coverage
The world, and the datasets we use.
We select the reanalysis data by selecting the most granular database for the location. Hover over any area for details. We also access the CHELSA database, at a resolution of roughly 1 km × 1 km, for certain data types at all on-land locations.
explore
Spin the globe. Find your site.
Drag to turn it, or jump to a region. Point at any place to see which database a search there would use.
grid size
Database cell sizes, compared.
The granularity of a reanalysis database impacts how accurate the data may or may not be for your exact site. Reanalysis database cell sizes are usually based on degrees of latitude and longitude, which result in a 'rough' size depending on where you are in the world.
Here is roughly how the grid cells for different databases compare, although the exact size of the cell depends on where on the globe you are.
one cell per dataset · 30 px per km
grid explorer
Zoom in until the cells appear.
The grids each data set is built from, drawn cell by cell. At world scale every cell is smaller than a pixel: ERA5-Land's grid shows up first as you zoom in, then CERRA's, then NORA3's. Drag to move, scroll or pinch to zoom, untick a grid to hide it, and point at any place to see its cell in each dataset.
datasets
Our current datasets and their historical domains.
| dataset | grid | cell area | coverage | complete years | provider |
|---|---|---|---|---|---|
| ERA5-Land | 0.1°, ~9 km | 81 km² | Global, all land | 1950 – 2025 | ECMWF / Copernicus C3S |
| CERRA | ~0.05°, 5.5 km | 30.25 km² | Europe | 1984 – 2020 | ECMWF / Copernicus C3S |
| NORA3 | ~0.027°, 3 km | 9 km² | Northern Europe, land only, excl. Russia | 1996 – 2025 | MET Norway |
| CHELSA V2.1 | 0.0083°, ~0.93 km | 0.86 km² | Global, land | 1941 – 2025(last year may be partial) | WSL (Karger et al.) |
site elevation
How we handle the site's elevation.
A reanalysis database grid cell describes the climate at the average elevation of the whole cell area. In the mountains that can sit hundreds of metres above or below the site. We transform certain variables of the reanalysis data to account for the difference in height between the cell average elevation and the site elevation, to a 90-m plan accuracy.
Elevation shift example: section taken north–south through Innsbruck, Austria, in the Alps.
- Find the site's height. The Copernicus GLO-90 terrain model (90 m) is sampled at the exact coordinates of the search.
- Find the height the data refers to.
- Adjust every hour for the difference: air temperature, humidity (dew point and relative humidity), air pressure and sunlight. Skipped when the two heights are less than 1 m apart.
- Record and check it. The EPW file's header states the correction, for example "source referenced to 1,302 m; re-referenced to site elevation 580 m (Δz −722 m)". A check then compares the file's typical air pressure with the standard pressure at the header's elevation and warns if the two differ by more than 15 %, which would point to a wrong elevation.
future climate
From today's EPW file to a future one.
A future EPW file is the site-specific EPW file shifted to a target year – a process frequently referred to as morphing: same site, same hours, changed by what the CMIP6 climate models project for the associated emission scenario. C4B currently utilizes the global CMIP6 climate models for emission scenarios. For now, we only morph site-specific EPW files, not the climate.onebuilding.org weather station files.
- Site-specific EPW fileone typical year, compiled from a 15-year history, e.g. 2011 – 2025
- Monthly change factorsfor the associated scenario and target year. CMIP6 ensemble median
- Morphingevery hour, shifted to the future
- Future EPW fileone per scenario and target year
- One file per scenario and target year. Each future EPW file stands for one target year between 2025 and 2100 and one of the five shared socioeconomic pathways (SSPs):SSP1-1.9 very low emissionsSSP1-2.6 low emissionsSSP2-4.5 intermediateSSP3-7.0 high emissionsSSP5-8.5 very high emissions
We do not automatically produce a morphed file for SSP1-1.9, as we have already exceeded this emissions target, and the earth has warmed beyond this scenario. A user can choose to produce this scenario at their option.
- The file's own period comes first. The CMIP6 changes are measured using 1995 – 2014 as a baseline. A file compiled from 2011 – 2025 already contains the warming up to its centre, 2018, so only the change between 2018 and the target year is added; nothing is counted twice. An EPW file is created based on a year range, and the year at the center of this range defines the starting point for morphing.
- The monthly change factors come from the World Bank's CCKP climate portal. It publishes the CMIP6 ensemble median for four 20-year windows (2020 – 39, 2040 – 59, 2060 – 79, 2080 – 99). Target year values are interpolated between windows medians.
- Every hour is morphed for air temperature, sunlight, sky longwave radiation, humidity, cloud cover, and wind. Unless noted otherwise, we are currently not morphing precipitation, although a similar methodology is available.
See it for your site
Site-specific weather data
A typical-year weather file compiled from reanalysis at the project's coordinates, alongside the nearest station.
Future climate scenarios
Future weather files for any year up to 2100 under five SSP scenarios, overlaid on the project's analyses.
Precipitation and rainfall intensity
Monthly rain and snow, daily and hourly rain event intensity (15 minutes where recorded), and a long rainfall record in projects.
See your site's climate before design begins
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References
- Copernicus Climate Data Store: ERA5-Land hourly data
- Copernicus Climate Data Store: CERRA regional reanalysis for Europe
- NORA3 atmosphere hindcast data (Norwegian Meteorological Institute)
- Open-Meteo: Historical Weather API (data sources and models)
- World Bank Climate Change Knowledge Portal: data metadata
- Eames et al. (2024), A revised morphing algorithm for creating future weather for building performance evaluation
- NOAA NCEI: Global Historical Climatology Network daily (GHCNd)
- NOAA NCEI: Global Historical Climatology Network hourly (GHCNh)
- Climate.OneBuilding.Org: TMYx typical meteorological years
Related guides
EPW weather files
What is inside an EPW weather file, where the data comes from, and how to open, check and use one on a project.
Typical meteorological year (TMY)
How typical meteorological years are selected, how TMY, TMYx and ISO 15927-4 reference years differ, and when to use actual or extreme years instead.
Reanalysis data and ERA5
How reanalysis datasets such as ERA5, ERA5-Land, CERRA and NORA3 work, what their resolution means for a building site, and how they compare with station data.
Future weather files and morphing
How morphing combines an observed weather year with climate model projections, how the methods differ and what future weather files can and cannot tell you.
SSP climate scenarios
What the five main SSP scenarios mean, how much warming each implies over a building's life and how to choose scenarios for design.