Carbon dioxide sensors on top of the Opéra Bastille building in Paris will help to measure atmospheric emissions in the city.Credit: Pekka Pelkonen/ICOS RI
In 1950, only around one in five people lived in a city. Now, that figure is close to one in two. Thirty-three of these urban centres have achieved megacity status, meaning they are home to more than 10 million people. One of the largest — Tokyo, which has more than 33 million residents — is a behemoth of modern technology. Its major train station in Shinjuku is the world’s busiest, with an average of 2.7 million people passing through it every day.
Such a large city ecosystem cannot be studied at a single glance, whether it be from space or at street level. Understanding its inhabitants and how it functions requires scientific instruments that can capture changes over time and in several dimensions and locations, from subterranean structures to the noisy, polluted streets and the skies above. Here are four innovative scientific initiatives that are using sensors to explore how the constantly shifting cityscape affects the creatures it was created for: people.
Beating the heat
Summers in Ahmedabad are hot. In this city of more than nine million people, in the western Indian state of Gujarat, average temperatures in May hover at around 40 °C. This is well above what is deemed comfortable, and approaches levels that are dangerous for humans to live in. Those in the tightly clustered slums of the city are particularly vulnerable, inadequately protected from the heat by poorly built housing that is not well maintained.
Nature Spotlight: Sensors
The solution could be as simple as a coat of paint on the roof. Solar reflective paints have already been shown to reduce daytime indoor air temperatures by up to 2.7 °C (see go.nature.com/3t8mjq2). So, in 2023, an international study was launched to investigate the benefits of this low-cost approach, using a range of sensors to track the health outcomes of a group of residents in Ahmedabad, as well as people in locations in Burkina Faso, Mexico and the Pacific island of Niue. “What we are trying to see is the effect of intervention primarily on the health,” says Abhiyant Tiwari, the health and climate resilience lead at the National Resources Defence Council India, based in New Delhi, who is one of the investigators working on the trial.
Participating households have been equipped with an indoor thermometer to measure the direct effect on temperature, and one occupant in each residence has been given a smartwatch to track the physical effects of heat on heart rate, sleep patterns and activity levels. Heat exposure has significant health consequences, especially for young children and older people, as well as people with chronic health conditions, such as heart disease. This can be particularly severe during heatwaves in which hotter nights prevent the body from cooling down during rest. Globally, heat-related deaths in adults aged older than 65 years more than doubled between 1990–99 and 2014–23 (see go.nature.com/4butmft).
Reflective paint helps to keep buildings cool in Ahmedabad, India.Credit: Ajit Solanki/AP Photo/Alamy
“The other outcome would be to also understand how such interventions don’t just benefit people’s health, but also improve their productivity and reduce their energy demand for cooling,” Tiwari says.
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