Autumn in Spain could change considerably over the coming decades. Summers are getting longer and the temperatures typical of this season are maintained for longer, even when the calendar already announces the arrival of the cold. Meteorological records confirm this evolution and suggest that climate change is modifying the duration of the seasons as we know them.
According to analyzes by the State Meteorological Agency (AEMET), summer is lengthening in Spain at an approximate rate of nine days per decade since the 1980s. If this trend continues, in just 20 years it could add between 18 and 20 more days. A transformation that would especially affect autumn, which would lose part of the period in which we traditionally enjoy cooler temperatures.
Summer in Spain lengthens nine days per decade and threatens autumn
Meteorological data show that summer is gaining ground on other seasons of the year. AEMET has been studying this evolution for some time and has published different analyzes on how temperatures have changed in Spain during recent decades.
One of them, prepared by meteorologist Benito Fuentes López and published on the agency’s official blog, used data from the ERA5 reanalysis of the European Copernicus service to study the evolution of summer between 1940 and 2023. The results showed that, on average, summer currently lasts about a month longer than in the past.
The increase is not the same throughout the territory. According to the analysis, the lengthening is especially pronounced in the east and northeast of the peninsula, where in some points it exceeds a month and a half. On the other hand, in much of the western half the increase is smaller.
The phenomenon has two aspects: spring, when the summer heat comes before spring, and summer, when summer temperatures last into autumn.
In the latter case, the AEMET study indicates that the trend is less clear. On the Cantabrian and Mediterranean coasts an extension of approximately two or three weeks is observed, while in much of the western peninsula it does not usually exceed one week.
Added to these data is a more recent analysis by the agency, which places summer growth at around nine days per decade since the 1980s. If that pace is maintained, the station could gain an additional 18 to 20 days over the next two decades.
In 20 years, autumn could lose days to summer
What would happen if summer continues to lengthen at the current rate? The answer is related to the distribution of the days that this station wins. If heat is brought forward in the spring and delayed in the fall, both transition seasons lose part of their thermal duration.
According to the information collected by AEMET, of the 27 days that summer could gain in three decades, approximately 15 would come from autumn and the rest from spring.
Applying that same proportion to the next 20 years, autumn could lose about ten days. It is a mathematical estimate based on the observed trend, not an official agency prediction or a guaranteed date for the future.
This helps understand why meteorologists warn that autumn could be shortened and delay the arrival of the conditions typical of this season. In certain areas, temperatures that were previously common in September and October could be maintained for longer, causing the autumn atmosphere to be perceived later.
However, the change will not be identical in all autonomous communities. The geographical location, the influence of the sea and the climatic characteristics of each region determine the evolution of temperatures.
Climate change is also modifying the seasons in Spain
The lengthening of summer is related to global warming. The increase in average temperatures makes warm episodes more frequent and the conditions typical of summer are maintained for longer periods.
AEMET’s climate balance for 2026 offers a recent example of this evolution. The average summer temperature in mainland Spain reached 24.5 °C, that is, 2.4 °C above the average for the period 1991-2020. It was the warmest summer in the official series, which begins in 1961.
Furthermore, fully summer conditions lasted for four months, from the second half of May to the first half of September, approximately one month longer than the usual duration of the season on the calendar.
This change does not only affect the thermal sensation. It can also have consequences for ecosystems, as temperatures influence plant flowering, leaf fall, animal reproductive cycles, and insect activity.
For example, a warmer autumn can delay some vegetation processes and modify the water needs of certain species. It can also alter the activity and migration rhythms of some animals, which depend on environmental conditions to complete their biological cycles.
Of course, there is an important difference between astronomical stations and thermal stations. Astronomical autumn will continue to begin with the September equinox and end with the December solstice. In 2026, it started on September 23 and will end on December 21.
Therefore, autumn will not disappear from the calendar or officially begin in November. What is changing is the behavior of temperatures: summer is gaining ground and the period of time in which we experience a truly autumnal atmosphere could be increasingly shorter.
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