The number of summer days has increased from 90 to 145, in the last 50 years, according to a UPC study

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A study by the Centre for Land Valuation Policy (CPSV) at the UPC analyses the average increase in temperature and heat waves in the main cities of Spain.

The average increase in temperature was 3.54°C between 1971 and 2022. Over these last 50 years, summer days have increased from 90 to 145, which represents a two-month increase in hot days. Tropical nights have gone up by 18 from an average of 45 to 63.

The year 2022 was the second warmest on record in Europe, at 0.9°C warmer than average. In many countries in southwestern Europe, it was the warmest year on record. The highest anomalies in temperature occurred in northeastern Scandinavia and in the countries bordering the northwestern Mediterranean Sea.

The Mediterranean is considered one of the regions that is most vulnerable to climate change in the twenty-first century. The mean temperature over the Mediterranean has been increasing above the global average and is a key factor in explaining the increased temperatures in Spain. In fact, the Spanish coast, which has experienced increases of over 2°C in recent years, is one of the climate change hotspots within the Mediterranean area.

The Centre for Land Valuation Policy (CPSV) at the Universitat Politècnica de Catalunya - BarcelonaTech (UPC), linked to the Barcelona School of Architecture (ETSAB), has analysed the warning process in the main Spanish urban areas since unified records started at the start of the 1970s. To achieve this, a method was developed that was used to analyse the evolution in temperatures between 1971 and 2022 in 21 meteorological stations that are representative of all Spanish autonomous communities: Barcelona (data collected at the meteorological stations of the Fabra Observatory and the Prat Airport), Madrid (data gathered in the Retiro Park and the airport), Valencia, Zaragoza, Seville, Málaga, Bilbao, Valladolid, Ciudad Real, Badajoz, Asturias, La Coruña, Ourense, Murcia, Logroño, Palma de Mallorca, Las Palmas de Gran Canaria and Santa Cruz de Tenerife.

Results and impact

According to the results of the study, the increased temperatures, especially in extreme events such as heat waves, not only cause discomfort but also pose a significant risk to health. The information provided by the MoMo database shows that in the summer of 2022 there were 22,249 additional deaths compared to expected mortality, of which at least 4,732 were due to high temperatures.

The results indicate that the average maximum temperature in the main cities of mainland Spain rose by 2,31°C. The average minimum temperature increased by 2,26°C. In general terms, 2022 was the warmest year on record. The research that was carried out shows that the continental influence is mainly seen in the increase in maximum temperatures, while in the Mediterranean area the rise in minimum temperatures is steeper (with a greater impact on mortality). In contrast, on the Cantabrian or Atlantic coasts and, above all, in the Canary Islands, there have been less pronounced increases of below 2°C.

The increase in daytime and night-time temperatures between 1971 and 2022 in the cities that were studied is higher than the Mediterranean average.

Palma de Mallorca and Barcelona (daytime and night-time), Murcia (daytime), and Ciudad Real, Zaragoza and Madrid (night-time) have recorded the highest temperatures.

The study also presents the daytime heat waves (DHW) and night-time heat waves (NHW) experienced in the cities under study. Given the lack of consensus on how to define heatwaves, two complementary methodologies were used. First, the general criteria used by the Spanish State Meteorological Agency (AEMET), corrected to differentiate between DHW and NHW, defines a heat wave as an episode of at least three consecutive days with temperatures above the 95% percentile for the months of July and August in the reference period (1971-2000). Second is the method developed by the CPSV of the UPC, which enables heat (and cold) waves to be differentiated for daytime and night-time throughout the year.

NHW have risen from 2.7 in the decade 1971-1980 to 6.8 (1981-1990), 8.8 (1991-2000), 20.7 (2001-2010), 25.7 (2011- 2020) and 30 in the decade 2013-2022. The study shows that the increase in NHW was clearly greater than that of DHW.

The CPSV method confirms the increase in heat waves over the last 52 years. In total, 2,491 DHW were identified for the 21 meteorological stations, with a total of 10,348 proportionally high heat days associated with them. This represents a 6.98-fold increase in DHWs between the decade 1971-1980 and 2013-2022 (and a 9.48-fold increase in hot days). A total of 2,732 NHW were detected at the analysed stations and increased to 11,469 hot nights, which represents a 10.83-fold increase in NHW between the decade 1971-2000 and 2013-2022 (and a 12.94-fold increase in hot nights).

Considering the 21 meteorological stations that were studied, summer days (TX >= 25°C) have risen from 90 in 1971 to 145 in 2022. This represents a two-month increase in summer days. In turn, tropical nights (TN >= 20°C) increased by 18, from an average of 45 in all of Spain in 1971 to 63 in 2022.

In the 1971-2022 period, climate anomalies were much more pronounced (1.49°C) in Spanish cities than they were on a global scale (0.71°C). Experts warn that global warming is wreaking havoc on the main urban systems in Spain.

The study ‘Global Warming in Spanish Cities’ by the CPSV was presented at the General Assembly 2023 of the European Geoscience Union (EGU), which took place in April in Vienna.



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