Cooling options by place, and what keeps them working
What to build or change where people are: homes, outdoor work, schools, markets, waiting areas, heat with waterlogging and greening where water is short. With what keeps each option working, rough costs and the traps to avoid.
Open the interactive cooling optionsHomes
Protects: Sleep, care work, and the older people, young children and sick people who spend the hottest hours indoors.
Key caution: Check the roof type, fire safety, tenure and ventilation before any retrofit.
- Reflective roof coating. A white, solar-reflective coat on the roof, so less of the sun’s heat passes into the room below. Keeps working with: Repainting every few years, and a thermometer to check it works. Avoid: Promising a fixed number of degrees before you have measured.
- Lime whitewash. A cheap seasonal white coat that households can apply themselves when a commercial coating is out of reach. Keeps working with: Recoating every season, by a named group. Avoid: Treating it as a lasting retrofit.
- Better roof panels. Replace or cover thin tin or asbestos sheets with an insulated roof panel. Keeps working with: A structural check, and secure enough tenure to make the investment safe. Avoid: Scaling up before checking structure and tenure.
- Insulation under the roof. A fire-safe layer or false ceiling that slows heat coming through the roof. Keeps working with: A fire-safety review of the material. Avoid: Flammable sheets near kitchens or wiring.
- Shade on walls and windows. Bamboo blinds, jute screens or awnings on the sunny side stop sunlight before it reaches the room. Keeps working with: Fixing and replacing screens each season. Avoid: Blocking airflow or all daylight.
- Let the air through. Higher vents and openings that let hot air out at night. Keeps working with: Security, rain protection and mosquito screens. Avoid: Openings that let in dust, rain or intruders.
In 16 homes in an Ahmedabad informal settlement, measured in September 2017, rooms under a modular roof averaged about 33.8 °C against 36.8 °C under asbestos sheets. White paint on tin did not beat asbestos or concrete in the same comparison: measure before you promise. Vellingiri et al., Indian Journal of Occupational and Environmental Medicine, 2020
In a two-year trial in Burkina Faso, cool roofs lowered indoor temperatures by 1.2 °C in tin-and-mud homes and 1.7 °C in tin-roofed homes, and residents’ heart rates fell. The same team began a year-long trial in about 400 Ahmedabad homes in 2025. Reuters, via South China Morning Post, 2025
Kitchen heat
Cooking adds heat on top of the weather, often in the smallest, least ventilated room, and usually for women. In Nepal’s Madhesh Province, women cooking in hot, smoky kitchens carry a daily ‘thermal labour’ that falls hardest on women in the poorest single-room homes with little access to clean energy or credit. Ghimire and others, Frontiers in Public Health, 2025
- How much heat does the stove give off, and does anyone sit beside it for long?
- Can hot air and smoke get out: a window, a vent, a gap under the roof?
- Is there smoke from wood, dung or kerosene adding to the strain?
- How long is cooking each day, and can some of it move to cooler hours?
- Can the household afford cleaner fuel through the season, not only once?
- Is the electricity reliable enough for a fan or an electric cooker when it is hottest?
Outdoor work
Protects: People whose income depends on being outdoors in the hottest hours: vendors, loaders, builders, sanitation workers, traffic police.
Key caution: A shelter without water, paid rest or a change of hours is not worker protection.
- Rest shelters on work routes. Shade, seating and water where workers can recover during a shift. Keeps working with: Paid rest time, and someone who cleans and refills it. Avoid: Treating the shelter as a substitute for work rules.
- Drinking water and rehydration salts. Refill points with safe water and oral rehydration salts at markets, sites and junctions. Keeps working with: A daily refill and cleaning roster, often ₹500–2,000 a day. Avoid: Counting it as cooling: it protects bodies, not temperatures.
- Shade nets. Quick shade over junctions, queues and work yards. Keeps working with: Poles set firmly into the ground, and nets up before the heat starts. Avoid: Bamboo frames that fall in the first storm.
- Shade trees on work routes. Canopy along the streets where people work and wait. Keeps working with: Water, root space and three years of care. Avoid: Counting saplings planted instead of canopy that survives.
- Misting at hotspots. Fine water spray at a few crowded, dry spots. Keeps working with: Safe water, drainage, filters and a technician. Avoid: Humid places and water-short cities: in humid heat the benefit roughly halves.
