In 2024 Chennai has recorded close to 120 days of the temperature crossing 35°C. That is four of the nine months of the year so far! If the high relative humidity is also factored in, the number of days that would have “felt like” more than 35°C would be much higher.

What does this mean for people working in economic centres like Koyambedu? What would it mean for people living next to large landfills? How will the Waste-To-Energy plant planned to come up in Kodungaiyur exacerbate this situation? How are people living in informal settlements affected by urban heat? These are some of the questions the participants at the day-long datajam on “Urban Heat in Chennai” tried to answer.

Urban Heat in Chennai

The datajam was conducted in partnership with C40 Cities, CAG Chennai, Reach the Unreached and Poovulagin Nanbargal, and was facilitated by Armaan RM, an independent GIS Specialist. The event was conducted in DLF IT Park near Manapakkam, facilitated by Naren Sundram of Sagent M&C India Pvt Ltd.

In the all-day event, 32 participants from diverse backgrounds – GIS experts, developers, architects, students of planning from Anna University, social workers and people who work at the ground level – looked at six wards using satellite data, both current as well as historic to understand how the city of Chennai has changed in the last 10 years, how these changes have manifested in terms of changes in built-up area, green cover and how these changes have driven the heat stress in the city.

Problem Statements

Similar to the “Addressing Urban Heat in Bengaluru” datajam, the participants chose a ward each with different characteristics to understand the effect of Urban Heat in different contexts. The wards chosen and their profile were:

1. Perungudi – 189: Presence of a large landfill as well as the Pallikaranai marshland which has seen a lot of encroachment with a sudden spurt in development around it in the last couple of decades.
2. Triplicane – 114: One of the oldest areas in Chennai with a high density of commercial areas as well as built-up areas, while also being next to the sea.
3. Villivakkam – 94: An industrial area with a SIDCO in it, the industries have slowly moved towards Ambattur and Sri Perumbudur to be closer to the larger automobile industries.
4. Kodungaiyur – 37: Presence of a large landfill with a planned Waste-To-Energy plant. Situated in North Chennai it also has a large number of informal settlements around it.
5. Tondiarpet – 41: Presence of a large number of informal settlements as well as the Kodungaiyur landfill next to it.
6. Koyambedu – 127: The Koyambedu market employs a large number of people, while the CMBT sees the movement of a large number of vehicles as well as people on a daily basis.

Outputs

Perungudi – 189

The team comprising Manikandan, Glory, Poiyamozhi, Sangeetha Priya and Yaazhini aimed to identify the heat risk in Perungudi ward and also understand how the growing size of the landfill has contributed to it.

They noted that the area has grown from a small village to a thriving residential and commercial hub mainly due to the boom in the IT sector in the past two decades. It is also home to one of the Chennai’s largest landfills which has caused both air and water pollution spilling into the Pallikaranai marshland and leaching into the groundwater. The marshland itself has shrunk to close to 10% of its original size.

While LST data shows that the temperature of the landfill itself has increased and the area of the hotspot has also increased, the change in built-up area has also resulted in increased temperature in the rest of the ward.

Triplicane – 114

Avinash, Bharat, Divya, Nishalini, Shiva Subramaniam, Shruthi and Thanigavel looked at the changes in Triplicane over the last 10 years and how they have contributed to the urban heat profile of the ward.

They noted that Triplicane is one of the oldest areas in Chennai, known for its rich cultural heritage and organic development. However, in recent times the area faces significant commercialisation and population growth leading to reduced residential spaces and green areas.

The team looked at the changes in LST data between 2013 and 2023 and noted that while loss of green cover has led to increased temperatures in the internal parts, changes in the ocean temperature have also led to increases in the parts abutting the sea.

They noted that the green cover in the area has been significantly affected by events like cyclones which have felled many trees because of the proximity to the ocean.

Villivakkam – 94

The team comprising Arvind Roshan, Nitish, Sumeet, Swaminaatha and Vishwa Adithyan looked at how the presence of a SIDCO industrial estate can affect the heat characteristics of a ward. What they found was surprising and led them to make more investigations.

Looking at changes in LST data between 2013 and 2023 they found that the temperature in many areas of the ward had actually decreased by 4°C. However, in general they found that residential areas are generating more heat than non-residential areas.

They noted that rising land costs and presence of larger industries near Ambattur and Sri Perumbudur might have made the industries in the SIDCO estate relocate to Ambattur and other areas. That area has been taken over by the Tamil Nadu Housing Board. They found that the thermal profile of the TNHB area is much higher than surroundings which could be because of denser construction with little space between blocks.

