First global map of light pollution in Catalonia developed using advanced modelling

The Department of Territory, Housing and Ecological Transition has published the first global map of light pollution in Catalonia, developed using an advanced mathematical model that simulates the propagation of artificial light based on the physical characteristics of artificial night-time lighting and the composition of the atmosphere. The work, part of the 2024 night sky quality assessment campaign, has been carried out by the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) using resources and data provided by the secretariat of Ecological Transition and with the support of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB). This represents a significant step forward in the assessment and management of this type of environmental pollution, which has harmful effects on biodiversity, night sky quality, and human rest.

The map covers the entire territory of Catalonia for the first time, with a resolution of 1 km², and was produced using, among other resources, a high-precision scientific prediction model that is internationally recognised. To calculate the zenith night sky brightness at more than 32,000 points across Catalonia, three supercomputers were used—one of them belonging to the Consortium of University Services of Catalonia (CSUC)—amounting to more than 600,000 computing hours.

The global map of night sky brightness is now publicly available on the Department’s website and is expected to be updated with more precise data in the coming months as part of a project that will continue until 2026.

The results show that the areas with the highest levels of light pollution are concentrated along the Catalan coast, in major cities, and in the industrial zones of Barcelona, Tarragona, Lleida and Girona, as well as in certain rural areas with intense tourist activity such as Cerdanya, La Seu d’Urgell, and the Val d’Aran. In contrast, inland areas and the Pyrenees and Pre-Pyrenees, particularly regions with special light pollution protection—such as the Montsec area or the Alt Pirineu Natural Park and the Aigüestortes i Estany de Sant Maurici National Park—maintain excellent night sky quality with very low light pollution.

This new tool offers a more accurate spatial view of the current state of light pollution and, in the future, will help assess how the quality of the night sky might evolve depending on changes to public lighting, new urban developments, or the implementation of specific policies aimed at protecting nocturnal ecosystems.

Unlike other approaches based solely on satellite imagery, this project also integrates the public inventory of outdoor lighting in Catalonia, compiled by the secretariat of Ecological Transition. This allows for a much more accurate assessment of the impact across the region. The inclusion of this database meant incorporating more than 200,000 lamp and luminaire combinations into the model and was key to accurately characterising the sources of light emissions, which now account for over 1.56 million individual light points.

The map is further enhanced by real-time data from the Light Pollution Observation Network (XOCL), which is also part of the night sky quality assessment campaign. For more than a decade, this network has systematically gathered information on night sky brightness from multiple locations across the territory. This work has created a continuous database, essential for long-term analysis. Now that the data collection model is established, current efforts focus on maintaining the network, improving its connectivity, and expanding it with new measurement points.

The network is made up of various fixed sensors distributed throughout the region. These devices record zenith night sky brightness, collect data every few minutes, and automatically transmit it to a centralised management system, which receives, analyses, and processes the information to continuously assess night sky quality in real time.

The map provides a comprehensive view of the condition of the nocturnal natural environment and is available to nature conservation professionals, outdoor lighting design specialists, and the general public. It helps identify areas with the best night sky conditions, both to preserve them and to enjoy amateur astronomy and stargazing—for example, in the search for the best spots to observe the popular Perseid meteor shower (known as the ‘Tears of Saint Lawrence’) that occurs in mid-August.

The secretariat of Ecological Transition plans to allocate more than €9 million by 2028 to another project aimed at reducing the environmental impact of outdoor lighting in natural areas that are especially sensitive to light pollution. The project is funded by the Climate Fund, which is supported by 50% of the revenue from the CO₂ emissions tax on vehicles and 20% from the tax on environmentally impactful installations.

The project includes various actions to protect the most vulnerable areas from light pollution. Ongoing initiatives include:

• Implementation of the action plan for the Montsant Natural Park
• Initial works for the protection of the Ports Natural Park
• A participatory process to draft a plan for preserving and promoting the night sky of Montsec

These actions fall under the European Nature Restoration Law, which requires measures to restore habitats until they are in good environmental condition, including maintaining natural darkness and sound quality.