Nagpur strung green shade nets over 10–12 busy junctions in May 2026. Several tore or collapsed in strong winds, and residents pointed out the heat had begun at the end of March. A net had also fallen at Tukdoji Square in 2025 because its bamboo was not set firmly into the road. The Hitavada, 11 May 2026
Comparing Phoenix with humid Houston, misters still cut heat stress in the humid city, but with about half the benefit, and only when there was some wind. US National Science Foundation public access repository
Schools and childcare
Protects: Learning, play, attendance and drinking water for children and the staff who look after them.
Key caution: Count shade and surviving trees, not saplings planted.
- Cool classroom roofs. A reflective coat or a ventilated second roof over the hottest classrooms. Keeps working with: A line in the school’s maintenance budget. Avoid: Roof canopies that are not anchored for monsoon winds.
- Shaded play space. Trees, shade structures and less hard paving where children play. Keeps working with: Watering through the holidays, when nobody is at school. Avoid: Planting that dies in the first summer break.
- Shade on classroom windows. Screens or awnings on the sunny side of classrooms. Keeps working with: Fixing them back after each monsoon. Avoid: Making rooms so dark that lights and fans run all day.
- Drinking water at school. Enough safe, cool water for every child, with time in the timetable to drink it. Keeps working with: Filter changes and cleaning. Avoid: One tap for hundreds of children.
Researchers who studied how age groups use green spaces found that older people asked for benches, shelter during extreme weather and safe paths, while children wanted trees for shade and places to play. Ask both before you design. Frantzeskaki et al., chapter 11 in Nature-Based Solutions for Cities, 2023
Markets and street vending
Protects: Vendors’ income and stock, customers, and the porters who load and unload in the heat.
Key caution: Design it with the vendors and protect their place, or the upgrade becomes an eviction.
- Shade over stalls and aisles. Nets, fabric or a light frame with climbing plants over the places vendors sit. Keeps working with: Storm-proof fixing and someone to replace worn cloth. Avoid: Shade that blocks fire access or loading.
- Water and rehydration points. Safe drinking water for vendors and customers. Keeps working with: A refill and cleaning roster agreed with the market association. Avoid: Points nobody is responsible for.
- Planted drains and rain gardens. Planted channels and hollows that soak up runoff so the market does not flood after a storm. Keeps working with: Rubbish collection, or they clog. Avoid: Building them where waste is dumped.
- A whole-market package. Shade, water, cool roofs, drainage, trees and waste collection together, run with the vendors. Keeps working with: A vendor committee with a say over the design and the upkeep. Avoid: Beautification that pushes informal vendors out.
India’s Street Vendors Act (2014) gives vendors 40% of the seats on each town vending committee and says no vendor may be evicted or relocated until a survey of existing vendors is complete: a hook for designing market cooling with vendors, not around them. Street Vendors (Protection of Livelihood and Regulation of Street Vending) Act, 2014, on FAOLEX
Bus stops and queues
Protects: Commuters, patients queuing at clinics, people waiting for rations or wages, and visitors.
Key caution: Put the shade where people actually stand, at the hours they wait.
- Cool waiting points. Shade, a bench, drinking water and a board showing the heat alert, at bus stops, clinics and ration shops. Keeps working with: Access for older and disabled people, and someone who refills the water. Avoid: Counting shelters built instead of people protected.
- Planted bus stops. Climbers on a frame that shade the stop more each year. Keeps working with: Watering and pruning. Avoid: Living shade with no water plan.
- Trees where queues form. Canopy over the places people wait every day. Keeps working with: Root space, water and three years of care. Avoid: Planting where the queue isn’t.
- Shorter waits. Appointment slots, token systems and timed services so fewer people stand in the sun at midday. Keeps working with: Agreement from the clinic, office or transport operator. Avoid: Assuming shade is the only answer.
Measuring how hot people actually feel on summer days in Tempe, Arizona, researchers found shade from buildings cooled most by day, then trees, then light structures such as sails. Air temperature barely differed between them, and every kind of shade held heat after sunset. Middel et al., 50 Grades of Shade, Bulletin of the American Meteorological Society
Heat and waterlogging
Protects: Neighbourhoods that bake in summer and flood in the monsoon, and the groundwater both depend on.
Key caution: Stop sewage and rubbish flowing in, and fund the desilting, before calling it blue-green.
- Sponge parks. Small parks shaped to hold, soak up and slowly release stormwater, with plants that cool the area around them. Keeps working with: An overflow, mosquito control and desilting before each monsoon. Avoid: Standing water.
- Restored ponds and lakes. Desilted, protected water bodies with planted edges that store floodwater, recharge groundwater and cool their surroundings. Keeps working with: Sewage diverted away, and rubbish kept out. Avoid: Calling a polluted pond a cooling asset.
