During mid-winter in New Zealand, it may be hard to imagine extreme heat. But for several weeks during their summer months, millions of people in the US, Europe, China and India have endured record-shattering temperatures, often spiking well above 40°C.
Working or even just being outside in such scorching heat is dangerous, even deadly, especially if nights stay hot as well. For many, not even their homes provide shelter to cool. “Heat exposure beyond what human physiology can tolerate is becoming a huge issue globally,” says Aditi Bunker at the University of Auckland’s Centre for Pacific and Global Health, who co-leads a project with Sir Collin Tukuitonga to trial cool-roof technology in several countries, including Niue.
The project extends Bunker’s earlier research in rural Burkina Faso in west Africa to four global urban climate hotspots, including urban Burkina Faso, Niue, Mexico and India. It involves painting roofs with an inexpensive, non-toxic coating that reflects the sun’s energy and minimises heat uptake. “The countries we focus on are limited in resources but likely to experience prolonged periods of heat,” she says. “The cool-roof coating is highly reflective and has high thermal emittance, which together reduce indoor temperature passively, without high energy demand.”
The body’s primary response to heat is to sweat, but extreme conditions can overwhelm the heart as it pumps harder to bring more blood from the body’s core to the periphery to dissipate heat. Sweating becomes ineffective when high temperatures combine with high humidity.
Prolonged day-and-night exposure to extreme heat can have devastating impacts on people’s health “because the body doesn’t get the respite it needs at night to recover and replenish”.
Physical health impacts range from dehydration to heat stroke, and ultimately the collapse of the body’s heat-regulating functions, but extreme heat also affects people’s sleep patterns and mental health.
Bunker’s project is part of an international collaboration to develop passive home-cooling technologies. It includes researchers in each country working in partnership with companies that sponsor and manufacture the cool-roof coatings. But the first and most important step is to get communities on board.
She is visiting Niue this month to meet local leaders and citizens to hear about their perceptions of climate change and the current ways people are adapting to the heat. “If we engage with local people, it becomes a project that’s driven by the community. It’s very much a participatory approach to the work.”
The next phase focuses on gathering data about the technology from a few households that are equipped with a comprehensive sensor system, measuring the temperature directly on and under the coated roof, as well as temperature and humidity outside and inside the home. Roof reflectivity will also be measured, and the team will collect energy bills to find out if people save on costs and reduce emissions.
The final phase is a comprehensive, randomised trial in a minimum of 400 homes at each site, in which equal numbers of homes receive cool-roof coatings or keep their conventional roof. “We then gather objective and subjective measures to look at the health impacts on people and what it means for their wellbeing and comfort,” Bunker says.
Smart devices will measure people’s body temperature, heart rate, blood pressure, activity and sleep patterns, which can all be indicators of heat stress. Surveys will provide a more subjective measure of how people cope.
The project is one of nine funded globally by the Wellcome Trust with the aim of testing adaptations to prevent heat-related illnesses and deaths. The projects were selected to have immediate benefits for communities already exposed to heatwaves and to produce evidence that can be used by governments, donors and policymakers.
Bunker says if the cool-roof research identifies benefits, all homes in the trial will get the technology.
