Singapore launches national heat stress advisory as world hots up

The readings, an average value over the past 15 minutes, will come from Wet Bulb Globe Temperature stations closest to the user’s location.

Joyce Teo and Sophia-Ines Klein

Joyce Teo and Sophia-Ines Klein

The Straits Times


There is a high likelihood that El Nino conditions, which are expected to bring warmer and drier weather, may develop in the second half of 2023. PHOTO: ST FILE

July 25, 2023

SINGAPORE – Singapore has released a national heat stress advisory to encourage people to look after their own heat health when engaging in prolonged outdoor activities, as the prospect of rising temperatures and more warm days ahead looms.

The heat stress level – indicated as low, moderate or high – is available on the myENV app and at, the Meteorological Service Singapore’s (MSS) website. The three tiers are colour-coded: red for high, amber for moderate and green for low.

The readings, an average value over the past 15 minutes, will come from Wet Bulb Globe Temperature (WBGT) stations closest to the user’s location. WBGT readings indicate how hot the human body feels, taking into account not just air temperature, but also humidity, wind speed and solar radiation.

The National Environment Agency (NEA), which has nine WBGT stations islandwide, uses their readings to gauge heat stress risk levels. Most stations are in sports stadiums, and more are expected to be established in the next two years.

Speaking to the media at the launch of the advisory at the MSS’ Central Forecast Office in Changi Airport on Monday, Minister for Sustainability and the Environment Grace Fu said the advisory offers a guide to what people can do to protect themselves against the heat in an increasingly warming world that brings extreme weather events.

“If you are just walking from your home to the bus stop, it is probably not necessary to follow,” she said. “If you are thinking about going out for a run or taking your family out for a picnic for some time, please check this information on myENV (app) before you make that decision to go.”

Ms Fu said the advisory is designed for the average person, which is why those whose elderly parents are suffering from medical conditions, or who have very young children, should take more care.

The heat stress advisory comes as El Nino is expected to return. The MSS has said that there is a high likelihood that El Nino conditions, which are expected to bring warmer and drier weather, may develop in the second half of 2023. The warming weather phenomenon last occurred in 2016, which was the hottest year on record globally and in Singapore.

Heat stress occurs when the body is unable to cool down effectively through the evaporation of sweat. The signs and symptoms to watch out for include headaches, nausea, dizziness, confusion and heavy sweating.

These can occur even in the absence of a heatwave, said NEA.

The heat stress advisory aims to minimise the risk of heat-related illnesses such as heat cramps, heat exhaustion or, in severe cases, heat stroke, which can be fatal, the agency said. Extreme heat can also affect people in other ways, as well as lead to hospitalisation.

One of the main components within the WBGT formula is the natural wet bulb temperature, which represents the effect of the humidity in the air, among other factors.

Higher humidity or atmospheric moisture content decreases sweat evaporation, making it harder for the human body to cool down. This leads to a higher wet bulb temperature, although this reading is mostly lower than the air temperature, said an MSS spokesman.

The wet bulb would be identical with the air temperature at 100 per cent relative humidity.

WBGT levels of 33 deg C or higher will expose people to a high level of heat stress, while a reading from 31 deg C to below 33 deg C indicates moderate heat stress. Anything below 31 deg C is considered to cause low heat stress.

The frequency and duration of moderate or high heat stress vary from month to month, said the MSS spokesman.

“The warmer months of April and May typically see high heat stress observed for about half the days in these months, with the period of high heat stress lasting for up to 1½ hours,” he said.

In contrast, during the cooler north-east monsoon months of November to February, high heat stress is observed only during a few days in a month, and for shorter durations of up to half an hour.

“On the days when we observe high heat stress, it usually occurs between the hours of 11am and 3pm,” he added.

Environmental heat stress is only one factor that can affect how hot a person can get.

Two other key factors are one’s attire and the activity that is being undertaken, said Associate Professor Jason Lee, director of the Heat Resilience and Performance Centre at the National University of Singapore’s Yong Loo Lin School of Medicine. “So, if a person does not change his attire and activity and the heat stress level increases, his health risk will increase accordingly,” he said.

The heat stress level – indicated as low, moderate or high – is available on the myENV app and at, the MSS website. ST PHOTO: JASON QUAH

Furthermore, not everyone reacts to heat in the same way.

Dr Ong Pei Yuin, a consultant in the Department of Emergency Medicine at the National University Hospital (NUH), said the risk factors for heat injuries are pre-existing illnesses, dehydration and extremes of age, such as the very young and the elderly.

Individuals with pre-existing medical conditions that decrease their immunity will find their body’s ability to cope with heat stress compromised, she said.

Young children whose body systems have not fully developed and older adults whose body systems are ageing and have decreased heart functions and body reserves will be less able to regulate heat, she added.

The NEA said people who are more vulnerable to heat stress should be more cautious.

The heat stress advisory is meant for the public as there are already separate guidelines for athletes, outdoor workers, students and Singapore Armed Forces personnel.

For instance, Singapore’s workplace safety and health guidelines on managing heat stress state that workers new to Singapore should be put on a heat acclimatisation programme, which gives them more rest breaks and closely monitors them for symptoms of heat injury.

NEA and the Ministry of Sustainability and the Environment developed the heat stress advisory, in consultation with the Ministry of Health’s (MOH) heat stress guidelines expert panel.

Scientists around the world have sounded the alarm on the extreme heat that El Nino, together with global warming, will bring. The World Meteorological Organisation has said that there is a 98 per cent likelihood that at least one of the next five years, and the five-year period as a whole, will be the warmest on record.

On May 13, Singapore logged an air temperature of 37 deg C in Ang Mo Kio, a level not seen since 1983.

Just last week, the World Health Organisation said it is collaborating with the World Meteorological Organisation to support countries in developing heat health action plans to coordinate preparedness and reduce the impacts of excessive heat on health.

Prof Lee, who sits on MOH’s heat stress guidelines expert panel, noted that Singaporeans, living in the tropics, complain about heat but never really consider that it can ever become too dangerous.

“We are like frogs being boiled slowly, not knowing we are being cooked. With this advisory, we want to first create awareness that the level of heat stress we are experiencing can be damaging in extreme cases,” he said.

The direct impact includes heat injuries, reduced work productivity and compromised decision-making, while the indirect impact would be the prolonged avoidance of outdoor exercise, he added.

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