How long autumn lasts can actually be read in the calendar. It begins next Wednesday in 2021 and ends three months later, because winter begins on December 21.
But how long autumn lasts in nature is another matter. This can be seen in the ripening and decay of the flora. That is what the science of phenology studies. Their basis: In order to determine a good time for sowing and harvesting, people have always observed nature, such as flowering, fruit ripening and leaf fall of certain plants. The hazel blossom marks the beginning of early spring. Overall, the phenology comes to ten seasons because it divides spring (early, first, full spring), summer (early, high, late summer) and autumn (early, full, late autumn) into three phases each. The winter when nothing grows is just winter.
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“Compared to the period 1961 to 1990, the beginning of the phenological seasons from early spring to early autumn has moved forward by around two weeks over the past 30 years,” explains Andreas Brömser (39) from the German Weather Service. “This is due to the higher average temperatures caused by global warming.” On the other hand, the beginning of late autumn with the leaf discoloration has shifted backwards. Overall, this means a longer autumn: “Since the fruit ripening of the elder at the beginning of the early autumn is on average twelve days early and the leaf fall of the pedunculate oak is slightly late towards the end of the autumn, the phenological autumn has become around two weeks longer.”
Spring and summer also got a little longer – at the expense of winter. It has shrunk by 19 days on average.