Kodungaiyur – 37

Kodungaiyur in North Chennai is home to one of the largest landfills in Chennai. Anusuya, Dalip, Kamali, Rethika and Shiny looked at how waste-to-energy plants can affect the areas surrounding them.

The Kodungaiyur landfill already records a peak temperature of 50°C on extremely hot days which is not only much higher than its surroundings, but also despite the marshland next to it. Having a WTE plant here could raise the temperatures of the surroundings as seen in the case of the WTE plant in Pune which became operational in 2008 and caused a very visible increase in heat in the surrounding areas.

Tondiarpet – 41

Team comprising Afrah, Jenny, Lokesh, Mukesh and Senthil analysed the heat impact on Tondiarpet, an area in Northern Chennai with a large number of informal settlements.

They noted that Tondiarpet and surrounding wards have a large presence of people from SC and ST communities – more than 20% suggesting a vulnerable socio-economic profile. Even though most of the houses have concrete roofs, more than 20% of the houses have asbestos roofing suggesting a direct correlation with the caste profile of the wards.

Comparing the LST data between 2013 and 2023 they noted the massive increase in land surface temperatures due to the presence of the neighbouring Kodungaiyur landfill as well as an increase in temperatures in areas with informal settlements.

Koyambedu – 127

Ammar, Azeera, Mokshavathi, Prabhu and Sakthivel looked at the impact of heat on the urban space of Koyambedu. They noted that while the area was relatively undeveloped in 1980, it is now a well developed area with major landmarks like a Metro station, the CMBT bus stand and the Koyambedu market.

Not coincidentally, they found that these landmarks are also thermal hotpots, with the median temperature going over 45°C on hot summer days. While the metro is expected to reduce private vehicle usage, the station was seen to be a heat hotspot which was hard to explain.

They also noted the absence of public toilets with just 96 functioning ones and 10 more proposed to address the needs of 3600 vendors and more who work there.

Conclusions

Chennai has two major landfills – at Perungudi and Kodungaiyur. The two teams who analysed the heat stress in both these wards found clear evidence that the landfills were contributing to extreme heat in the area, to the effect of more than 10°C in comparison with the surroundings. The team that analysed Kodungaiyur noted how the Waste-To-Energy plant will make it even worse if it comes up.

Chennai being a coastal city is expected to be cooled by the ocean currents, but the team that analyzed Triplicane found that the ocean has also warmed up in the past 10 years. This can have deleterious effects on coastal and fishing communities.

One of the teams noted that a SIDCO industrial estate relocating further away reduced the temperature in the area by 4°C, but such relocations cannot be done everywhere, and replacing the area with highly dense housing board constructions squandered away the advantages.

All the teams noted that presence of waterbodies as well as green areas helped bring down the temperature. While Koyambedu bus stop was a major heat hotspot one of the teams found that the neighbouring wooded area was a markedly cooler region in the ward.

The effect of cyclones bringing down trees was felt in Triplicane where the temperature was seen to have gone up in areas where the trees had been brought down.

All teams noted the lack of green cover, dense constructions with little breathing space were contributing to heat stress. Green cover, access to cool roofs and better roofing materials were recommended as the needs of the hour.

For the participants, the event was a learning experience to look at practical aspects of data as well as heat resilience. As Shruthi M, a participant put it, ” we are enriched with the data available and have gained the ability to manipulate the data with our study. Also, it was great to meet people from multidisciplinary aspects and their expertise.”

Armaan RM, a researcher who helped facilitate the datajam noted that “the concept of a datajam is at the heart of citizen science and data science, wherein citizens use data to foster transparency and make data available. It’s great seeing people from different backgrounds coming together to tackle larger problems such as climate change.”

Manikandan M of the CAG felt that events like the DataJam on Urban heat island “is really the need of the hour in major cities. It provides an opportunity to the participants to analyse and find the insights of public data.”

According to Karthik G of C40 Cities, “urban heat is the silent killer sweeping urban centres across the globe. With ever increasing concretisation, reducing green spaces, depleting water bodies combined with increasing global temperatures, vulnerable communities face an uphill battle for survival. Datajams like this one are a great opportunity for professionals from different disciplines to come together to understand and collaborate with each other and work towards a solutions.”

Jenny of Poovulagin Nanbargal summed up the issues facing our cities. “Heat is becoming a major threat given climate change, drastic land use changes and is only going to get worse, especially for the vulnerable people who are facing its brunt. By mapping land use and other changes over the years, we can gain insights into the factors exacerbating heat impacts, particularly in conjunction with urbanisation. Data-driven approach is vital for informing sound policy decisions and fostering government action. Transparent and easily accessible datasets are key to ensuring effective, evidence-based interventions. I believe events like this play an important role in advancing our understanding and response to the growing challenges posed by heatwaves.”