As a result of past drought summers (e.g. 2003, 2015, 2018), an increased dieback in various tree species was observed in Germany and Europe (references 1-3). In this context, the Forest Condition Monitor (FCM) is supposed to visualise the condition of forests in Germany and Europe. In order to make this possible, remote sensing data will be used to determine the greenness of the vegetation and compare it with long-term observations. To illustrate both the relative and absolute variation of greenness over the observation period, the FCM currently offers 2 products:

The quantiles allow to illustrate the ranking of the greenness observations. Thus, it can be determined how the greenness behaves to a selected date relative to all other years. The main objective of the quantiles is the representation of positive and negative extreme values, which can indicate particularly favourable (early spring, sufficient precipitation) or unfavourable (drought, late frost, calamities) environmental conditions. On the other hand, the proportional deviations represent the absolute deviation of the greenness from the long-term mean value in percent.

The complementary products on the one hand reveal insights on extreme green values (such as in 2018 and 2019) since 2003 (quantiles) and, on the other hand, allow for classifying these extremes (proportions). The latter is particularly necessary in areas with a low overall variability, where even small deviations from the long-term average are classified as extreme values.

Greenness is estimated using the NDVI (Normalized Difference Vegetation Index), which has been used earlier to quantify the impact of extreme weather events on vegetation (references 4-7). The NDVI makes use of the surface reflectance in the red and near infrared spectrum. Photosynthetically active, vital leaves feature a higher reflectance in the near infrared range compared to red wavelengths. For this reason, healthy leaf mass appears to our eye in a green color. Dying leaves, on the other hand, have a clearly increased reflectance in the red spectral range, which is why this appears to our eye in different orange, red and brown tones.

The spectral information on which NDVI is based is obtained by the two MODIS satellites (MODerate resolution Imaging Spectrometer) with a spatial resolution of 231 m x 231 m and a time interval of 8 days. Due to the spatial resolution of 231 m x 231 m, the interpretation of the values should be cautious with regard to small-scale processes (e.g. death of individual trees). Further details on the interpretation can be found on the individual product pages.

A detailed methodological description along with application examples is given in reference 8.

A brief introduction video is available here.

Due to possible artefacts in the input data (e.g. due to atmospheric disturbances or influence of other vegetation components) the forest condition monitor does not guarantee individual values. Nevertheless, the values shown correspond well with ground-based observations (see also descriptions of the products).