For heat warnings to work, Hong Kong must have one clear, integrated system

On the hottest day of the year, three different warnings were in force, having come on at different times – an integrated system would more clearly communicate the risk
Besides policy and supportive employers, public awareness and education is also important as temperatures continue to rise with climate change

Emily Ying Yang Chan,Holly LamandJanice Ho

Published: 8:15am, 10 Jun 2023

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Hong Kong’s new heating stress warning system for workers, introduced by the Labour Department last month, is a good start to the city’s management of health emergencies and disaster risks from climate change. This comes as research shows strong associations among temperature, morbidity and mortality in Hong Kong.

The warning system uses as the benchmark the Hong Kong Heat Index, which takes into account temperature, humidity, wind speed and sun radiation.

But what should be tackled is how to integrate this new system with the Hong Kong Observatory’s existing hot-weather warnings to simplify the city’s health disaster warning system for heat risks. There have been successful examples in the use of typhoon and rainstorm warning systems for workers.

One of the article contributors, Emily Chan, collaborated with the Observatory to research and develop its heat index in 2014, using hospitalisation and heat stress data from 2007 to 2011 to assess the health impact of high temperatures, high humidity, slow winds and strong sun radiation. That same year, the Observatory introduced the two-tier hot weather warning.

Tier 1 is triggered by a heat index of 29.5 with Tier 2 warnings in place when the heat index hits 30.5. These thresholds are scientifically based – at 29.5, the excess hospitalisation ratio starts to pick up, increasing more rapidly after 30 and, by 30.5, reaches an alarming level.

The earlier warning gives the public a reasonable lead time to protect themselves from the increased health risks of heat stress.

In contrast, the new three-tier Heat Stress at Work Warning has thresholds for amber, red and black set at heat index readings of 30, 32 and 34 – which look too conservative. This is particularly because outdoor workers are much more exposed to weather than the general population.

On May 22, when the Observatory issued its Tier 2 “very hot weather” warning to the public, the Labour Department did not put up even the lowest amber warning for heat stress at work.

On May 30, the hottest day of the year, the amber alert was issued almost 30 hours after the “very hot weather” warning was in force, and 45 minutes after the Observatory issued for the first time an alert under its newly introduced “special weather tips” for when temperatures reach 35 degrees Celsius.

Greater transparency on the scientific basis of the new warning system for heat stress at work could improve people’s understanding of the alerts and their efficiency. Moreover, having two such similar warning systems can confuse the public. Given that simplicity and clarity are important in risk communication, the integration of these two systems should be explored.

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Moreover, unlike the straightforward work guidelines under typhoon and rainstorm warnings, such guidelines under the new warning system are very complicated. The frontline challenges in policy implementation and the difficulties in effectively communicating the health risks of heat stress to the community should not be underestimated.

Besides having the right policies, supportive work contexts and employers, raising public awareness of the health risks of heat, the responses they can take to extreme temperature warnings, and empowering people to take care of themselves via community education are equally important.

It takes coordination and planning for a warning system to work, and concerted efforts are crucial to ensure health protection objectives are met.

End confusion over Hong Kong workers’ heat alerts

In addition to protecting outdoor workers, we should also be concerned about schoolchildren having physical education outdoors in the hot summer, pregnant women, older people and those living in suboptimal conditions, like subdivided units, who might be overexposed to extreme temperatures.

Compared to adults, children are more efficient at heat production and less efficient at sweating, and so adapt to changes in temperature more slowly. Importantly, children are more likely to become dehydrated as they can lose fluids quickly and don’t have the awareness to adequately hydrate.

The elderly are also vulnerable to extreme temperatures as ageing affects the body’s ability to regulate temperature, leading to a decrease in the dissipation of heat.

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Research has shown that the very old and those with non-communicable diseases are at a higher risk of adverse health outcomes, including cardiovascular and respiratory diseases and accidental injuries. In the hot season in Hong Kong, every 1 degree Celsius increase above 29 degrees (the daily mean temperature) was associated with a 4.5 per cent jump in all hospital admissions and a 1.9 per cent increase in admissions for unintentional injuries.

The number of respiratory admissions among children (for example, those with asthma) and infection disease admissions for the elderly (e.g. for pneumonia) started increasing when the temperature rose above the same threshold.

The risk of heart-attack admissions among patients with type 2 diabetes also increased when temperature rose over 28.8 degrees, highlighting the vulnerability of those with pre-existing conditions. These health effects will worsen with more frequent and severe extreme temperature hazards as a result of climate change.

As Hong Kong works to mitigate the impact of climate change, whether extreme temperatures, rising sea levels or more frequent and stronger typhoon and storm surges, government policies should not deviate from science and rationality, or ignore disaster risk reduction for the sake of economic activity, when Beijing emphasises high-quality development.

Emily Ying Yang Chan is co-director of the Collaborating Centre for Oxford University and Chinese University of Hong Kong for Disaster and Medical Humanitarian Response (CCOUC), and the assistant dean of CUHK Faculty of Medicine

Holly Ching Yu Lam is an adjunct assistant professor at CCOUC. Janice Ying En Ho is a postdoctoral fellow (honorary) of CCOUC. Chi Shing Wong also contributed to this article

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