SINGAPORE: For Singapore, 2024 was a year of record-breaking temperatures and unusual rainfall patterns – from July logging its first dry spell since 2019, to soaring temperatures and less rain in December.

The wettest November in more than 40 years was also recorded in 2024, while two unusual episodes in September and October led to intense rain, the weatherman’s annual climate assessment report showed.

Across the whole year, total rainfall at 2,739.8 mm was higher than the long-term average of 2,534.3 mm, said the report released on March 23.

While soaring mercury is a symptom of global warming, the unusual rainfall patterns of 2024 could not be linked directly to climate change, the Meteorological Service Singapore (MSS) told The Straits Times.

This is because Singapore’s rainfall is highly variable, with strong dependence on large-scale climate drivers such as the El Niño-Southern Oscillation – a global climate cycle involving changes in winds and sea surface temperatures in the tropical Pacific Ocean.

This driver comprises the warming El Niño and rainy La Niña climate phenomena.

MSS added: “Although we project more frequent extreme rainfall patterns in the long term, individual rainfall events cannot be attributed directly to climate change.”

But overall – as revealed by the MSS in January – 2024 was the warmest year in Singapore, tying with 2019 and 2016, with the temperature hitting an annual mean of 28.4 °C.

A sizzling 2024

2024 also marked the fourth year in a row that Singapore’s mean temperature over a decade reached a new high. The year also saw the warmest July and December on record.

The warmer-than-usual conditions are likely associated with the El Niño period, which lasted from the second half of 2023 to around April 2024.

During an 18-day dry spell in July, the daily highest temperature ranged between 32.8 °C and 35.2 °C. Nights were warm as well, with the lowest daily temperature topping 28 °C in most areas.

While December 2024 was one of the cooler months of the year, it also saw a temperature record broken.

On Dec 7, the mercury hit a scorching 36.2 °C in Paya Lebar, breaking the record for the highest daily temperature in December.

From dry spell to deluge

The July 13-30 dry spell was influenced by at least three tropical cyclones that formed in the northern part of the South China Sea around that time, which included Typhoon Gaemi.

The resulting stronger winds and the movement of drier air into the region led to the 18-day dry spell, said the climate assessment report. The last dry spell in Singapore lasted 17 days from July 31 to Aug 16 in 2019.

December also marked an unusually dry end to the year, with the month’s average rainfall 30 per cent below the long-term average.

But the preceding month was the wettest November in more than 40 years, with an island-wide average rainfall of 419mm.

The MSS report said a weather phenomenon called the Madden-Julian Oscillation (MJO) had significantly contributed to the higher rainfall that month.

The MJO refers to a pulse of cloud or rain that moves eastward around the Equator, with a typical cycle lasting one to two months – bringing more rain than usual to Singapore when it passes over the country.

The report said the MJO possibly contributed to 42 per cent of November’s rainfall.

Experts say it is tricky to detect the fingerprints of climate change on rain events here.

Dr Koh Tieh Yong from the World Climate Research Programme said: “Many more years of concerted data collection and analysis are needed to tease out the man-made signal of climate change from the natural ‘noise’ of our tropical rainfall.”

Rainfall fluctuations amid climate change are linked to the redistribution of water vapour rather than an overall increase or decrease in downpours, noted Dr Koh, who co-chairs the research programme’s Asian-Australian Monsoon working group.

Water vapour in the air is redistributed as winds and vertical airflow evolve. This then upsets regional and seasonal rainfall patterns in the tropics, he explained.

For example, in a certain month, there may be more or less rainfall at a location as the climate readjusts.

The MSS report also highlighted two rain events that were short-lived but had significant impact island-wide.

On the evening of Sept 17, a blustery Sumatra squall swept across the whole of Singapore within 1½ hours, bringing widespread thundery showers and gusty winds that affected more than 300 trees island-wide. East Coast Parkway felt the strongest wind gust of 83.2 kmh.

A Sumatra squall is a line of thunderstorms that develops over Sumatra or the Strait of Malacca.

The September squall was so fast moving that the average rainfall was only about 10.3 mm. The storm caused the temperature to drop rapidly from around 30 °C to 25 °C – mostly within five minutes.

More than 300 tree-related incidents – including felled trees and snapped branches – were reported.

Separately, on Oct 14, island-wide thunderstorms emerged around midnight and continued into the afternoon.

The deluge caused flash floods in many areas such as Tampines and Bukit Timah.