## 3 Results
### Review of Thematic Foci on Extreme Weather Events and Climate Change
#### 3.6.1 Drought  
A total of 49 studies dealt exclusively with the extreme event of drought. The distribution of associated forest responses varies widely, as shown in Figure 10.  
Drought is most rarely associated with phenological changes. Three studies investigated the extent to which drought events induced early wilting. Using multispectral timeseries from MODIS and Sentinel-2, changes in the NDVI or EVI signal could be attributed to early leaf shedding [38; 116; 117]. Both [PERSON] et al. [116] and [PERSON] et al. [38] demonstrated the impact of the severe 2018 drought in Central Europe on temperate forests and the resulting early leaf shedding. While [PERSON] et al. [116] confirmed that early leaf shedding occurred during the entire study period (2017-2021), increased in extent with increasing drought intensity, and was linked to anomalously high temperatures and arid conditions, [PERSON] et al. [38] focused exclusively on the effects of the 2018 drought. Additionally, both studies demonstrated that early leaf shedding can have an impact into the next year. [PERSON] et al. [117] also reached the same conclusion for the North American temperate  
Figure 10: The relative values of the associated forest response categories differentiated by extreme weather events, recurrent extreme events, or climate change-induced trend changes, whereby the absolute figures fluctuate greatly. deciduous forest, additionally noting that moderate heat waves and drought stress resulted in delayed leaf fall. Eight of the drought studies dealt with the impact of drought on forest productivity. Common to all these studies is the use of spatially coarse resolution sensors to calculate forest productivity or biomass production [118; 119; 120; 121; 122; 123; 124; 125]. [PERSON] et al. [123] discovered that soil moisture controls productivity. They were able to show a strong correlation between soil moisture and a severe drought in China in 2022. According to this, there is a threshold for soil moisture. Below this point, forest productivity decreases distinctly. The methods and data that can be used to measure changes in forest productivity related to drought have been analyzed several times [119; 122; 125]. [PERSON] et al. [119] used signals measured using GOME-2 and OMI, as well as the flux tower, to analyze the effects of drought on photosynthesis, isoprene emissions, and atmospheric formaldehyde in mid-latitude U.S. forests, and showed that both flux-derived Gross Primary Production (GPP) and remotely sensed measurements show a reduction during drought. Using solar induced flux (SIF) measurements, [PERSON] et al. [122] were able to show that, in Europe, the effects of drought are reflected by a relatively moderate reduction in SIF. By comparing remotely sensed data with in situ data, these studies underline the potential of remote sensing to detect productivity changes. Another focus of productivity studies was the comparison of different ecosystems [120; 122]. [PERSON] et al. [120], for example determined the resilience of Spanish forests based on their productivity. It was shown that Mediterranean forests in particular have lower resilience but higher recovery compared to temperate forests in the north. Resilience, as used in this publication, refers to the framework proposed by [PERSON] et al. [126]. The term is defined as the capacity to reach pre-episode growth levels. The original methodology employed the use of tree ring data for the calculation. [PERSON] et al. [120] adapted this approach to remotely sensed data, quantifying the difference in NDVI before and after the dry year (i.e., the capacity of trees to recover NDVI values similar to those observed prior to the drought). However, the largest group (\(n=27\)) of studies with an exclusive focus on droughs refer to the mortality of a tree, stand, or forest. The focus of the studies on Germany [127; 128; 129; 130; 87; 131; 88; 132; 87; 133; 88; 134; 89; 135; 136; 87; 137; 138] and the USA [132; 133; 134; 135; 136; 137; 138] is noticeable.