Effects of El Niño on the Mekong Delta

El Niño and the Southern Oscillation (ENSO) is a periodic variation in winds and sea surface temperatures over the equatorial Pacific Ocean. ENSO has wide-ranging effects on the climate of much of the tropics and subtropics (Lindsey, 2016). This project focuses on how El Niño affects the Mekong Delta.

The presence of an ENSO is defined by 0.65°C difference for 5 or more consecutive months from the 3-month average sea surface temperature (ASMC, n.d.).

No two instances of ENSO are the same, and this variability is likely to only get amplified in face of future climate change (McPhaden, 2023).

Located in the south of Vietnam, the Mekong Delta is one of the most fertile pieces of land in the world. Fresh water is provided by the Mekong River - the “Nile of Asia” - which spans 2,700 miles (4,350 km) and 6 nations.

The Mekong River meets the South China Sea in the flat alluvial plane of the Mekong Delta in 9 distributary channels. This leads to its local Vietnamese name of Sông Cửu Long (lit. “Nine Dragons River”).

Spanning 4 million hectares, the Mekong Delta is home to 18 million people and a rich variety of plant life and wildlife. Mekong Delta is a major producer of agricultural products, notably the biggest rice paddy in Vietnam.

Southern Vietnam experiences two distinct seasons:

• a dry season from November to April, and
• wet season from May to November.

The Delta commonly faces hazards of both drought and floods (Wikipedia, n.d). Harsh conditions are further intensified by ENSO, exacerbating challenges in agricultural cycles. 

Another major factor in restricted downstream flow are dams on the upper Mekong, built by China (Eyler, 2020). With China’s considerable power, 60 million people living downstream have limited say in asking China to release water from the dam. The Vietnamese government also attributes droughts in lower Mekong region to El Nino and climate change (Eyler, 2020), not Chinese dams.

Figures 9 compares the Mekong Delta during the drought year of 2019 to previous ENSO-neutral years.

The Mekong Delta’s located at the mouth of the Mekong River where it meets the South China Sea. During the dry season, reduced seaward movement of freshwater from upstream allows saltwater to encroach on the delta's river systems. Figure 10 represent the salinity threshold of 4 gram/liter for the years 2016 (yellow), 2020 (blue), 2021 (2021). Beyond this threshold, water becomes unsuitable for agricultural and domestic purposes.

El Niño conditions started in late 2023 in Vietnam, with a high likelihood of persisting into 2024 (Nhân Dân cuối tuần, 2023):

• Higher than average temperatures nationwide from January to June.
• Rainfall from January to March experiencing a 10-20% decrease, and April to June facing a 15% reduction.
• The flood season is anticipated to be lower, increasing the likelihood of elevated and early saltwater intrusion (H. Phuong, 2024).

Overall, the impacts of ENSO on the Mekong Delta are becoming increasingly severe and complex each year. However, harsh and unpredictable weather has long been a hallmark of this region. Both the government and its citizens have shown adaptability to past severe events and have actively prepared for future conditions. Therefore, I believe that the Mekong region's ability to cope with 2024's ENSO condition will be better than in previous years.