Shade Is Infrastructure: How Nature Can Cool and Clean South Asia's Cities

Delhi has two seasons it dreads. In winter, it's the smog. In summer, it's the heat that won't let go, even at night.

New Delhi has now been the world's most polluted capital for eight years in a row. IQAir's 2025 World Air Quality Report puts its annual PM2.5 average at 82.2 µg/m³, more than 16 times the WHO guideline of 5 µg/m³. In summer, the Centre for Science and Environment (CSE) found that Delhi's core cools 3.8°C less at night than its peri-urban fringe.

We treat these as separate crises, run by separate departments. They aren't. And one of the best tools for tackling both is also the oldest: nature.

Two crises that feed each other

The urban heat island (UHI) effect happens when concrete, asphalt and dark roofs soak up heat by day and release it at night, with waste heat from vehicles and air-conditioners adding to it. In Delhi, CSE found that built-up area grew from 31.4% of the city in 2003 to 38.2% in 2022. The day-to-night cooling of land surfaces has fallen by 9% compared with 2001–10.

Heat and air pollution make each other worse. Ground-level ozone forms faster in hot, sunny conditions. Hotter cities run more air-conditioners, and UNEP projects that energy demand for space cooling could triple between 2016 and 2050. In winter, North Indian cities face the opposite problem: cold, still air traps particulates close to the ground.

The health stakes are huge. WHO estimates that outdoor air pollution caused 4.2 million premature deaths worldwide in 2019, and 99% of the world's population lived where air quality did not meet WHO guidelines. The burden falls hardest on outdoor workers, informal settlements and the elderly, who have the least access to cooling or clean indoor air.

What we mean by nature-based solutions

IUCN defines nature-based solutions (NbS) as “actions to protect, sustainably manage and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits.” Its Global Standard for NbS sets out eight criteria that help tell real NbS apart from tokenistic planting.

Saplings that die within two summers are not NbS. A restored, native, maintained and measured ecosystem is.

The NbS menu: what works for heat and air, and the catch with each

• Urban forests and Miyawaki-style plantations. Dense, multi-layered native forests shade the ground and cool the air through evapotranspiration. UNEP's cooling handbook cites US EPA estimates that tree groves can be 5°C cooler than nearby unshaded ground, and leaves catch particulates. The catch: dense micro-forests need water and care in their early years, and success should be judged by survival and canopy, not by the number of saplings planted.
• Street trees and green corridors. Continuous shade along roads and drains cools the places where people actually walk, wait and work. The catch: in narrow “street canyons”, tall, dense canopies can slow ventilation and trap traffic fumes. A review in Atmospheric Environment (Abhijith et al., 2017) recommends low hedges between traffic and footpaths, wider spacing between trees and well-ventilated canopy designs.
• Green roofs and walls. These cut heat gain in buildings; UNEP notes green roofs can reduce building energy use by 10–15%. Their effect on city-wide air quality is modest, and they need structural checks and upkeep.
• Urban wetlands, lakes and blue-green infrastructure. Water bodies and vegetated drains cool the air around them, recharge groundwater and absorb flood peaks. Seoul's Cheonggyecheon restoration replaced 5.8 km of elevated expressway with a stream corridor that was 3.3–5.9°C cooler than a parallel road nearby (UNEP).
• Cool and permeable surfaces paired with vegetation. Reflective roofs and permeable paving are not NbS by themselves. Paired with trees, they deal with the night-time heat that greenery alone can miss. CSE found that Delhi's green cover increase helped daytime temperatures but did not reduce night-time heat.
• Restored ridges and urban commons. Native landscapes such as the Delhi Ridge and the Aravallis act as cooling, groundwater-recharge and biodiversity refuges.

Three cross-cutting caveats apply. First, choose species carefully. Some trees, such as many eucalyptus, poplar and oak species, emit high levels of isoprene and other volatile organic compounds that can add to ozone formation in NOx-heavy cities (Sicard et al., 2018). Second, avoid heavy pollen producers near homes, schools and hospitals. Third, choose native species by default and remove invasives such as Prosopis juliflora (vilayati kikar).

