Consecutive hot nights pose a higher risk to public health than hot days, and bring a 6 per cent higher risk of death for women and the elderly, a study by a Hong Kong university has found.
The findings came after the Observatory said earlier this month that July was the hottest month the city has experienced since record-keeping began in 1884.
Last month also saw a record 20 “very hot days” and 21 “hot nights”. Very hot days are defined by a maximum daily temperatures of 33 degrees Celsius or more, while hot nights are defined as having a temperature that does not drop below 28 degrees.
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“Our study found hot nights increased the risk of death by about 2 to 3 per cent, while a prolonged period of five or more hot nights raised the risk to 6.66 per cent,” said Dr Kevin Lau Ka-lun, a research assistant professor at Chinese University’s Institute of Future Cities.
A continuous period of five or more very hot days raised the risk of death to about 4 per cent, Lau’s study found.
“This shows that hot nights have a larger impact on the mortality risk, while women and elderly face a higher risk of dying from five consecutive hot nights,” Lau said. Women were 6 per cent more at risk of death from hot weather, while elderly people were 5 per cent more at risk.
Lau, who co-led the study with fellow research assistant professor Dr Shi Yuan and the University of Hong Kong’s Dr Ren Chao, compared temperature records from the Observatory and data released by the Hospital Authority over a period of 10 years from 2006 to 2015 to reach their conclusion.
“Nighttime is supposed to provide the body with a chance to recover and rest from the heat of the day, but ‘hot nights’ make the recovery and resting less effective,” Lau said. Women also tend to have a higher proportion of body fat, which makes them more susceptible to heat.
Ren said the health impact of hot weather was cumulative, which meant heat would place even more stress on the bodies of the elderly, particularly those with terminal or long-term illnesses. Heatstroke also had negative effects on the brain, kidney and liver, she said.
The researchers said climate change was the main factor contributing to the increase in hot weather in the city, while data from the Observatory shows that the annual number of hot nights could reach as high as 80 between 2051 and 2060, and almost double that by the end of this century.
“Hong Kong already has an ageing population, so it is highly likely the mortality risk from hot weather will be higher in the future,” Ren said.
Residents who live in cramped subdivided housing with bad ventilation were already suffering disproportionately during hot spells, she added.
But Ren said the effects of high temperatures could easily be mitigated with smart urban planning.
A separate study by Ren and Shi looking at the distribution of hot nights and days across Hong Kong found that more built-up areas, such as Mong Kok, Central and Causeway Bay, had more hot nights, while the New Territories had more very hot days. This could be due to the high density of buildings in urban areas, which trapped heat within the city, Ren said.
Based on their study, Ren suggested housing designs that allowed for better ventilation by taking into account wind direction, along with more greenery and open spaces.
“Hong Kong absolutely has the space to improve on its urban planning and design, and we hope the government can integrate designs that allow for more ventilation into city planning,” Ren said.
Meanwhile, Lau said residents should have a higher awareness of hot nights and take appropriate measures to lower their body heat, such as by taking showers and drinking more water.