The La Niña-like signal is still prominent and coherent as of May 2022. According to the latest NOAA Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI), the ENSO Alert System Status is currently stated as “La Niña Advisory.”
However, although La Niña is favoured to continue, the odds for La Niña decrease into the late Northern Hemisphere summer (58% chance in August–October 2022) before slightly increasing through the Northern Hemisphere fall and early winter 2022 (61% chance).
Bangladesh is an ENSO sensitive country and is normally flooded during a La Niña year. All major floods which have occurred in Bangladesh were La Niña years (eg, 1988, 1998, 2016). However, there were also floods during El Niño years (eg, 1987, which was a central Pacific El Niño or Warm Pool El Niño, a.k.a. El Niño-Modoki).
Normally, El Niño years are dry years in Bangladesh and the country often faces drought and severe water shortages in any major El Niño year (eg, 1982–83, 1997). Note that the major El Niño events are known as Eastern Pacific El Niño (or Cold Tongue El Niño).
Currently, we have a moderate La Niña year and above normal rainfall and flooding are possible. According to the World Meteorological Organization (WMO) and the authoritative seasonal forecast from the South Asian Climate Outlook Forum, normal to above-normal rainfall is most likely during the 2022 southwest monsoon season (June–September) over most parts of South Asia.
The current extreme heat in India, Pakistan, Bangladesh, and other parts of Asia may also trigger glacial floods. This glacial flooding may aggravate normal flooding problems. The combined impact of strong La Niña-related heavy rainfall and extreme-heat-related glacial flooding was the major cause of basin-wide catastrophic flooding in 1998.
Similarly, the combined impact of moderate La Niña-related rainfall and heat-related glacial flooding was partially responsible for a moderate flooding event back in 1988.
Critical analyses of the ocean and atmospheric dynamics for the years of 1987, 1988, 1998, and 2022 by myself show that there is close correspondence between the sea surface temperatures (SSTs) anomaly in the eastern Pacific Ocean in the Niño 3.4 region between the year 1988 and 2022 (Fig. 1).
The figure shows the presence of colder-than-normal SSTs (blue shading) in the eastern Pacific in January through April of 2022. It is noticeable that similar cold SSTs appeared to dominate between May to August in 1988. Colder than normal SSTs in the Niño 3.4 region during January through April of 1988 (not shown) were also documented, but temperatures in 2022 were colder.
Therefore, it is more likely that if we see the current SST pattern in Niño 3.4, the region will stay the same for another three months with a high probability of a flood like that of 1988 following soon after. According to CPC/IRI forecasts, La Niña is favoured to continue for another three months (58% chance in August–October 2022).
Per my calculations, the current forecast for flooding in 2022 can be presented in the three tercile format as 40:40:20, which means there is 40% probability for higher-than-normal flooding, 40% probability for normal flooding, and 20% probability for lower-than-normal flooding.
Md Rashed Chowdhury is Adjunct Professor in the School of Sustainable Engineering and the Built Environment of Arizona State University.
