Recent global weather patterns, marked by relentless storms and heavy rains, have significantly impacted multiple regions, including Asia. Meteorologists attribute these changes to the transition from El Niño to La Niña, indicating the onset of a neutral El Niño Southern Oscillation (ENSO) state.
El Niño is characterised by the abnormal warming of sea surface temperatures in the central and eastern equatorial Pacific, typically lasting eight to twelve months and occurring approximately every three to four years. La Niña represents the opposite phase, involving the cooling of the same oceanic region, though the frequency of its occurrence can vary.
In Vietnam, experts predict that La Niña will complicate rain, storm, and flood patterns, particularly in the central region, from now until the end of the year. Increased rainfall, including intense downpours, is expected to heighten the risk of flooding and urban inundation.
According to the World Meteorological Organization (WMO), El Niño weakened and transitioned to a neutral ENSO state between April and June 2024, with a 75-80 percent likelihood of La Niña developing between July and September. The probability of La Niña occurring is estimated at 55-65 percent.
This transition has already resulted in extreme weather conditions globally. Several regions have experienced prolonged heavy rains, floods, and landslides. In the Philippines, the national weather authority has predicted that La Niña will commence in August and extend into the first quarter of 2025, likely intensifying tropical storms and heavy rains. Some areas have already recorded unusual rainfall patterns since late July.
Similarly, mid-July rains in eastern Afghanistan led to at least 35 deaths, hundreds of injuries, and extensive damage to property and crops. China's national meteorological agency has issued warnings for heavy rains and high temperatures across multiple regions, with over 200mm of rainfall in some areas. South Korea has also faced record rainfall, unprecedented in the past 200 years.
Meteorological experts warn that during La Niña, many areas may experience significant rainfall and sudden drops in temperature, even in summer.
WMO spokesperson Clare Nullis has said that extreme weather is becoming the "new normal" as natural disasters increase in frequency. The heatwaves of summer 2023 and April-June 2024, driven by El Niño, are now giving way to the heavy rains, tropical storms, and other associated disasters typical of La Niña.
Vietnam's complex weather forecast
In Vietnam, meteorologists have been warning of the transition to ENSO and subsequently La Niña since late this year when El Niño was nearing its end. Associate Professor Dr Pham Thi Thanh Nga, director of the Institute of Hydrometeorology and Climate Change, noted that previous significant La Niña events, such as those from 1998-2000, 2007-08, 2010-11, and 2020-22, were each associated with unusual weather phenomena.
For example, a severe cold spell in January-February 2008 lasted 38 days, devastating 180,000 hectares of rice and killing nearly 110,000 livestock, with damage estimated at VND400 billion (nearly US$16 million).
The 2020-22 La Niña period also saw substantial losses, including 14 storms and tropical depressions, 120 flash floods and landslides, 265 thunderstorms, whirlwinds, and lightning strikes, leading to 357 deaths and over VND39,960 billion in damage. In 2022 alone, natural disasters claimed 175 lives and caused nearly VND19,500 billion in economic losses.
"La Niña is expected to impact Vietnam between September and November 2024, coinciding with the typhoon season in the central region. This is likely to result in complex rain, storm, and flood patterns, with potentially higher-than-normal rainfall, raising the risk of flooding and urban inundation", Mai Van Khiem, director of the National Center for Hydro-Meteorological Forecasting, said.
Even though Vietnam has only recently entered the neutral ENSO phase, the country has already experienced unusual weather patterns, according to the center's observation.
June-July is typically the main rainy season in the North, accounting for 30-35 percent of the year's total rainfall. However, the global atmospheric system's disruption during the transition from El Niño to ENSO and La Niña is affecting Vietnam, leading to recent abnormal rainfall and flooding.
Khiem cautioned that hazardous natural disasters were expected in the final months of the year. From now until the end of September, the North would likely experience significant rainfall, with risks of flash floods and landslides in mountainous areas.
Looking ahead, he said, La Niña was anticipated to develop and affect Vietnam during the peak rainy and typhoon season in the central region, leading to complex storm, rain, and flood patterns. Increased rains along the central coast were expected, raising the likelihood of flooding and urban inundation. With the rise in rainfall, the risk of flash floods and landslides would also increase, particularly in mountainous regions with unstable soil. La Niña might heighten the frequency and intensity of storms and tropical depressions, especially towards the year's end, he said.
From now until the end of 2024, eight to ten storms or tropical depressions are forecast in the East Sea (known internationally as the South China Sea), with four to five potentially affecting Vietnam mainland, posing threats to maritime activities and coastal aquaculture. Furthermore, extreme thunderstorms on land and at sea, along with intense short-term rainfall causing urban flooding, are predicted to become more frequent, impacting socioeconomic development.
Proactive preparedness needed
Nguyen Van Hai, head of the Disaster Response and Recovery Division at the Department of Dike Management and Natural Disaster Prevention and Control (under the Ministry of Agriculture and Rural Development), emphasised the need for proactive preparedness measures, particularly in the northern mountainous provinces. He stressed the importance of improving public awareness, guiding residents and local authorities, reviewing high-risk areas for evacuation, and clearing obstructed water channels.
In the event of a disaster, local authorities should remain vigilant, deploying forces to monitor, guide, and oversee response efforts, he said.
For the central provinces and other regions, Mr. Hai called for immediate action to review storm and flood response plans. He underscored the importance of active public participation and the crucial role local governments play in ensuring safety and effectiveness in current disaster preparedness efforts.
