Some of Asia's largest cities are likely to face months of drought while others could be hit by flooding when a “super” El Niño weather event develops later this year, according to research that warns it has no precedent on record. The analysis, released by WaterAid and carried out by academics at the universities of Bristol and Cardiff, examined 44 years of rainfall in 12 South and South-East Asian cities alongside the strength of past El Niño events, and found that the stronger the El Niño event, the more certain it became that a city's rainfall would swing away from normal. However, cities swung in opposite extremes, the researchers found, with some pushed towards drought and others, sometimes only a few hundred miles away, pushed towards flooding.
Jakarta and Surabaya in Indonesia; Phnom Penh in Cambodia; Bangkok in Thailand, Kuala Lumpur in Malaysia and Mumbai in India all became drier as El Niño strengthened, with the very strongest events clustering at the driest outcomes in the data. Meanwhile, Shanghai and Hangzhou in China and Colombo in Sri Lanka went the other way, becoming reliably wetter. Faisalabad and Karachi in Pakistan and Dhaka in Bangladesh sit between the two zones and have swung either way, which makes them the hardest for governments to plan for.
El Niño begins with a warming of the surface of the Pacific and ends up moving moisture around the planet in ways that leave some regions in flood and others in drought, depending on where they sit relative to that movement. It occurs every five to ten years, and its strength is measured by how far sea surface temperatures deviate from normal. What makes this year different is the scale of the event, which is already being labelled “super” this year.
Meteorological agencies and researchers around the world are on high alert that this El Niño has gained strength at an exceptional speed, and could affect every weather pattern. It could reach as high as 3.6C above normal, against a previous monthly record of 2.75C set during the El Niño of 2015 and 2016. Nothing on record approaches what is forecast, which the researchers say leaves the size of the impact genuinely uncertain.
"Under the unprecedented super El Niño, we are in unchartered territory because there is no event on record as large as what is predicted," the researchers said. "There are definitely uncertainties relating to the magnitude of the impact. However, based on our analysis, there seems to be more certainty related to the direction of the impact.
Regions normally prone to drought will highly likely experience drought and regions normally prone to flooding will highly likely experience flooding." "When we get to territory like a super El Niño, it means that that difference in sea surface temperatures, that anomaly that we're measuring across the globe, is really extreme," said Michael Singer, professor at Cardiff University and one of the lead scientists. "So we're expecting a lot more moisture to be moving around in very specific ways around the planet, leading to in some places, you know, probably really high propensity for flooding, and in other places, a high likelihood of drought." For the South Asian cities in the drying group, the effect will interrupt a pattern running the other way. WaterAid's earlier research found most of these cities have been getting steadily wetter over four decades, with fewer droughts and more extreme rainfall.
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