Haze in Singapore retreats with rainy weather's arrival

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SINGAPORE — Singapore has likely been spared the brunt of the haze in 2023 with the arrival of wet weather, said the weatherman.

While El Nino is expected to last at least until the start of 2024, there is still uncertainty about its exact duration and whether it will have an impact on the haze situation next year, said the Meteorological Service Singapore (MSS).

"As we go into the inter-monsoon period between the latter part of October and November, the winds become light and variable, and there is an increase in showers which reduces the likelihood of transboundary haze, especially with wet weather in the coming weeks," MSS told The Straits Times.

The next period with a higher haze risk will be during the south-west monsoon between June and October 2024, which coincides with the dry season for the region.

This is despite the arrival of the El Nino weather phenomenon, which is known to exacerbate dry conditions and increase the chances of haze.

So far, air quality in Singapore hit unhealthy levels on only one day in 2023 — and for the first time since 2019 — on Oct 7 when the 24-hour Pollutant Standards Index (PSI) readings ranged between 67 and 123 at 9pm.

A PSI reading of 101 to 200 is in the unhealthy range.

Thunderstorms have already descended upon Singapore, with more showers forecast over the next few days.

This should keep the regional hot spots and haze situation subdued, the agency noted.

Singapore, like Indonesia, experiences two main monsoon seasons — the north-east monsoon, which typically occurs between end-November and March, and the south-west monsoon, between June and October. 

The two seasons are separated by transition (inter-monsoon) periods. 

MSS noted that Singapore faces a higher risk of transboundary haze during the south-west monsoon when the region experiences its dry season. 

"During this time, the winds over Singapore blow mainly from the south-east or south-west, and there is a risk of smoke haze affecting Singapore if there are fires in Sumatra or Kalimantan," said an MSS spokesman. 

While a major source of the haze comes from Indonesia's burning of peatlands, which become extremely flammable when they are dried out for agriculture, climate drivers such as El Nino may intensify the dry conditions, increasing the risk of fires.

At other times, the risk of haze is lower.

During the north-east monsoon, the risk is low because winds over Singapore predominantly blow from the north or north-east, avoiding the hot spots. 

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During the inter-monsoon months of March and April, the likelihood of Singapore being affected by transboundary haze is also low due to wetter conditions in the surrounding region, the spokesman noted.

However, because light wind conditions are more common during these inter-monsoon months, there may be brief periods when particulate matter accumulates in the air, resulting in hazy conditions. This would typically occur overnight and in the early morning, said the agency.

The last three years have seen an unusual run of La Nina events.

La Nina, which brings with it cooler weather, has led to prolonged wet weather in the region, sparing Singapore from major fire or haze events. MSS declared the onset of El Nino on Aug 11.

However, it noted that most El Nino events typically end some time between December and May, and that back-to-back years with La Nina events are usually more common than for El Nino.

Singapore Institute of International Affairs chairman Simon Tay said in a statement that El Nino and the Indian Ocean Dipole, another climate phenomenon which brings about drier weather, can extend to multiple years and may continue to increase haze risk in 2024 or beyond.

"It is wrong to see this as a short-lived nuisance... especially with climate change, the challenge from the haze is real and must be of global concern," said Associate Professor Tay.

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This article was first published in The Straits Times. Permission required for reproduction.