Summer is, in general, a very pleasant time: it is time for vacations and travel, relaxation, beach and mountain, to spend more time with family and friends … but sometimes the thermometers go off and the heat makes us pass very bad times.
How do we define a heat wave? It is not an easy task, since what we call “heat” is very relative depending on what area we are in. For example, it is very likely that in Belgium they call “hot” a summer day in which the temperatures exceed 30 ° C, while in Seville that is normal. In addition, temperatures are not the only factor to take into account when talking about heat waves: the duration and number of affected localities are also decisive.
Considering all these variables, the State Meteorological Agency (AEMET) defines a heat wave as “an episode of at least three consecutive days , in which at least 10% of the stations considered register maximums above the 95% percentile of its series of daily maximum temperatures for the months of July and August of the period considered “. When calculating the 95% percentile, what is actually done is to locate, within the time interval studied, 5% of the warmest days, and the lowest of the maximums recorded on those days is taken as the “threshold temperature”.
Since 1975 (when the AEMET records begin), practically every year a heat wave has been recorded. The last one was during the summer of 2018 and the most remarkable thing about it is that it affected 36 provinces on August 3 , which turned out to be the warmest day. The first wave of the summer of 2019 began on June 26 and is expected to affect a large part of the Iberian Peninsula and the Balearic Islands.
But let’s see what the worst heat waves in recent years have truly been:
2017, the summer with the most heat waves
During 2017, the record for the number of heat waves was broken, surpassing that of 1975. These occurred between June 13 and August 22 , divided into five episodes, one every 18 days. The episodes have occupied almost a whole month of the summer season, 25 days under the umbrella of a heat wave. The AEMET declared that this summer it exceeded the heat waves of 1991 and 2016, having a longer duration and generating higher temperatures distributed throughout the Peninsula.
The highest absolute temperatures arrived during the second wave , on July 13 in all the points of the 14 affected provinces with an anomaly of 3.9 degrees, a value only exceeded in 1987. In Granada / Airport they reached 45.7 degrees , in Jaén 44.4 and in Córdoba / Airport 46.9 degrees were reached. Of the five heat wave episodes suffered, the third and fifth presented an anomaly of 1.6 and 2.2 degrees respectively, which is why they were the least remarkable moments of the summer.
The terrible summer of 2015
We still have fresh in our memory – although perhaps that adjective is the least indicated to talk about heat waves – the summer of 2015: it was the longest heat wave recorded in our country in the last 40 years, as it lasted from 27 June to July 22. For almost a month the heat gave us no respite either day or night: the warmest day was July 6, with a maximum temperature of 37.6 ° C. It must be taken into account that this value is an average of all the localities, and that in many parts of the peninsula much higher temperatures were reached, as the attached map shows. In fact, 40 ° C was exceeded in practically the entire territory except for the northwest quadrant, and the thermometers reached 45.2 ° C at the “Córdoba airport” meteorological station and in Montoro, also in said province.
The minimums were also anything but low: they exceeded 20 ° C in almost all regions, and in areas of Andalusia, Ciudad Real, Albacete, Murcia, Alicante, Tarragona, Barcelona, Lleida, Huesca and the Balearic Islands, the thermometers did not drop below 25 ° C, making it quite difficult to fall asleep.
During the 26 days that the heat wave lasted, there were only two in which the thermometers gave a little respite, specifically on July 2 and 11, although there were areas in which it was practically not noticed and in any case it did not reach be enough to interrupt the heat wave. The regions in which it was felt with the least intensity were Galicia, Asturias, Cantabria and the Basque Country.
The 2003 heat wave
More distant is the summer of 2003, and the heat wave suffered during it also lasted somewhat less, specifically from July 30 to August 14, although it is the second longest after last year. It also stands out for the number of affected provinces , 38, and it is also the case that the whole summer as a whole was the warmest since there are records, with an average temperature of 24.94ºC at the national level.
The third wave highlighted by AEMET lasted 4 days and occurred between August 8 and 12, 2012. It was the most intense in terms of number of affected provinces, forty, and the warmest day was August 10 , with a “maximum temperature of the wave” of 39.5 ° C. In addition, the threshold temperature was exceeded in almost all the regions analyzed, so the wave was generally perceived as especially intense. In meteorological stations such as Seville airport , 45.9 ° C was exceeded.
Source: State Meteorological Agency
