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UV Index Official Sources and Resources

UVI.today·

Understanding the UV index — where the data comes from, how forecasts are generated, and which organizations set the standards — helps you make informed decisions about sun exposure. This page collects the key official sources, data services, and scientific tools that underpin UV index monitoring worldwide, including those used by UVI.today to deliver hourly UV forecasts.

World Health Organization (WHO)

The WHO, together with the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP), and the International Commission on Non-Ionizing Radiation Protection (ICNIRP), created the standardized UV Index in 1994. The UV Index is a dimensionless linear scale starting at 0 (no UV radiation), with values grouped into five exposure categories: Low (0–2), Moderate (3–5), High (6–7), Very High (8–10), and Extreme (11+). UVI.today uses these WHO-defined categories and their associated colour codes to display current UV levels.

  • Global Solar UV Index: A Practical Guide (2002) — the joint WHO/WMO/UNEP/ICNIRP publication that defines the UV Index scale, exposure categories, and sun protection recommendations. This is the primary reference used by UVI.today for protection advice.
  • Ultraviolet radiation fact sheet — overview of UV radiation types (UVA, UVB, UVC), health effects including skin cancer and eye damage, and environmental risk factors such as ozone depletion, altitude, and surface reflection.
  • Sun protection Q&A — Q&A on UV radiation health effects and sun protection measures.

World Meteorological Organization (WMO)

The WMO coordinates global weather and atmospheric monitoring across 193 member states. Its Global Atmosphere Watch (GAW) programme includes a UV radiation monitoring network with ground-based stations that measure actual UV irradiance, providing validation data for satellite-based forecasts.

  • WMO Global Atmosphere Watch — the WMO programme responsible for atmospheric composition monitoring, including UV radiation measurement standards and station data.

Copernicus Atmosphere Monitoring Service (CAMS)

CAMS is operated by the European Centre for Medium-Range Weather Forecasts (ECMWF) as part of the EU's Copernicus programme. It produces global UV radiation forecasts up to five days ahead by combining numerical weather prediction models with satellite observations of ozone concentration, aerosol optical depth, and cloud cover. CAMS data, delivered via the ECMWF model chain, is the upstream source for the UV index values displayed on UVI.today.

  • CAMS global atmospheric composition forecasts — global forecast dataset including UV biologically effective dose and downward UV radiation at the surface, based on total column ozone from Copernicus Sentinel satellites, aerosol optical depth, and NWP cloud forecasts.
  • CAMS solar radiation — access to atmospheric composition data including ozone profiles, aerosol forecasts, and solar radiation products that affect UV levels at the surface.

Open-Meteo

Open-Meteo is an open-source weather API that aggregates data from national weather services and CAMS/ECMWF. It provides hourly UV index values as a standard variable alongside temperature, humidity, and other weather parameters. UVI.today retrieves its UV index forecast data from the Open-Meteo API in real time. Open-Meteo sources its UV data from the CAMS radiation forecast described above.

  • Open-Meteo Weather API — free, open-source weather API with UV index, temperature, precipitation, and more. Available for commercial use.

U.S. Environmental Protection Agency (EPA)

The EPA provides daily UV index forecasts for locations across the United States, calculated using ozone data and solar angle models. The EPA also maintains sun safety educational resources and the SunWise programme for schools and communities.

  • EPA UV Index — daily UV index forecast searchable by ZIP code and city, based on NWS/NOAA ozone forecast data.
  • SunWise programme — sun safety education resources, UV exposure guidelines, and outreach materials.

Australian Radiation Protection and Nuclear Safety Agency (ARPANSA)

Australia experiences some of the highest UV levels globally due to its latitude and thin ozone layer over the southern hemisphere. ARPANSA monitors UV radiation across the country.

  • ARPANSA — the Australian government agency responsible for radiation protection, including UV radiation monitoring.

International Commission on Non-Ionizing Radiation Protection (ICNIRP)

ICNIRP is an independent scientific body that co-developed the UV Index standard together with WHO. It publishes guidelines on occupational and public exposure limits for UV radiation, based on peer-reviewed research on the biological effects of UV on skin and eyes.

  • ICNIRP — UV (100–400 nm) — scientific publications and guidelines on ultraviolet radiation exposure.
  • ICNIRP — UV Index — information on the UV Index application, including how it is calculated and used for public health guidance.

GeoNames

GeoNames is an open geographical database containing over 11 million place names with coordinates, population data, and administrative divisions. UVI.today uses GeoNames data to identify cities, resolve location searches, and generate localized city names for UV index pages across all supported languages.

  • GeoNames — open geographical database (CC BY 4.0) with coordinates, alternate names, and administrative data for cities worldwide.