nam, the North Central, Central, and South Central Coast regions. Higher temperatures accelerate evapotranspiration, reduce soil moisture, and cause stored water to be depleted more rapidly. At the same time, demand for water for domestic use, agriculture, and energy production typically increases during heatwaves, placing additional strain on already diminishing natural water resources.

The rainfall deficit associated with El Niño is expected to result in more severe water shortages in river basins along the coastal provinces from Quang Tri to Lam Dong, throughout the Central Highlands, and across the Mekong River Basin and the Mekong Delta. Reduced inflows, combined with the likelihood of an early end to the rainy season, could adversely affect water storage in irrigation and hydropower reservoirs.

Saltwater intrusion could extend nearly 100 km inland

According to Hoang Duc Cuong, Deputy Director General of the Viet Nam Meteorological and Hydrological Administration, the current El Niño event warrants nationwide attention, although Central and Southern Viet Nam are expected to bear the greatest impacts, consistent with historical patterns.

In the central region, below-average rainfall, declining river flows, and the likelihood of an early end to the rainy season will reduce reservoirs' ability to store water. Some small and medium-sized reservoirs may struggle to supply sufficient water for domestic use and agricultural production toward the end of the 2026–2027 dry season.

The latest assessment indicates that rainfall over the upper Mekong River Basin during the 2026 flood season will likely remain below the long-term average. As a result, dry-season flows in the lower Mekong during 2026–2027 are projected to decline by 10–30% compared with normal conditions. This could trigger an earlier onset of saltwater intrusion, with saline water penetrating up to nearly 100 km inland, depending on the river branch, posing significant risks to agricultural production.

From January 2027, areas with salinity levels exceeding 4 g/L are expected to appear 25–30 km from the coastline.

From the 2016 drought to the imperative of safeguarding water security

The 2026–2027 El Niño event is forecast to be as intense as the 2015–2016 episode, or potentially even stronger. The drought and saltwater intrusion during 2015–2016 remain a stark reminder of the unprecedented severity of such events. The crisis - the worst in more than six decades affected 52 of Viet Nam's 63 provinces at the time, with 18 provinces suffering severe impacts. Approximately 2 million people experienced acute domestic water shortages and required emergency assistance, while saltwater intrusion affected all 13 provinces in the Mekong Delta.

According to Mai Van Khiem, Director General of the National Center for Hydro-Meteorological Forecasting, the Mekong Delta was struck by another severe drought and salinity intrusion during 2019–2020, following the 2015-2016 El Niño. However, the timely issuance of forecasts and early warnings, proactive water resource management, climate-adaptive adjustments to agricultural production, and the implementation of preventive measures significantly reduced the impacts on the economy, society, and people's livelihoods.

Proactive measures needed to prepare for water shortages

To prepare for the projected rainfall and water shortages in the coming months, the meteorological and hydrological authority has urged ministries, sectors, and local governments to continuously monitor seasonal and monthly meteorological and hydrological forecasts and develop response plans without delay.

Specifically, authorities are advised to review reservoir storage capacity at each stage, develop water allocation plans based on priority needs, promote water conservation, prepare power system operation plans for periods of extreme heat, and closely monitor the early onset of saltwater intrusion in the Mekong Delta.

For the agricultural sector, proactive measures include storing and conserving freshwater in reservoirs and river systems, while prioritizing water distribution for essential domestic use and the critical flowering stage of major crops.

For industry and the energy sector, reduced inflows to hydropower reservoirs could limit hydropower generation capacity, particularly during the peak electricity demand period of May-June 2027. Water storage in reservoirs on the Da, Dong Nai, Se San, and Serepok river systems could fall below the long-term average if the El Niño event becomes exceptionally strong and prolonged. In such a scenario, the power system may need to rely more heavily on thermal power plants and other higher-cost generation sources, increasing electricity production costs and affecting business efficiency. Localized water shortages could also disrupt water-intensive industrial operations.

Although the intensity and duration of the 2026-2027 El Niño event remain uncertain, mounting pressure on water resources is already evident through declining rainfall, reduced river flows, challenges in replenishing reservoirs, and an elevated risk of saltwater intrusion. The remainder of the rainy season, therefore, represents a critical window for assessing water supply capacity, maximizing water storage, and preparing contingency plans. The 2016 experience demonstrated that safeguarding water security must begin before drought and water shortages become severe.