Why is Singapore raining so heavily recently?

SINGAPORE — Intense downpours drenched the whole of Singapore in the past week, with the country recording 225.5mm of rain in Kallang last Tuesday (Feb 28) — the wettest February day ever recorded here.

With the showers expected to last through the first fortnight of March, The Straits Times asks Science Centre Singapore chief executive Lim Tit Meng why it has been raining so much.

Q: Is heavy rain usual for this period?

A: February and the start of March have been unusually wet. The National Environment Agency (NEA) announced on March 1 that for the whole of February, Singapore received around 80 per cent to 280 per cent more rain than average.

Although Singapore experiences the north-east monsoon from December to March, which is frequently associated with heavy rain, the period from February tends to be the dry phase of the monsoon, when the rain belt moves southwards away from Singapore.

This makes the recent storms unexpected, said Associate Professor Lim.

Q: Why has it been raining so heavily?

A: Monsoon surges have been the primary cause of these wet spells, said Prof Lim. These surges refer to a sudden increase in wind speeds, which causes cold air to gust into the South China Sea.

NEA said the latest surge on Feb 28 was caused by heightened atmospheric pressure over the northern Asian continent, which can lead to strong winds.

As the cold air moves south, it warms and gathers moisture, forming dense rain clouds over equatorial locations like Singapore, resulting in the rainy and windy "air-con-like" climate here.

The current La Nina conditions could also have contributed to the downpours, said Prof Lim, referring to the weather phenomenon that occurs every two to seven years, when large-scale cooling of surface temperatures in the central and eastern equatorial Pacific Ocean bring about wetter conditions in South-east Asia.

Q: Did climate change play a role in the exceptionally wet weather?

A: "Climate change affects typical seasonal occurrences like our monsoons," said Prof Lim, adding that the surprising amount of rain collected in February is another example of how climate change has made our weather more extreme and unpredictable.

Hot periods become hotter and the wet periods become wetter, and the weather can swing between these two states more erratically, he added.

"It contributes to untraditional weather patterns, where a hot and dry month suddenly becomes cold and wet, and a month that is usually already cold and wet becomes even more so."

The Climate Changed exhibition running at the Science Centre since October highlights the real and present threat of the climate crisis, consequences of inaction, and sustainable steps that people can take to counter its impact, said Prof Lim.

"At the end of the day, our choices as individuals have also contributed to climate change. Hence, every one of us needs to play a part in fighting it, whether it is by making lifestyle changes or by talking to our relatives about it."

Q: How does the weather and the changing climate affect our health?

A: Biometeorology is a branch of science dedicated to studying how weather conditions can affect living things, including our bodies, said Prof Lim.

A theory that cold weather can potentially cause joint aches — which he stressed needs to be validated, as he is not a medical doctor — links that to atmospheric pressure, which drops before it rains.

The resulting lower air pressure causes muscles, tendons and other surrounding tissues to expand, putting them under extra pressure within the constrictions of the body which causes pain.

As climate change causes more unpredictable and extreme weather events, some — especially the elderly — may also fall ill more easily as immune systems struggle to adapt to the erratic changes in the environment, added Prof Lim.

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