Global Warming in Spanish Cities (1971-2022)

According to NASA's temperature record, Earth in 2021 was about 1.1 degrees Celsius warmer than the late 19th century average, the start of the industrial revolution. The rate of Global Warming (GW), however, differs across different regions of the planet. The Mediterranean is one of the "hotspots" of climate change, with more prominent temperature increases throughout the 20th and 21st centuries (Giorgi 2006). Since the mid-20th century, the average temperature over the Mediterranean has been increasing above the global average. The recent temperature record reveals an annual mean temperature for the entire basin that is approximately 0.4°C above the global mean (Lange 2021). This increase is even higher on the Spanish coast, which has experienced increases of more than 2°C (Arellano 2022).

The aim of this paper is to analyze the warming process in the main Spanish urban areas since unified records were kept in the early 1970s. For this purpose, the evolution experienced by temperatures between 1971 and 2022 in 21 meteorological stations representative of all the Spanish Autonomous Communities is analyzed. Barcelona, Madrid, Valencia, Zaragoza, Seville, Malaga, Bilbao, Valladolid, Ciudad Real, Badajoz, Asturias, Corunya, Ourense, Murcia, Logroño, Palma de Mallorca, Las Palmas de Gran Canaria and Santa Cruz de Tenerife, are studied.

The results show that, if on a global scale temperatures have risen 0.94°C since 1971, the increase in the main cities of peninsular Spain has been 2.17°C. And 2022 will be the warmest year on record. The research carried out differentiates the evolution experienced by maximum and minimum temperatures, showing that the continental influence is mainly manifested in the increase of maximum temperatures, while in the area of Mediterranean influence, the increase of minimum temperatures is more pronounced. On the other hand, the Cantabrian and Atlantic coasts, as well as, above all, the Canary Islands, show less pronounced increases, below 2°C.

The study also presents the heat and cold waves (Serra 2022) experienced by the cities studied. Diurnal heat waves (DHW) have increased from 0.6 per year per weather station in the decade 1971-1980, to 1.71 in 1981-1990, 1.81 in 1991-2000, 2.72 in 2001-2010, and 3.84 in 2011-2020. 2022, with 7.11 DHW per station, is the year with the highest number of diurnal heat waves in the entire series. Regarding nocturnal heat waves (NHW) they have increased from 0.47 per station per year in the decade 1971-1980, to 1.53 (1981-1990), 1.57 (1991-2000), 3.55 (2001-2010), and 4.63 (2011-2020). Again 2022 is the year with the highest number of NHW, with 7.61 per weather station.

2022 appears, therefore, as the warmest year since records have been kept, and the one in which a greater number of NHW has been experienced.