TreeNet meets Sentinel 2

TreeNet permanently measures growth and tree water deficit (TWD) of more than 300 tree individuals in forests all over Switzerland with so-called point dendrometers. TWD has shown to be a reasonable biological indicator for drought stress and quantifies the amount of missing water a tree needs to reach full saturation. In combination with spectral anomalies of satellite-based indices (e.g. NDWI from Sentinel 2ab) between 2018 and a reference period of 2015-2017 we would like to test whether we can (i) find a close link between the two drought stress indicators, (ii) define thresholds of TWD which are detectable from the satellite, and (iii) use this knowledge to map the impacts of the drought 2018 for Switzerland. The drought 2018 offers a unique opportunity to verify the quality of this links because of the large range of drought intensities.

Drought-indices will be calculated from the satellite images (10x10m) for those sites where the TreeNet trees are measured. Timeseries will cover very wet to extreme dry conditions.
• Cleaning and preparing TreeNet data in order to calculate the tree water deficit.
• Analyzing the combined set of data along a drought intensity gradient.
- Correlating TWD to different satellite-based drought indicators
- Optimizing the parameters of the satellite-based indicators in order to increase the fit to TWD
- Finding species-specific thresholds of TWDs that are detectable from satellite
- Producing drought stress maps of Switzerland with the merged set of tree and satellite data