The process of creating the new Climate Atlas of Catalonia (1991-2020)

Climate normals have two main functions in climate studies: (1) become an implicit predictor of the conditions most likely to be experienced in the near future at any location, and (2) be a stable reference against which to compare long-term changes in climate observations. When normals are expressed as georeferenced climate data in a regular grid, then we talk of digital climate atlases.

Here we describe the steps followed to develop the new Climate Atlas of Catalonia (1991-2020), the reference tool to provide information to the government, regional authorities, businesses and citizens about the characteristics of Catalonia's climate during the last thirty years. First, a description is made of the database used (daily mean, maximum and minimum temperature, and precipitation), which presents a much higher density of climate information than other previous periods, including data from automatic weather stations, and from high mountain and remote areas, about which there was very little knowledge of its climatology. Secondly, the quality control procedure that has been applied is detailed, and the subsequent homogeneity analysis (by means of ACMANTv5), which has made it possible to correct artificial biases in the series. Finally, the interpolation methodologies that have been tested are described, and the one that has finally been chosen for the generation of the digital cartography.

The final product includes high-resolution digital cartography (1 km for precipitation, and 100 m for temperature) at different time scales (monthly, seasonal, and annual) and for the four essential climate variables mentioned above, which will be freely available through the SIG portal of the Government of Catalonia (https://sig.gencat.cat/visors/hipermapa.html). To conclude, the work includes a comparison of the results obtained between the periods 1961-1990 and 1991-2020, making visible the warming experienced in the region and some changes in rainfall patterns.