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Commentary: Singapore’s heat stress advisory signals a hotter world to come

SINGAPORE: As record-breaking temperatures make headlines globally, Singapore is taking action to manage heat risk. In July, the government launched a new advisory that provides the public with real-time information and advice on the risks of heat stress.

Living in a tropical, highly urbanised city, Singaporeans contend with high temperatures and humidity year-round. Yet Singapore has not been spared from “global boiling”, with temperatures hitting 37 degrees Celsius for the first time in decades this May. Hot conditions are expected as El Nino takes full effect.

Singapore’s heat stress advisory uses a measure of heat called the Wet Bulb Globe Temperature (WBGT). Besides temperature, it accounts for the effects of humidity, solar radiation and wind, providing a more accurate measure of what conditions actually feel like and their potential health risks.

Humidity, in particular, is often what makes heat unbearable. Even moderate temperatures, combined with high humidity, can be dangerous for humans. In tropical climates like Singapore, heat and humidity pose an everyday risk, so measuring WBGT, rather than just temperature alone, is essential.

Because the WBGT assumes full sun exposure, the advisory is aimed at managing outdoor physical activity. Traditionally, the WBGT has been used to estimate the impact of heat on outdoor workers, athletes and military personnel, and these groups already have their own heat risk plans in place.

For the public, the heat stress advisory provides broad advice on when prolonged physical activity might be dangerous and how to manage risk by exercising later in the day, staying hydrated or wearing lightweight clothing. This may be common-sense advice but it is nonetheless important in raising awareness as hot days become more frequent.

However, what good would a heat stress advisory be if Singapore sees WBGT crossing into high-risk thresholds on a regular basis? Education will be key to safely adapt to warmer weather, but care must be taken in warning the public too frequently and in non-specific ways, so as not to lead to complacency.

KNOWING YOUR LOCAL RISK

WBGT is currently measured at nine stations across Singapore, with readings updated every 15 minutes. This allows Singaporeans to check their real-time heat risk from the station closest to them.

This localised information is welcome, but still lacking granularity. Within a given town or region, heat risk varies quite substantially. Temperatures tend to be hotter in more urbanised areas, known as the urban heat island effect. Conversely, areas with high vegetation can be cooler because plants provide cooling via shade and evapotranspiration.

With only nine stations, these nuances are currently lost, an issue that will be addressed over the next two years as the network of stations is set to expand. With more granularity, the heat advisory can help urban planners visualise the benefits of green spaces across the island. Developing these green spaces is important for people’s physical and mental health, as well as for providing much needed cooling.

A next step could be to provide heat stress information alongside weather forecasts, so that we can plan ahead for high heat-risk days. Temperature forecasts are already common. But because other factors like humidity and solar radiation are critical to estimating heat stress, these need to be predicted reliably, a challenge that is still very much a frontier of science.

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