What's working: real examples

Ahmedabad (India): South Asia's first Heat Action Plan (2013) is mainly an early-warning and health-response system, not an NbS. But it is the governance model every heat-plus-nature programme should copy. A peer-reviewed evaluation estimated about 1,190 avoided deaths a year in 2014–15. In 2017 the city added a cool-roofs pilot targeting 3,000 low-income homes.

Delhi NCR: About 7,784 hectares of the Delhi Ridge, the northern tip of the Aravallis, are notified for protection as forest, though final notification is still incomplete. In Gurugram, a former quarry was restored by citizens' group iamgurgaon, the municipal corporation, 68 corporates and more than 50 schools into the roughly 390-acre Aravali Biodiversity Park. In 2022 it became India's first OECM (other effective area-based conservation measure) site. FAO reports 85–95% plant survival. Across Delhi, the India State of Forest Report 2023 puts forest and tree cover at 25.03% of the city's area.

Hyderabad: CSE found the city more than doubled its green cover between 2003 and 2023, from 8.9% to 26.5%, the fastest rise among India's megacities.

Medellín (Colombia): Between 2016 and 2019 the city built more than 30 green corridors along roads and waterways. C40 reports an average cooling of about 2°C, with drops of up to 10°C in some places, along with lower PM2.5. It won the 2019 Ashden Award for Cooling by Nature.

Paris and Singapore: Paris's “Cours Oasis” programme has turned more than 200 asphalt schoolyards into shaded, permeable cool islands that open to the public during heatwaves. Singapore's OneMillionTrees movement aims to plant one million more trees by 2030, and NParks expects to reach the target around 2027.

The evidence also scales up. A Lancet study of 93 European cities estimated that raising tree cover to 30% could have prevented about 2,644 of the 6,700 summer deaths attributed to urban heat in 2015.

How to do it: a practitioner's checklist

• Map the hotspots. Overlay satellite land surface temperature with CPCB air-quality data and ward-level population. Include night-time heat.
• Prioritise by vulnerability. Start where heat, pollution and poverty overlap: informal settlements, markets, schools, hospitals and labour camps.
• Blend the finance. Municipal budgets can anchor programmes. CSR spending under Schedule VII item (iv) of the Companies Act explicitly covers environmental sustainability, agroforestry and “maintaining quality of soil, air and water”. Ghaziabad's ₹150 crore issue in 2021, India's first municipal green bond, shows the market exists, although it funded a sewage treatment plant rather than NbS. India's Green Credit Programme issues credits for restoring degraded forest land only after five years and at least 40% canopy density. That is the outcome-based design we need. Carbon and biodiversity credits and blended finance can add to these, but only with strong integrity safeguards.
• Involve communities. Resident welfare associations, schools and trained local gardeners keep projects alive, as Medellín and Gurugram both show.
• Budget for maintenance from day one. Medellín's corridors cost about US$625,000 a year to maintain in 2022 (BBC). Plan for at least three to five years of aftercare.
• Measure what matters. Track surface and air temperature, local PM2.5 and ozone, canopy cover, survival and biodiversity against a baseline, with independent verification.

Why this belongs in your ESG disclosures

For Indian listed companies, urban NbS links directly to environmental and community disclosures under SEBI's BRSR. Companies applying the TNFD framework can report their dependencies and impacts on nature in specific locations. For companies still in scope of the EU's CSRD after the 2026 Omnibus simplification, the biodiversity and pollution standards (ESRS E4 and E2) apply.

The opportunity is to move CSR plantation spending from counting saplings to reporting outcomes: degrees cooled, canopy that survives and air quality that improves.

The call to action

City officials: treat green and blue infrastructure as core infrastructure, with budget lines and maintenance contracts. Corporates and funders: commit to multi-year, outcome-linked NbS partnerships with cities instead of one-day planting drives. ESG professionals: push for heat and air-quality metrics in NbS disclosures.

Nature won't fix stubble burning or vehicle exhaust on its own. Cutting emissions at source comes first. But nature is the one intervention that cools, cleans, shades, recharges and protects biodiversity all at once. Let's fund it, maintain it and measure it like the infrastructure it is.