The Mekong Delta region has previously endured two severe seasonal droughts caused by El Niño in 2015-2016 and 2019-2020. However, experts are now predicting the likelihood of a “super” El Niño occurring this year, which could lead to even more severe drought, saltwater intrusion, and shortages of sand and alluvial sediments. These factors would have negative impacts on electricity generation in hydropower plants and crop production in the following year.
Throughout the 20th and 21st centuries, there have been only two instances of “super” El Niño phenomenon occurring, in 1982-1983 and 1997-1998. Climate experts are expressing concerns that a third “super” El Niño could emerge in 2023.
On June 8, 2023, the U.S. National Oceanic and Atmospheric Administration (NOAA) officially declared the onset of El Niño, as evidenced by numerous storms in the Pacific Ocean, forest fires in Indonesia, and heatwaves in various countries, including Vietnam.
Understanding El Niño
El Niño and La Niña represent opposite extremes in the El Niño/Southern Oscillation (ENSO) cycle, which refers to cyclical environmental conditions in the Equatorial Pacific Ocean. El Niño, meaning “little boy” in Spanish, is the warm phase of the ENSO cycle and brings warmer-than-average temperatures.
On the other hand, La Niña, meaning “little girl,” represents the cold phase and is characterized by cooler-than-average ocean temperatures. El Niño and La Niña alternate every two to seven years on average. El Niño events are more frequent than La Niña events. The absence of both El Niño and La Niña is known as the neutral phase of the ENSO cycle.
Impacts of El Niño on the Mekong Delta region
The strength of the upcoming El Niño is still uncertain. Some experts predict it could reach super-strength, while others suggest it will be more moderate. In the event of a “super” El Niño, the Mekong Delta basin will experience a significant reduction in rainfall from June to November 2023. The stronger the El Niño, the less rainfall the region will receive. If this year’s El Niño is as extreme as those in 2015 and 2019, the upcoming rainy season’s rainfall will be as low as in those years, resulting in a severe dry season in 2024, similar to 2016 and 2020.
The reduced rainfall in the Mekong River region will lead to lower flood levels and water levels. Consequently, there will likely be a decrease in the number of aquatic animals flowing into the rivers, negatively impacting their reproduction. The amount of alluvial sediment carried by the river to the delta during the flood season will also be reduced, resulting in a shortage of sand in the region.
The low flood stage will have adverse impacts on agricultural practices, fish and shrimp farming, and tourism activities in the Plain of Reeds (Dong Thap Muoi) and the Long Xuyen Quadrangle area. Moreover, the lack of floodwaters and alluvial sediments this year will hinder crop production in the following year.
As the dry season of 2024 approaches, coastal areas will face the main concern of saltwater intrusion. Addressing this risk requires specific considerations for the Mekong River estuary and the Ca Mau Peninsula.
The Mekong River estuary is greatly influenced by water flow changes from the upper parts of the river and the operation of hydropower reservoirs upstream. During the El Niño weather phenomenon, decreased rainfall leads to reduced flood levels in the rainy season and low water levels in rivers and lakes during the dry season.
The lower water levels in hydropower dams adversely affect turbine operation for electricity generation, necessitating an extended period of dam closure to accumulate sufficient water. This exacerbates the issue of saltwater intrusion in the Mekong Delta. In other words, the operation of hydropower dams along the rivers worsens saltwater intrusion, particularly during the dry season.
In years with severe El Niño events, saltwater intrusion prevention measures in the Mekong Delta region are only effective at the beginning of the dry season. Despite efforts to block saltwater intrusion from the sea during the dry season, the Mekong Delta continues to experience severe freshwater shortages by the middle of this period.
The Ca Mau Peninsula is less influenced by the Mekong River’s water flow. The water supply in this region mainly relies on rainfall, and the soil is mostly saline. The soil becomes non-saline on the surface for approximately six months each year due to rainwater. However, during the dry season, the soil becomes saline as freshwater ebbs. In years with lower rainfall, the freshwater layer recedes more rapidly.
Saltwater intrusion prevention measures also work effectively only at the beginning of the dry season. As the dry season progresses, saltwater intrusion worsens, even when seawater inflow into the area is successfully blocked. Additionally, saltwater from the underlying saline soil rises, exacerbating the salinity issue in this area.
Tackling El Niño
Although the strength of El Niño is yet to be determined, the agricultural sector should closely monitor its influence and be prepared to respond promptly. Those in flood-prone areas, especially the Plain of Reeds and the Long Xuyen Quadrangle, should exercise caution when making investments in agriculture and livelihoods dependent on the upcoming flood season. Natural fishing activities should also be approached with careful consideration of purchasing nets and fishing equipment.
In the 2024 dry season, the primary concern for the Mekong Delta region will be the severe risk of saltwater intrusion along the coastal areas, along with its consequential impacts. It is crucial to learn from past experiences, such as the significant damages caused by the extreme El Niño events during the rainy season of 2015 and the subsequent severe dry season in 2016. Proactive measures, such as adjusting cropping periods in advance and storing freshwater for use during the dry season of 2024, can help mitigate the impacts.
In the long term, implementing the development plan for the Mekong Delta, announced by the Prime Minister in June 2020, is necessary. This plan includes the reallocation of land for agricultural farming, shifting crops and aquafarming to non-saline soil and freshwater areas further inland, while designating brackish zones for saltwater farming.
The agricultural farming practices will be adapted to varying salinity levels, alleviating concerns of saltwater intrusion during the dry season. Additionally, significant investment should be made in providing freshwater for domestic use in coastal areas to reduce groundwater exploitation, thereby mitigating land subsidence in the delta, particularly in light of rising sea levels.
Source: The SaigonTimes