Understanding the Magnification of Heatwaves over Spain: Relevant changes in the most extreme events

Heatwaves (HW) are a growing climate change-related risk affecting people's lives every year. A consensus exists about the magnification of this phenomena under climate change; however, less is known about their regional-tolocal evolution characteristics' undermining appropriate policy and preparedness actions. This study investigates, from 1951 to 2019, regional changes in the occurrence and characteristics of HWs over peninsular Spain and the Balearic Islands (PSBI), highly exposed to climate change. State-of-the-art high-resolution observations provided by the SPAIN02 gridded data set are used for this purpose. Our results show an indisputable magnification of the HW phenomena but with relevant regional differences in the evolution of their characteristics. HWs occur two times more frequently inland, while most intense events take place in coastal areas. More extreme HWs in terms of frequency, maximum intensity, duration, and spatial extent are identified, rather than a progressive intensification in time affecting all HWs population. In the last decades, high frequencies are 8 times more likely, unprecedented high intensities are registered, the yearly maximum spatial extent is larger than ever and the probability to have a long-duration event has doubled. All of this is in the context of a longer HW season, increasing at a rate of about 4 days/decade, particularly in its onset. About 75% of the most severe and impactful HWs occurred after 1985. The most severe HWs, generally, are found not to be the most harmful to human health. This study highlights the importance of detailed knowledge of the spatiotemporal characteristics of HWs to accurately inform local practice for the effective design and implementation of adaptation plans.