Why do the leaves change color in autumn?
With the natural phenomenon of leaf discoloration, trees prepare for the cold season. The decreasing length of the day and the gradual drop in temperature trigger an ageing process in the leaves. Nutrients are broken down and chlorophyll – the green pigment in the leaves that is responsible for photosynthesis. Broken down into its building blocks and stored in branches, the trunk and the roots. As soon as the chlorophyll has disappeared from the leaves, other color pigments become visible. The two most important are carotenoids (yellow and orange) and anthocyanins (red), which provide the autumn colors. You can find more information about this in our weather lexicon at
leaf discoloration
.
Discolored leaf of a Persian beech
Discolored leaf of a Persian beech. (Source: D. Ulrich)
Weather-related causes of leaf discoloration
As mentioned above, the two main factors for leaf discoloration are the shorter day length and the drop in temperature. But there are other factors that have a significant influence on the intensity of autumn discoloration, most notably soil moisture. Dry and hot summers cause drought stress in the vegetation and result in some of the india mobile database foliage drying out. The foliage quickly turns brown and the leaves fall off prematurely, as was the case in many places in 2022 and 2023, for example. Strong winds and early frosts can also play an important role and accelerate leaf fall, thus reducing the duration of leaf discoloration.
Larch forest in Thyon
Larch forest in Thyon. (Source: D. Ulrich)
What will it look like in autumn 2024?
This year, all the factors are in place for a high intensity of autumn colours. There was best free wp rocket alternatives repeated rainfall throughout the year, Switzerland experienced no major storms in October – apart from the foehn valleys – and temperatures remained high, ie no severe frost was observed in the lowlands and at medium altitudes.
Attached is a compilation of pictures that we have received in the last few days via the MeteoSwiss app. The magical autumn landscapes in Switzerland are in no way inferior to those in North America.
The Sun as a Spoilsport
In order to fully enjoy the autumn colours, the only thing that ultimately prevented us be numbers from doing so was the lack of sunshine. Dry and sunny periods have been rare in recent weeks (see
blog from October 21st
).
After a cloudy Wednesday, things are looking up, especially in the mountains. On Thursday and Friday, it will be quite sunny at higher altitudes and the autumn colours can be admired in all their glory. In the lowlands, however, fog and high fog are likely to make for grey weather, at least in the first half of the day. The air is also more humid directly on the Alpine ridge and on the southern side of the Alps, and the sun is having a hard time shining.