SINGAPORE, March 23 — Last year was Singapore’s fourth warmest year on record, tying with 1997 and 2015. May was 2023's hottest month — and both May and October were the warmest on the books for those months historically.

After a cool start to the year, the scorching month of May delivered the year's highest recorded temperature: 37°C on May 13 in Ang Mo Kio. It tied with April 17, 1983 as Singapore's highest recorded temperature.

These were some of the findings in the Meteorological Service Singapore’s Annual Climate Assessment Report for 2023, which focused on the year’s climate trends.

The report noted that the warming trend experienced in Singapore is consistent with global trends.

Other than an unusually scorching May, two other notable weather events impacted Singapore last year — an uncommonly late monsoon surge from late February to early March, and hazy conditions in October.

As temperatures become noticeably warmer, heat stress has emerged as a critical concern in Singapore.

For the first time, the report sets out a special focus section on the illness, following the National Environment Agency's release of Singapore's first heat stress advisory last July.

Here are five key takeaways from the report.

Fourth warmest year on record

Temperature trends in 2023 highlight a consistent warming pattern in Singapore over recent years.

According to the report, last year’s annual mean temperature of 28.2°C tied for the fourth warmest year on record since 1929, along with 2015 and 1997.

Over the last decade — from 2014 to 2023 — Singapore experienced its highest mean temperature, 28.06°C, surpassing the previous record by 0.05°C.

This marked the third consecutive decade that has set a new high-temperature record.

The year began with cooler-than-average temperatures from January to March, attributed to La Nina conditions and increased northeasterly winds, with March being the coolest in the last decade.

However, from April, Singapore experienced warmer-than-average weather, with May recording the highest mean temperature of 29.5°C, 0.9°C above the long-term average.

October was exceptionally warm with a mean temperature of 29.0°C, surpassing the previous warmest October in 2002 by 0.3°C.

2024 expected to be warmer than 2023

Looking ahead, projections suggest that by mid-century, Singapore's 2023 temperature will be considered cooler than average, as days are expected to become hotter.

These projections were mapped out in the Centre for Climate Research Singapore’s third national climate change study, also known as V3, which was released in January.

All three of the study's projections on low, medium, and high emissions scenarios show varying temperature increases by the mid- and end-century.

Mid-century refers to the average over 2040-2059, while end-century refers to the average over 2080-2099.

By the end of the century, Singapore may face very hot days with temperatures exceeding 35°C for up to 351 days in a year.

Annual average daily mean temperatures are expected to rise to between 28.5°C and 32.9°C, and annual average daily maximum temperatures are projected to rise to between 31.9°C and 36.7°C.

High heat stress days

In 2023, Singapore faced 37 days of high heat stress, defined as when the hourly average Wet-Bulb Globe Temperature (WBGT) hits 33°C or higher.

WBGT, a global standard, accounts for various environmental factors, such as air temperature, humidity, wind speed and solar radiation, to provide a more accurate measurement of heat stress conditions.

These occurrences were most frequent in April, May, June, and October, with May recording the highest number of high heat stress days (10 days), followed by October (eight days).

In future projections, as highlighted in the V3 study, Singapore anticipates a significant increase in high heat stress days, with estimates of 75, 87, and 113 days on average by 2059 under low, moderate, and high emissions scenarios, respectively.

This marks a two to fourfold rise compared to 2023.

By 2099, the frequency of such sweltering days could soar to between 207 and 326 days on average under the high emissions scenario.

Studies have found that rising temperatures, extreme heat and high heat stress could lead to several adverse effects.

A recent study by the National University of Singapore (NUS) found that heat stress can cause lower fertility, worker productivity and cognitive capacity.

Exceptionally wet February and March

Last year, Singapore had its seventh wettest year since 1980, with a total rainfall of 2,866.1mm, which was 13.1 per cent above the long-term average.

February was exceptionally wet, with an islandwide average rainfall of 342mm. This was more than double the month’s long-term average of 132.1 mm, making it the fourth wettest February on record.

March also saw significant rainfall, ranking as the fifth wettest March since 1980.

The Met Service said while La Nina tends to bring wetter conditions, the wet start to the year was only partially due to this phenomenon.

This suggests that while La Nina contributed to the wet start to the year, other factors likely also contributed to the exceptionally high rainfall.

Other notable weather events

One of these factors is the rare late monsoon surge in late February and early March, labelled as a "notable weather event” in the report.

As a result, Singapore experienced widespread heavy rainfall, with all climate stations across the island recording over 100mm of rain, particularly in the eastern and southern parts of the island.

This rainfall broke records, with the highest daily total rainfall ever recorded in Kallang and Sengkang in February and March, respectively.

The monsoon surge also brought cooler temperatures to Singapore, with some days having maximum temperatures below 28°C, including a record-low temperature of 21.1°C recorded at Newton.

Another notable weather event was the hazy conditions and deteriorating air quality in October, with the highest 24-hour Pollutant Standards Index (PSI) recorded at 123. PSI readings from 101 to 200 are regarded as "unhealthy”.

This was due to an increase in hotspot and smoke haze activities, first observed in Kalimantan and later in Sumatra, Indonesia. ― TODAY