CHENNAI: Tamil Nadu released the state's first-ever block-level spatial analysis of heat exposure, on Monday. The decadal study, conducted by the Tamil Nadu State Land Use Research Board and State Planning Commission confirms that rising urbanisation and loss of natural land cover are driving a dangerous surge in local temperatures across the state.
Out of 389 development blocks, the study found that 94 have experienced significant decadal increases in heat stress, while 64 blocks are currently enduring higher-than-state-average temperatures, even if they haven't seen long-term trends.
Critically, 25 blocks which fall under 10 districts -- Chennai, Chengalpattu, Karur, Madurai, Pudukkottai, Ramanathapuram, Sivagangai, Tiruchy, Tirunelveli and Tiruvallur -- fall under the 'extremely heat-stressed' category in both assessments. The study found that many of the blocks that fall under both critical categories are associated with intensive urban development or proximity to industrial belts.
"These blocks are of particular concern as they represent areas where temperatures have both increased significantly over time and are currently above the state average, indicating persistent and intensifying thermal stress," the report states.
The findings draw a direct link between land use change -- especially built-up area expansion -- and temperature rise. For instance, Chennai's built-up area grew from 48% of its total area in 1985 to 74% in 2015. St. Thomas Mount in Chengalpattu district saw a staggering fivefold increase in built-up footprint, surpassing even the capital in relative growth. In these urban and peri-urban zones, temperatures have risen by up to 2 degree Celsius above the state average in just two decades.
J Jeyaranjan, Executive Vice Chairman of State Planning Commission, said Tamil Nadu is witnessing rapid urbanisation and economic growth, but this progress comes with significant climate challenges. "This study provides critical insights into how urban expansion and land use changes affect local climate conditions at the block level. Such research is essential for ensuring that policies are backed by data and that development remains sustainable. Moving forward, the integration of climate data into land use planning, enforcement of urban regulations, and increased investments in green and blue infrastructure must be prioritised."
One of the study's key insights is the growing severity of night-time land surface temperatures (LST) -- a metric linked to heat retention and human discomfort. Between 2000-2005 and 2018-2023, night-time LST rose by nearly 4 degree Celsius in major urban centres like Chennai, Salem, Coimbatore and Tiruchi. Across the state, average night-time LST increased by 2 degree Celsius, indicating widespread thermal stress.
The combined effect of reduced vegetation and increased impervious surfaces like concrete has amplified the urban heat island (UHI) effect, particularly in fast-expanding zones and ecologically sensitive hilly terrain.
With thermal discomfort days projected to increase from 107 to 150 days per year by 2050, the report warns that urban heat is becoming a major public health and infrastructure risk. "This is not a future problem -- it's happening now. And unless we adapt at the micro level, block by block, we will see cascading impacts on agriculture, health, water security, and the economy," the report states.
The report recommends a multipronged approach, including integrating thermal data into local planning, enforcing climate-sensitive building codes, and investing in nature-based solutions like blue-green infrastructure and urban forests.
A separate report titled 'Framework for Nature-based Solution (NbS) for enhancing Urban Resilience in Tier 2 cities' also by the State Planning Commission, highlights the potential of NbS to reduce disaster risks, improve urban liveability and restore ecosystem services. It also touches upon the importance of early intervention in Tier 2 cities to avoid unsustainable development.