Urban Climate Index
Methodology
The Urban Climate Index is a published score for one city, one area of interest and one month. We publish cities around the world, through the year.
Published score form
Urban Climate Index = z(LST) + 0.4 × z(air) + 0.3 × z(humidity) − 0.15 × z(rain)
* Generic published form for a hot-month reading. Each z is standardized across the zones of that same cut; lower is more comfortable.
** The index adapts its rules to the particular conditions of each city. A cold month flips comfort direction. Land surface temperature keeps weight 1. Wind weight is stated on each cut.
Land surface temperature
We use satellite land surface temperature for the monthly composite.
The month is a median composite of the usable satellite scenes. We discard scenes whose cloud mask covers most of the urban footprint for that overpass. Only clear thermal pixels enter the composite. It is not thirty daily readings.
We keep urban ground: residential, commercial, industrial, retail, and parks. Wetlands, lagoons and forest stay out of the score.
Official stations
Air, humidity and rain come from that country’s official station network: the national meteorological service.
Each zone takes those readings from the nearest official station that reports each one. There is no interpolated humidity or rain surface. Those station readings enter the score as z-scores alongside land surface temperature.
The same stations may also record wind. Whether wind has weight in a given cut is stated in that cut’s published rule.
Season rules
In a cold-month cut, comfort runs the other way: a higher score is more comfortable. That cut’s published rule states the direction.
The index adapts its rules to the particular conditions of each city.
Land surface temperature dominates because its weight is 1. Humidity and rain only move a zone when that zone uses a different station from its neighbours.
Metro and city core
When the city has a metropolitan area, we publish both readings: the metro area and the city core. Greater Sydney and Sydney City Council. They are two rankings. They are not mixed.
Read more on the blog
City notes that use this method:
#Lima-and-Callao#Peru#Lima-district#Aguascalientes#Mexico
Lima and Callao, PeruSeptember-2026
Urban Climate Index for the Lima and Callao metropolitan area in September 2026: heat across 49 municipalities
The Urban Climate Index for September 2026 in the Lima and Callao metropolitan area, on the Pacific: 49 municipalities. Villa El Salvador leads the list, at 24.2°C, and Pucusana closes it.
Lima district, PeruSeptember-2026
Urban Climate Index for the Lima district in September 2026: heat across 20 sectors
The Urban Climate Index for September 2026 in the Lima district, on the Pacific: 20 sectors. Sector 17 leads the list, at 37.2°C, and Sector 9 closes it.
Aguascalientes, MexicoAugust-2026
Urban Climate Index for the Aguascalientes metropolitan area, Mexico, in August 2026: the heat across 3 municipalities
The Urban Climate Index for August 2026 in the Aguascalientes metropolitan area, in the Bajío: 3 municipalities. Jesús María leads this list, at a temperature of 38.2°C, and Aguascalientes closes it.
Method questions
What is the difference between surface temperature and air temperature?
Surface is land surface temperature on the ground from the thermal month. Air is what the official station measures. They are two different readings. The index uses both. It does not treat them as one heat island class.
Where does the surface temperature come from?
From satellite data: a monthly thermal composite of usable scenes after cloud screening. It is not thirty daily readings.
Which weather stations?
The official station network of that country — the national meteorological service. Each zone takes the nearest station that has that variable. There is no interpolated humidity or rain surface.
Does wind enter the score?
Stations may record wind. Whether wind has weight is stated on each cut’s published rule. The form above uses land surface temperature, air, humidity and rain unless that cut says otherwise.
Why can a green edge win a city?
Parks are urban ground, so a neighbourhood with parks can lead the heat ranking. The index ranks heat. It does not crown a place to live.
What about winter or a tropical city?
The hot-month form is for heat comfort: lower is more comfortable. A cold month flips that direction under its own published rule. The published rule adapts to that city’s conditions; cities are not forced into the weights above.