The Global Centre for Risk and Innovation (GCRI)
Cities are hotter than their surroundings, and their buildings decide how much of that heat reaches the people inside. Dark surfaces, dense construction, little shade and waste heat raise urban temperatures, while poorly insulated or unventilated homes trap heat at night. This page sets out how urban heat develops, how it is measured inside and out, and what evidence serves the health, housing and city authorities that respond to it.
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For buildings and heat, in GCRI's spatial-intelligence reading, the map opens on daytime surface heat, true-colour imagery and population density with relief in 3D, a past-year temperature and sunshine chart at the centre and true colour from NASA GIBS, framed on India; 3 further NASA layers wait in the list.Satellite and model products as NASA publishes them, each with its own date; indicators, not assessments of any place; claim ceiling INTEGRATED.
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Urban heat is the extra heat that cities generate and trap, through dark surfaces, dense construction, little vegetation and waste heat. Buildings decide how much reaches people indoors, and exposure falls hardest on older, ill and poorly housed residents. Satellites, stations and indoor sensors measure different parts of it.
The working screen behind this subject: its structure, terms and states. Names are placeholders and values illustrative.
Building performance and urban heat. The dossier below sets out how the risk develops, what is measured, where the data come from, how it is modelled and who decides.
Paved and built surfaces absorb sunlight and release it slowly, while less vegetation means less evaporative cooling. Cities stay warmer than rural areas, especially at night.
Insulation, orientation, glazing, ventilation, thermal mass and roof colour set indoor temperatures. Top-floor flats and lightweight roofs can be much hotter than outside air.
Older people, those with chronic illness, outdoor workers and people in poor housing face the greatest risk. Hot neighbourhoods often have fewer trees and poorer housing.
Air conditioning protects health but raises electricity demand and waste heat. Peak demand during heatwaves can strain grids, and those who cannot afford cooling remain exposed.
Each term as this page uses it. Where a standard-setting body defines the term, the wording follows that body.
| Term | Definition |
|---|---|
| Land surface temperature | The temperature of the ground and building surfaces as measured by satellite thermal sensors. |
| Indoor overheating | Indoor temperatures high enough to cause discomfort or health risk, judged against stated criteria. |
| Heat-health action plan | A plan that sets warnings, actions and responsibilities to protect health during hot weather. |
Each indicator carries its unit, its cadence, the kind of source behind it and the evidence label a value would carry. No values are shown: a programme supplies them under its own authority.
| Indicator | Unit | Cadence | Source type | Label |
|---|---|---|---|---|
| Land surface temperature | degrees Celsius | per satellite overpass | Satellite thermal imagery | OBSERVED |
| Air temperature difference urban to rural | degrees Celsius | hourly | Urban and reference weather stations | OBSERVED |
| Indoor temperature in monitored dwellings | degrees Celsius | hourly | Indoor sensors | OBSERVED |
| Tree canopy cover | percent of area | per assessment | Aerial and satellite imagery | OBSERVED |
| Heat-related excess mortality | deaths above expected | per heat season | Mortality statistics and models | ESTIMATED |
| Households with access to cooling | percent of households | per survey | Household surveys | REPORTED |
The topic as a computational graph: named sources feed the methods, an evidence review gates the outputs, and the decisions stay with the authorities that hold them.
Fig. 02Nodes carry their type, two metric rows and a state; connectors show what feeds what; dashed frames name the owners; the timeline is the cadence. Design of the pipeline, not a record of a run.
Named public datasets and institutional records, each with its licence class. Sources by agreement are used only under their terms and never republished.
| Source | What it gives | Licence class |
|---|---|---|
| Landsat Collection 2 surface temperature (USGS) | Land surface temperature at thirty-metre resolution | Public domain, US government data |
| ECOSTRESS (NASA) | Land surface temperature at different times of day | Open, NASA data policy |
| Copernicus Urban Atlas and street tree layer | Urban land use and trees for European cities | Free, Copernicus terms |
| WHO and WMO heat-health guidance | Heat-health action planning and warning systems | Public, WHO and WMO terms of use |
| IEA cooling and buildings data | Cooling demand and appliance ownership | Licence per dataset (to check) |
Cities and Built Environment prepares evidence. The decisions below are taken by the authorities named, under their own rules, and never by the platform.
| Who decides | The question | Evidence this page serves |
|---|---|---|
| City governments | Where to plant trees, add shade and cool surfaces first | Heat maps; canopy cover; vulnerability profiles |
| Public health agencies | Who to reach and when during heatwaves | Vulnerability profiles; excess mortality evidence |
| Building regulators and housing agencies | Which standards and retrofits prevent indoor overheating | Indoor overheating assessments |
Which neighbourhoods and building types reach the highest indoor and outdoor temperatures.
Older people, people living alone, those with chronic illness, outdoor workers and residents of top-floor or poorly ventilated homes.
The effect of shading, insulation, ventilation, reflective surfaces and thermal mass.
How rising air-conditioning demand interacts with power supply during heatwaves.
The urban heat island arises because built surfaces absorb and store solar energy and release it slowly, vegetation and evaporation are reduced, and vehicles, industry and cooling equipment add waste heat. Night-time warmth is particularly harmful because bodies cannot recover.
Indoor conditions depend on design. Lightweight roofs, large unshaded glazing and poor ventilation can make homes hotter than outdoors. Insulation helps or harms depending on climate and ventilation. Mechanical cooling protects occupants but raises electricity demand and adds heat outside.
Heat risk is social. Isolation, poverty and illness turn high temperatures into deaths, which is why public health and housing must be considered together.
| Method or data | What it shows | Its limit |
|---|---|---|
| Thermal satellite imagery | Surface temperature patterns | Surface is not air or indoor temperature |
| Street and indoor sensors | Actual temperatures people experience | Sparse networks, calibration needs |
| Building energy simulation | Performance of design options | Depends on occupant behaviour assumptions |
| Health records | Heat-related illness and mortality | Under-recording and attribution limits |
The current service level is R0: information and enquiries. An enquiry receives a reference and names the next step; applications, payments, compute allocations and registrations open only when their team, terms and review capacity exist.