“Forget about the Iberian peninsula,” concluded a renowned German atmospheric physicist, Hans Joachim Schellnhuber, in view of the extreme heat that the south of Europe will have to bear in the not-too-distant future. Dominic Royé, a climatologist, postdoc researcher and lecturer at the University of Santiago de Compostela in Spain’s Galicia region, quotes Schellnhuber when discussing his latest article on heatwave projections, co-authored by Nieves Lorenzo and Alejandro Díaz-Poso and published in the scientific journal Atmospheric Research. The article indicates a significant increase in the intensity, frequency, duration and impact of these extreme heat episodes; it is predicted that the number of heatwave days will double less than 30 years from now.
According to Rubén del Campo, spokesperson for the Spanish weather agency Aemet, “the worst summers so far will be normal for our grandchildren and will even be considered cool by their children.” In the southern city of Córdoba, for example, where Spain’s highest ever recorded temperature was measured at 46.9ºC in 2017, there will be five days a year at 47ºC or 48ºC. These are temperatures typical of Iraq.
But what is considered a heatwave? “There is no universal definition,” says Royé. The World Meteorological Organization defines it as unusually warm weather that persists for at least two days with temperatures above the usual threshold. In Spain, Aemet states that a heatwave is when temperatures range within the 5% of hottest days recorded in at least 10% of the weather stations over three days. Royé and his colleagues do not apply the Aemet definition but instead refer to a recently created index called Excess Heat Factor (EHF), which establishes that there is a heatwave if the 95th percentile of the highest average temperature is exceeded for three days. Developed by Australian scientists, the EHF takes another factor into account: acclimatization or heat adaptation. “This index considers whether it was hotter than average in the 30 days prior to the heatwave, because if an extreme heat event happens suddenly, it produces more stress and more impact,” says Royé.
Royé, Lorenzo and Díaz-Poso’s calculations focus on two scenarios between 2021 and 2050, one being the worst-case scenario, the other being an intermediate scenario, based on projections of what happened during the reference period of 1971 to 2000. According to Del Campo, whatever we do to reduce emissions, the impact on the temperature in degrees will be small until the middle of the century. The projections for Spain in both scenarios predict an increase towards the middle of the century of 1.5ºC or 2ºC, but from then on the difference between the two scenarios becomes more evident. For example, by 2050, the maximum summer temperatures will be 2ºC hotter in the intermediate scenario, and 3ºC hotter in the worst-case scenario. But in the last two decades of this century, the increase ranges from 3ºC in one scenario to 6ºC or 7ºC in the other.
These temperatures are a throwback to the summer of 2003, the hottest so far in Spain and Europe, when the average temperature was 2.5ºC above normal. The brutal heatwave exacted an excess death toll in Spain of 6,600 people in just 15 days – 140 dying directly of heatstroke; in France, the death toll reached 14,500.
By the end of this century, in the worst-case scenario, cities such as Córdoba will experience five days every summer at 47ºC or 48ºC. In Seville, heatwaves will see temperatures of 46ºC and 47ºC, and Madrid will experience 43ºC to 44ºC, up from a record 41ºC; in Zaragoza, top temperatures will reach 45ºC or 46ºC, up from the all-time high of 44.5ºC. “These are absolutely extreme and unprecedented temperatures for Spain and typical of Iraq, Saudi Arabia, Pakistan and the west of India,” says Del Campo, adding that during a heatwave, temperatures could exceed 50ºC. Although these temperatures “are far from unlivable in for humans, they do indicate an unfamiliar climate with frightening features,” he adds.
According to the researchers behind the new projections, heatwaves at currently unimaginable temperatures will increase throughout the Iberian peninsula in both scenarios by an average of 104% by 2050, although in the mean scenario the increase will be more acute in the center and east of Spain, with a 150% rise on the Mediterranean coast and the Pyrenees. As a result, the 23 heatwave days recorded every year between 1971 to 2000 will number 40 this summer, and 53 by 2050 in the intermediate scenario, or 70 in the worst-case scenario.
The duration of heatwaves also shows an increase of more than 15 days in the Mediterranean region and a minimum of six in the northern and western regions. In addition, in the worst-case scenario, prolonged heatwaves of more than 10 days are expected practically everywhere across the Iberian peninsula, except on the Atlantic coast, where they will not exceed six or seven days. Regarding temperatures, in the reference period they were 11ºC higher than normal, a figure that will reach 21ºC higher than normal in the mean scenario and 24ºC in the worst-case scenario. And not only will there be more days of extreme heat, but they will also affect a wider area: the heatwaves’ reach will increase by 6% to 8% per decade, which means greater human exposure, greater energy demand and greater risk of fires, according to Royé.
In the reference period, heatwaves affected a maximum area of 49%, but in the predicted intermediate scenario this rises to 78% and in the worst-case scenario to 80%. In the latter, the heat events affect practically the entire peninsula, except for a narrow strip along the Atlantic and Cantabrian coasts in the north and the Cádiz area in southern Spain. The projections by these scientists indicate that the areas with the most intense heatwaves do not coincide with those experiencing the longest duration. “In Galicia and Portugal, they are very intense but brief, while in the Mediterranean they are less intense but longer,” according to the researchers.
Del Campo sees these conclusions as consistent with both the projections handled by the Spanish weather agency and with observed data, which shows that heatwaves have doubled in the last decade, going from 11 or 12 per decade to 24. “In the 1980s and 1990s, we had six heatwave days a year and in the past decade this rose to 14 days a year,” he says. Last summer, there were three heatwaves amounting to a total of 18 days. This new study “confirms that heatwaves are increasing and will increase to a greater extent in the future.”
English version by Heather Galloway.