Heat‑Index Maps Reveal When Urban Greening Cuts Temperatures – and When It May Backfire
Researchers at the Indian Institute of Technology Gandhinagar (IIT‑GN) have released a detailed heat‑index mapping of several Indian cities that shows precisely where tree‑based greening most effectively reduces ambient temperatures and where it can unintentionally raise heat stress. The study, published in the journal *Environmental Research Letters* on 10 May 2026, analysed satellite‑derived land‑surface temperature data and on‑ground heat‑stress measurements for over 150 neighbourhoods across Delhi, Mumbai, Chennai and Kolkata. The authors found that strategically placed street‑level canopy can lower the heat‑index by up to 5 °C during peak summer, but in densely built‑up blocks with poor ventilation the same trees sometimes trap heat, raising the index by as much as 2 °C.
Urban heat islands have become a central concern for Indian municipal governments, which have pledged to plant 100 million trees by 2030 under the National Greening Initiative. While greening is widely touted as a low‑cost climate‑adaptation tool, city planners have struggled to predict which streets will benefit most. This new mapping effort fills that gap by coupling high‑resolution thermal imagery with wind‑flow models, offering a city‑wide “cooling potential” score for each block. The work matters because heat‑related mortality in India has risen 30 % over the past decade, and reliable mitigation strategies are urgently needed.
The IIT‑GN team, led by Professor Anurag Kumar, reported that streets with a canopy cover of at least 30 % and a width‑to‑height ratio greater than 4:1 experienced the greatest temperature drops. Conversely, narrow alleys (<5 m wide) with dense foliage saw heat‑index increases due to reduced airflow. “Our results highlight that greening is not a one‑size‑fits‑all solution,” Kumar told Phys.org. Co‑author Dr Meera Sharma added, “City officials should prioritize planting in corridors that already have good ventilation, and consider alternative cooling measures—like reflective pavement—in tightly packed zones.” The paper cites a parallel study by the Indian Meteorological Department, which reported similar backfire effects in Old Delhi’s historic lanes.
Urban‑climate experts say the findings could reshape India’s heat‑action plans. “This is the first time we have a quantitative, location‑specific guide,” noted Dr Rohit Banerjee, a climate‑risk analyst at the World Bank. He warned that without integrating these maps, municipalities risk misallocating resources, potentially exacerbating heat stress for vulnerable populations. Environmental NGOs have welcomed the research, urging city councils to incorporate the tool into their next urban‑development drafts.
The research team plans to update the heat‑index maps annually and make the data publicly accessible through an interactive web portal by early 2027. Municipalities are expected to submit greening proposals that align with the new cooling‑potential scores during the upcoming fiscal planning cycle. Stakeholders will be watching for the Ministry of Housing and Urban Affairs’ guidance on how the maps will be embedded in the National Urban Heat Management Framework, slated for release later this year.