How we do:
In order to calculate the temperature for each of the beaches, PÚBLICO used two databases: the list of beaches, and their respective geographic coordinates, provided by the Portuguese Environment Agency (APA) and the ocean surface temperature data extracted from prediction and analysis systems for the Portuguese coast (mainland and islands) from the Copernicus Marine Environment Monitoring Service.
The geographic coordinates of the beaches in the APA database were used to identify corresponding points in the Copernican ocean surface temperature records. For mainland Portugal and the Madeira archipelago, the Iberia-Biscay-Ireland system was used, based on an ocean model that assimilates local and satellite data to carry out temperature forecasts and analysis, among other indicators. For the Azores archipelago, the global oceanic analysis and forecast system was used.
For each of the beaches, the sea temperature forecast for the day is collected daily, between 8am and 8pm. These records are contextualized with a historical comparison that considers the average sea water temperature on all beaches between 1993 and 2021. This value was obtained through a lengthy process of collecting hourly data for all these points, followed by the calculation of the averages and respective standard deviations for each of the beaches.
