Beech forests in autumnBeta

Beta analysis: we measure the colour of the beech forests from the satellite and are still validating it. If you are at Tejera Negra or Montejo, a photo from today helps us check it: send it to hola@cuandoflorece.es with the date and place.

Every few days we follow the colour of two beech forests in the Sierra de Ayllón with the Sentinel-2 satellite and compare it with what is usual since 2017. On the right, what is going on, written from the data.

0 % = this summer's green; 100 % = the usual peak colour. Line: median of the areas we watch; shading: the middle half of them. Yellow lines: usual date of each milestone; red: today. Bands: weather episodes.

Tejera Negra

Colour begins (20 %)
Seen on 4 Sept · check
Usually: 7 Oct (19 Sept to 25 Oct)
Colour well advanced (50 %)
Not yet
Usually: 14 Oct (28 Sept to 30 Oct)
Peak colour (80 %)
Not yet
Usually: 19 Oct (6 Oct to 19 Dec)

What is going on

Last clear pass: 24 Sept · colour 25 % · 7 areas

The colour begins on 4 Sept came far earlier than any year since 2017 and coincides with the heatwave from 3 Sept to 5 Sept (máx. 30 °C): it may be leaves scorched by heat or drought, not autumn colour.
Since then the index has fallen from 39 % to 25 %: autumn colour does not go backwards, which suggests it was not autumn.
The other forest went through the same heat (máx. 32 °C) without changing colour: this one is more sensitive, or something else is going on.
When we will know more: around 19 Oct. If it is autumn, the index will rise steadily towards 50 %; if it stays flat or falls, the heat brought forward the loss of some leaves.

The weather this summer and autumn

Heatwave: 12 Aug – 14 Aug · máx. 30 °C
Heatwave: 3 Sept – 5 Sept · máx. 30 °C

Weather: Open-Meteo, at the centre of the watched areas.

Montejo

Colour begins (20 %)
Not yet
Usually: 28 Oct (18 Oct to 9 Nov)
Colour well advanced (50 %)
Not yet
Usually: 6 Nov (26 Oct to 12 Nov)
Peak colour (80 %)
Not yet
Usually: 10 Nov (2 Nov to 13 Nov)

Summary

As of 26 September 2026.

Tejera Negra: the index jumped to 39 % on 4 Sept, right during a heatwave, and has fallen since. It looks like scorched leaves, not autumn; we will confirm it around 19 Oct.

Montejo is still green; colour usually begins around 28 Oct.

Cuándo Florece's own analysis using Copernicus Sentinel-2 (ESA) data and Open-Meteo weather. Beta.