CNA Explains: Why Singapore and Southeast Asia could see a wetter, rainier end to 2024
What does it have to do with the La Nina phenomenon and will it lead to more flooding?
People walk in heavy rain in Singapore on Mar 3, 2023. (Photo: CNA/Jeremy Long)
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SINGAPORE: Singapore's government issued flood risk alerts on Monday (Oct 14) as the inter-monsoon period brought heavy rains and lightning.
Throughout the rest of Southeast Asia, weather forecasters are predicting similarly wetter conditions for the next two months at least, possibly signalling a shift to the start of the La Nina phenomenon.
What is La Nina and how does it lead to heavier rain?
It's a pattern involving tropical Pacific sea surface temperatures, that usually persists for months to about a year, meteorological experts told CNA.
Under normal conditions, the sea in the Western Pacific region is cooler than the sea in the Eastern Pacific region, said Dr Wang Jingyu, an assistant professor of physical geography at the National Institute of Education (NIE).
Under La Nina conditions, the sea surface temperature in the Western Pacific region is warmer by 0.5 to 1 degree Celsius instead.
And the surface temperature of water is warmer, more of it evaporates. This increases moisture in the lower atmosphere, which in turn leads to more rain.
The reverse of La Nina is El Nino, which Singapore experienced from March to April. Here, sea surface temperature patterns are cooler in the Western Pacific and warmer in the Eastern Pacific.
The result is hotter and drier weather.
How long is La Nina expected to last?
La Nina conditions will likely run from October to November onwards, with most models predicting this will persist until early 2025, said the Asean Specialised Meteorological Centre earlier this month.
Above-normal rainfall is predicted for much of the southern region of Southeast Asia during this forecast period, the centre added.
The National Oceanic and Atmospheric Administration (NOAA) in the United States meanwhile is predicting a 60 per cent chance for La Nina to emerge by November and last through January to March next year, said Professor Matthias Roth from the National University of Singapore’s geography department.
What does it mean for Singapore and the region?
Dr Dhrubajyoti Samanta, a senior research fellow with the Earth Observatory of Singapore at Nanyang Technological University, pointed to the NOAA forecasting a weak La Nina in Southeast Asia.
This makes it "very likely" that it won't be very wet or of severe concern beyond a typical La Nina.
Such conditions could even be useful for groundwater recharge - where water infiltrates deeper soil layers - and agriculture; while improving air quality, said Dr Samanta.
But Prof Roth noted that a La Nina over the next few months would coincide with Northeast monsoon season, which is already the wettest part of the year.
Apart from cooler air temperatures, there's an increased likelihood of localised flooding when above-average rainfall coincides with periods of already high sea levels, such as during seasonal high tides, he said.
Dr Wang said some Southeast Asian countries could see a higher risk of flooding in low-lying areas with poor drainage, and landslides or mudslides in mountainous regions.
Apart from the threat to public health and lives, this can also disrupt planting and harvesting schedules or worse, destroy crops, thus reducing agriculture yields and resulting in economic loss.
For example, Malaysia's 2021 floods affected more than 10,000 hectares of farmland, causing rice yield to drop by more than 200,000 tonnes, Dr Wang pointed out.
It would take years to recover the infrastructural damage and rice production is Malaysia is still not at an optimal level, he added.
As it is, most countries in the Indochina peninsula are already dealing with the after-effects of deadly storms in recent months.
Typhoon Yagi brought powerful winds and torrential rainfall to Vietnam, Thailand, Laos and Myanmar in September, killing hundreds and damaging factories and farmland.
And the Philippines was hit by several deadly storms in recent months, including Typhoon Gaemi in July, Yagi in September and Krathon in October.
How should governments respond?
Preferably, proactively, experts said.
For example, early flood warnings issued on Monday by Singapore's national water agency PUB gave people time to prepare, said Dr Wang.
Governments should also conduct flooding preparedness exercises to ensure that emergency responders are ready to respond to any incidents, he suggested.
They should also inspect drainage infrastructure to ensure that it can handle the expected rainfall, and raise awareness about the potential impact of the weather.
What does it mean for long-term climate trends?
The projected La Nina to come is not quite comparable to what Southeast Asia experienced from 2020 to 2022, and 1998 to 2001 previously.
The more recent event led to "once in a century" flooding in Malaysia, causing more than 50 people deaths and several billion dollars in financial losses, said Dr Wang, adding that he would consider this an “extreme” scenario.
Nonetheless, experts noted that Singapore and wider Southeast Asia are experiencing more of both rainfall and warmer conditions due to climate change.
“Located in the deep tropics, Singapore used to be less prone to the effects of climate change compared to other mid-latitude countries," said Dr Wang.
"However, as global warming speeds up, we start to see more frequent occurrences of weather and climate extremes over the island.
“The previously known 'once in a century' events could become once in a decade, or even worse, once a year, in the next few years," he added.
"We need to take action. Every single effort to reduce carbon footprint still counts - before it’s too late.”