- Planted drains and rain gardens. Channels and hollows that slow, clean and soak up runoff from roofs and lanes. Keeps working with: Rubbish collection and an overflow. Avoid: Places where they will become open garbage drains.
- Permeable paving. Paving that lets rain soak in instead of running off. Keeps working with: Regular cleaning so it does not clog. Avoid: Claiming it cools unless there is shade and moist soil too.
- Recharge pits. Small pits that send roof and courtyard runoff into the ground. Keeps working with: A filter, so polluted water does not reach shallow wells. Avoid: Recharging dirty runoff.
Over four years, Greater Chennai Corporation restored 70 ponds for ₹144.34 crore and built 88 rainwater-harvesting parks for ₹14.74 crore. The News Minute
Bangkok’s Benjakitti Forest Park, a former tobacco factory turned wetland, is designed to hold 87 million litres of water. Mongabay, 2024
China’s sponge-city pilots in 30 cities (2014–2019) often built projects one at a time instead of as a city-wide system, struggled to get engineers and designers working together, and left cities worried about paying for more once pilot money ended. McPhillips et al., chapter 7 in Nature-Based Solutions for Cities, 2023
Jakarta’s green space was about 5.2–5.6% of the city in 2024–25, sources differ, against a legal target of 30%, now pushed back to 2045. Metro TV News
Greening where water is short
Protects: Trees, soil moisture and groundwater, and the long-term shade they give.
Key caution: Planting without water, soil care and a survival budget is not adaptation.
- Care for the trees you have. Better tree pits, mulch, compost and looser soil so existing trees take up water and survive. Keeps working with: A yearly care round. Avoid: Replanting instead of fixing why trees die.
- Rainwater for trees. Store runoff from roofs and streets to water trees and gardens through dry spells. Keeps working with: Clean tanks and a plan for the dry months. Avoid: Planting with no water source at all.
- Treated wastewater for parks. Use treated water from a treatment plant for parks and tree corridors, so greenery does not compete with drinking water. Keeps working with: Treatment that is checked. Avoid: Untreated sewage on public land.
- Street trees with three years’ care. Hardy, shade-giving species, chosen for the heat and drought ahead. Keeps working with: Species choice, root space, water and a named owner. Avoid: Counting planted trees.
- Dense mini-forests. Small, densely planted native woods on spare public land. Keeps working with: Water through the first years. Avoid: Assuming they beat ordinary shade trees on value.
In Berlin’s Johannisthal park, more than 500 of 870 newly planted native trees died within ten years despite watering, so the shade and cooling never arrived. Across the city, about 44,000 street trees were cut between 2012 and 2019 and about 18,000 planted. Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023
In Santiago de Chile, how well a municipality manages its trees was the strongest predictor of whether they survive, and wealthier municipalities spend far more on it. Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023
Making it last
Protects: Every asset above: who targets it, who opens it on an alert, who pays for upkeep, and who hears complaints.
Key caution: Often the most useful layer, and the easiest to leave unfunded.
- Link the heat plan to the assets. A ward or settlement plan that says which shelters, water points and cool spaces open at each alert level, and who opens them. Keeps working with: A yearly review with the people who use them. Avoid: A plan with no budget or named owners.
- An upkeep agreement. A written deal between the council, community groups, schools or vendors on who repaints, waters, prunes, refills and repairs. Keeps working with: Money from the running budget, not only the building budget. Avoid: Paying to build without paying to maintain.
- Map risk with the people exposed. Walk the area with workers, women, older and disabled people, migrants and renters to see who is exposed, why warnings fail, and where assets could go. Keeps working with: Repeating it as people and places change. Avoid: Relying on satellite heat maps alone.
- A way to complain and be heard. An accessible route for complaints and feedback, set up before work starts. Keeps working with: Someone who answers within a set time. Avoid: Starting work where affected people have no voice or remedy.
- Find the hooks in existing plans. Search city, disaster, water and climate plans and budgets for mandates and money that cooling can use. Keeps working with: Checking what you find with the officials concerned. Avoid: Assuming nothing exists because nobody uses the words “nature-based solutions”.
