How the Data Team measured heat stress in Chennai

The Hindu

17-07-2025

This article forms a part of the Data Point newsletter curated by The Hindu's Data team. To get the newsletter in your inbox, subscribe here
Welcome back, data enthusiasts!
Your experience of a 36°C day may not be the same as everyone's.
We at The Hindu Data Team have explored this concept in our latest interactive story titled: 'Taking on the heat.' The story covers the day-to-day experiences of four working class individuals across Chennai, with varying levels of exposure to direct sunlight. It details the respondents' heat management mechanisms and potential help they could receive for the same from the State.
Where our stories generally explore sociology, policy, and more via numbers, our approach for this story differed, as we combined originally sourced data, reportage, and interactive graphics.
The idea gained momentum when Dr. Srinivasan Ramani, deputy national editor at The Hindu, found inspiration in The New York Times' article 'Who Gets to Breathe Clean Air in New Delhi?' He noticed that they had taken recourse to a Raspberry-Pi Device along with air pollution monitors to build an interactive story, earlier in this decade, on differential impact of air pollution on two children from different class segments in New Delhi.
Knowing that Arduino-based devices cost much lower than a Raspberry-Pi mini-computer, Dr. Ramani along with hardware engineer Mr. Sanjeevi Maran procured and built this device for measuring heat stress in Chennai.
We scoured hobbyist/electronics sales' websites to buy the components for the device -- an Arduino Nano micro-controller, a DH22-temperature and humidity sensor, a data recorder/logger module, SD Card to store the data and batteries, all of which were to be fitted in a DIN case -- all of which cost us less than Rs 2,000 per device.
We asked our respondents to keep the devices on for 24 hours from 9 AM on June 9 to 9 AM on June 10. Once this data was collected, the Data team sifted through the datasets procured from the SD cards and calculated the respondents' heat index. The goal was to determine how much heat stress one is suffering, not just the air temperature.
Using this data, we gauged which parts of the day brought the most discomfort to our respondent. We spoke to them about their routines, which parts of the day were particularly unbearable and tried to understand the specificities of their experiences. Our photographers made sure to capture this visually. With the guidance of our Deputy Science Editor, Vasudevan Mukunth, we also consulted various experts on the subject of heat stress; its impact on the body, what amplifies it, how it can be reduced, and what is and is not being done about it.
Our principal correspondent, Vignesh Radhakrishnan, and our editorial coder, Areena Arora, concocted how to best put forth the subtle distinctions in their day-to-day lives.
We felt that loading the story with heat stress data on readers wouldn't have delivered the true impact of working in 60°C plus temperatures and we risked it reading like a scientific story. At the core of this project, while there is rich data collection and analysis, is a human, sociological aspect. Using intentional elements like a moving time counter, illustrated images and showing both real and heat index temperature really brought home the point - some professionals are exposed to dangerously high heat levels.
We collaborated with our National Design Editor, Kannan Sundar, for art direction and our Chief Illustrator, Soumyadip Sinha who brought our respondents' stories to life through his illustrations.
Click here to read the story.
What we published in the last two weeks
In the last three months, a string of dowry-related deaths have been reported from across India. We used numbers from the National Crime Records Bureau to understand how these cases are still prevalent in society and how their investigations are dealt with by the police.
Dowry deaths in India: Long investigations, rare convictions
Last Saturday, Animesh Kujur became India's fastest man by breaking the national record in the men's 100 metres, in under 10.20 seconds, clocking 10.18 at a meet in Greece. We looked at how this feat compares to past national records and how far India's sprinting benchmarks still are from global standards.
How fast is India's fastest man, Animesh Kujur? | Data
Custodial deaths continue across India, and especially in Tamil Nadu, without a single conviction between 2017–21. Despite hundreds of deaths and dozens of inquiries, zero custodial-death prosecutions succeeded in TN. We looked at the status of such cases in various States using data from the National Crime Records Bureau.
Custodial deaths: Police convictions remain zero in Tamil Nadu and beyond
Following the London-bound Air India plane crash in Ahmedabad, we took a look at the high number of fatalities and incidents involving Boeing aircrafts, and more airlines are opting for Airbus, Boeing's rival aircraft manufacturer.
Boeing faces headwinds from crashes and competition
Here are some important News in Numbers this week:
5.8
Number of infections averted by global vaccine reserves since 2000
In millions. Global stockpiles of vaccines under programmes supported by 'Gavi, the Vaccine Alliance,' helped prevent more than 327,000 deaths from outbreaks in low and middle-income countries since 2000, according to a new study. The alliance, established in 2000, funds the roll-out and scale-up of new vaccines through routine healthcare systems and preventive campaigns.
Source: PTI
33,000
Number of private sector jobs lost in the US in June 2025
According to the ADP chief economist Nela Richardson, layoffs remained rare, a slowdown in hiring and reluctance to replace departing workers led to job losses, particularly in professional services, education, and healthcare. Annual pay growth held steady at 4.4% for job stayers, while wage hikes for job switchers eased slightly to 6.8%.
Source: AFP
1,628
Number of cases of illegal transfer of tribal land to be probed by MH
More than 1,600 cases of the illegal transfer of tribal lands to non-tribal people have been identified for investigation in Maharashtra and a report will be submitted, Revenue Minister Chandrashekhar Bawankule told the legislative assembly on Wednesday. He stated that agricultural land can only be transferred to tribals, while non-agricultural transfers for commercial, industrial or residential purposes are subject to strict scrutiny under 34 conditions and Supreme Court guidelines.
Source: PTI