The Hong Kong Observatory has recorded 36.9°C — the highest temperature measured in the city since records began in 1884.

To a reader in a hot country, 36.9°C may not sound remarkable. What makes it dangerous is not the number on its own.

How the body cools itself

Humans shed heat mainly by sweating. Sweat evaporates from the skin, and evaporation carries heat away. It is an efficient system with one requirement: the surrounding air must be able to absorb the moisture.

In humid air, it cannot. Sweat forms and sits there. The cooling mechanism runs without working, losing water and salt while body temperature continues to climb.

This is why humidity matters at least as much as temperature, and why a humid coastal city at 37°C can be more dangerous than a dry inland one at 45°C. Hong Kong is humid.

Why nights decide the outcome

The measure that best predicts heat deaths is not the daytime peak. It is whether the temperature falls overnight.

The body tolerates a hot day if it can recover during a cooler night. When night-time temperatures stay high — as they do in dense cities, where concrete and asphalt release stored heat after dark — there is no recovery period, and the strain accumulates across consecutive days.

That is also why the death toll of a heatwave typically rises towards its end rather than at its peak.

Who is actually at risk

Heat does not affect everyone equally, and the pattern is consistent across countries.

Older people are at greater risk: the sense of thirst weakens with age, and several common medications affect the body’s ability to regulate temperature. Infants have a limited capacity to cool themselves and cannot say what is wrong. People with heart, lung or kidney conditions face additional strain, because cooling requires the circulatory system to work harder.

Then there are the circumstantial risks: outdoor workers, people in housing without ventilation, and anyone who cannot afford to run cooling even where it exists.

Heat deaths are also frequently recorded under other causes — a heart attack, a stroke, kidney failure — which is why the real toll of a heatwave is usually established weeks later through excess-mortality analysis rather than in the news at the time.

Why a record in Hong Kong is notable

A record set against 142 years of continuous observation carries more weight than a record in a place that started measuring recently. The longer the series, the harder it is to explain an extreme as a quirk of the record-keeping.

Hong Kong is also a city built vertically and densely, with limited green space in its most populated districts — conditions that intensify heat rather than moderate it.

Anyone with a health condition affected by heat, or caring for someone who has one, should follow local health advice and speak to a doctor about their own situation rather than relying on general guidance.

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Source: Hong Kong Observatory, via AFP and Malay Mail, 9 August 2026.