In Melbourne, officials found money for new green infrastructure was usually available, but running budgets were under pressure and rarely increased, even as the area to maintain grew. Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023
In Santiago, without long-term financing, only better-off municipalities could take part in green-space programmes, because only they could afford the extra upkeep. Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023
Less than 10% of the climate finance that reaches cities goes to adaptation and resilience. Cities Climate Finance Leadership Alliance, The State of Cities Climate Finance, 2021
The IUCN Global Standard for Nature-based Solutions makes inclusive governance and equity one of its eight criteria. IUCN Global Standard: the eight criteria
Questions before you choose
Avoid: Cut the need for cooling first: shade, cooler roofs, air flow and trees. Improve: Where machines are needed, choose efficient ones that run on the power and water you really have. Expand access: Make sure the people most exposed can reach cooling and afford to keep it running. Clean Cooling Collaborative’s three goals, summarised by Philanthropy Asia Alliance
- Does it need electricity, and is the supply reliable in the hottest weeks?
- What happens in a power cut: does it stop, or keep cooling without power?
- Does it need water, and where will that water come from in a dry spell?
- Who services or repairs it, and how fast?
- Who owns the running cost each year, and from which budget?
- Who can use it: renters, women, older people, people with disabilities?
Keep the outcomes apart. Name the outcome you want: a cooler room, people feeling comfortable, less heat strain on the body, fewer illnesses, or income kept. They are different. A cooler room does not prove better health, and comfort does not prove less strain, so measure the one you mean.
Five traps that waste cooling money
- Buying before diagnosing. The asset is chosen before anyone has mapped who is exposed, where and why, so the shade ends up where nobody waits. Instead: Start with the people and places at risk, then choose.
- Built, with no one to keep it. It looks good for one season, then fades because no running budget or owner was set aside. Instead: Name who keeps each asset working after year one, and from which budget.
- Green without water. Trees, parks and green roofs go in with no water source, soil care or survival budget. Instead: Secure the water and three years of care before planting, and count trees that survive.
- Promising degrees you haven’t measured. A fixed temperature drop is promised from another place’s study. Instead: Log temperatures in treated and untreated places, and report what you measured.
- A list of activities, not a model. A proposal lists many activities, but none says who it protects, what it costs per unit, who owns it and what changes. Instead: For each option, name the users, the unit cost, the owner and the outcome.
What changes the result
Shade beats air temperature
In hot, sunny places, how hot people feel outdoors depends more on radiant heat from the sun and surfaces than on air temperature. Shade from buildings cooled most by day in a Tempe study, then trees, then light structures. Middel et al., 50 Grades of Shade
Reflective paving can make walking hotter
In Los Angeles, coated roads were up to 6 °C cooler on the surface, but pedestrians above them received about 4 °C more radiant heat. Pair reflective surfaces with shade. Arizona State University, 2020
Misting depends on humidity and air movement
In Singapore, a misting fan cut air temperature by about 1.5 °C and made people feel cooler. An overhead misting line without fans made no significant difference. Review in Clean Technologies, MDPI, 2021
Trees cool people more than thermometers show
WRI’s Cool Cities Lab puts the improvement trees make to thermal comfort at roughly 2–8 °C. That measures how hot people feel, which is not the same as air temperature. World Resources Institute: Urban trees, an underused tool for keeping people cool
Four heats in a home
A heat warning gives one number: the air temperature in the shade. A family under a tin roof lives with four heats at once, and the worst of it often comes after dark.
- Outdoor air. The temperature a weather station measures, in the shade. It is the number in almost every heat warning, but not what people feel inside a tin-roofed room.
- The roof. Sun-baked sheet metal gets far hotter than the air. Roofs of informal homes in Mumbai and Pune measured above 50 °C when the air was about 30 °C. Urban Solutions: how informal settlements stay cool (informal measurements)
- Radiant heat. A hot ceiling gives off heat onto the people below, like standing near a stove, so a room can feel hotter than its air. This is what mean radiant temperature measures.
- Indoor air. The air inside, held in by thin walls, few windows and crowded rooms.
At night. After sunset the street starts to cool, but thin-roofed homes cool slowly. In low-income homes measured in Dhaka, Delhi, Faisalabad and rural Maharashtra, temperatures in tin-roofed houses swung 3–4 °C more over the month than the outdoor air, and stayed warmer indoors because they cooled so slowly at night. Tasgaonkar et al., Scientific Data, 2022: indoor heat in low-income homes in South Asia
- 7.6 °C hotter, at most, for people in Ahmedabad’s informal settlements than for people in formal housing, in a survey of 860 households. Frontiers in Built Environment, 2022
- Up to 9 °C hotter indoors than outside, in pilot measurements in informal settlements in Kenya, Tanzania and Zimbabwe. IIED, 2026
- 2–5 °C cooler indoors under reflective roof paint than under ordinary roofs, in Ahmedabad’s informal settlements. NRDC: community-led cool roofs in four Indian cities
Indoors is not always hotter at midday: in an experiment in The Gambia, metal-roofed houses were about 1.4 °C cooler than the outdoor shade by day, but warmer at night. The danger is nights that do not cool. Malaria Journal, 2021: roof colour and indoor temperature in rural Gambia
For heat plans: Heat warnings measure the street. Heat plans can protect the room too: count indoor and night-time heat, warn for hot nights, and pay for cooler roofs where people sleep. Watch the film (1:25)
What cooling costs elsewhere in the region
In the 2021 International Comparison Program, India had the lowest price level among 21 Asia-Pacific economies for investment goods, which include construction. The same work usually costs more in Southeast Asia. Asian Development Bank, ICP 2021 results for India
- Ahmedabad, India: Solar-reflective roof paint, and a modular cool roof for a one-room home. About ₹25 per sq ft (≈US$2.80 per m²) for paint; about ₹27,000 (≈US$280) for a 9 m² modular roof lasting 25 years. Reflective paint kept homes 2–5 °C cooler indoors than ordinary roofs. Mahila Housing Trust, 2021 · NRDC: community-led cool roofs in four Indian cities
- Tangerang, Indonesia: Cool roof coating. A 40 kg set sold for Rp 2.73 million covers 120–160 m²: roughly Rp 17,000–23,000 per m² (≈US$1–1.50) by our arithmetic. Given free to schools and places of worship.. The Thaiger: Indonesia adopts cool roofs
- Philippines: Installed cool roofs. About ₱500–1,200 per m² (≈US$9–21), an industry estimate that its authors call a barrier for households earning about ₱25,000 a month. Ken Research: Philippines cool roof market
- Singapore: Cool paint on public housing blocks. Being rolled out to every HDB estate by 2030, at an extra cost of about S$60 million. Trials aimed to lower the air temperature around blocks by up to 2 °C. HDB: cool paint pilot in Tampines, 2021 · Northumbria University: cool coatings for all HDB estates by 2030
A World Bank cost-benefit study of Lucknow, Chennai and Surat found that heat-health early warning systems return more than 50 times their cost, and urban greening about three times, counting health and work alone. Jones et al., World Bank Policy Research Working Paper 10960, 2024
Putting a value on cooling
Modelled against housing built in its place, Guangzhou’s Haizhu wetland keeps the area within 600 m about 0.25 °C cooler on a typical summer day, and over 1 °C cooler on the site itself. Without it, productivity in nearby heavy outdoor work would fall by 2.5% in May and 16.1% in October, monthly risk of death would rise by 1.23–1.27% from June to September, and cooling bills would rise by about US$1.9 million over 30 years.
Most of the wetland’s US$146.8 million value comes from carbon and mental health, not cooling. So make the heat case in lives, heavy outdoor work and bills, not money alone. And the same cooling is worth most to people without air conditioning.
Sources: Guerry et al., chapter 12 in Nature-Based Solutions for Cities, 2023 · World Bank and GPSC: the Haizhu wetland assessment, 2022
Free books and guides
- Nature-Based Solutions for Cities The source for much of this section: cooling and air quality, planning and upkeep in Jakarta, Berlin, Melbourne and Santiago, governance, and how to value nature’s benefits.
- Nature-Based Solutions to Climate Change Adaptation in Urban Areas Evidence on cooling cities with green and blue infrastructure, then chapters on putting it into practice, social and environmental justice, governance and economics. Licensed CC BY 4.0.
- Heat Action Planning Guide for Neighborhoods of Greater Phoenix A step-by-step method for planning heat action with residents of three neighbourhoods: engage, co-design in workshops, then put it in place.
- Urbanization, Biodiversity and Ecosystem Services: Challenges and Opportunities The first global assessment of how cities affect nature. It found urban land growing faster than urban populations, with half of the world’s expected new urban land in Asia.
- Urban Planet: Knowledge towards Sustainable Cities Ways of knowing cities from sociology and political science to ecology and engineering, with contributions from architects, journalists, artists and activists.
- Resilient Urban Futures How nine cities in Latin America and the United States used participatory visioning with residents to imagine resilient futures.
- The State of Cities Climate Finance Maps the money: less than 10% of climate finance reaching cities goes to adaptation and resilience, and too little climate investment reaches cities in developing countries, singling out fast-urbanising South and Southeast Asia and Sub-Saharan Africa.