## 2 Materials and Methods
### Selecting FLUXNET Stations for Flux Data Analysis
#### 2.2.2 Selecting FLUXNET Stations for Analysis of Flux Response to Extreme Weather Conditions  
For the selected periods, the number of months in which temperature or precipitation exceeded the 95% quantile was calculated separately for the warm (April-September) and cold (October-March) seasons. The difference between the late 20 th and early 21 st centuries is shown in Figure 3 for air temperature and Figure 4 for precipitation. The regions with a significant increase in the number of extremes are marked by an intense red color. Figure 1: Number of grid cells in the area north of 40° N of the ERA5 reanalysis where the trend turning point was detected for air temperature (**a**) and precipitation (**b**) time series. Figure 2: Number of trend turning points detected in each grid cell for the period 1979–2021 for air temperature (**a**) and precipitation (**b**) north of 40° N.  
Figure 3: The difference between the late 20 th century (1980–2000) and the early 21 st century (2001–2021) in the number of months with the temperature exceeding the 95% quantile (color) for the warm period—April–September (**a**) and the cold period—October–March (**b**). Overlaid stations are the FLUXNET stations located in the areas of maximum changes in extreme temperature (dots), which were selected for further analysis. A total of 18 flux stations from the entire global and regional FLUXNET archives (Figure 5) were selected to analyze the possible NEE and LE flux feedback of temperate and boreal forests for extreme temperature and precipitation events, corresponding to the regions with the highest increase in the number of extreme temperature (Figure 3) or precipitation (Figure 4) events over the last few decades. Furthermore, eight additional stations with very long and gap-free flux observation series and a consistently high frequency of occurrence of anomalous weather events were also chosen. All stations were assigned to 5 major vegetation types [51] according to the ecosystem classification used in the FLUXNET archives: evergreen needleleaf, evergreen broadleaf, deciduous needleleaf, deciduous broadleaf, and mixed forests (Figure 6b). The selected flux monitoring stations are associated with various climate types according to the Koppen climate classification [52] (Figure 6a). The information on the location of the flux stations, the period of observation, the types of climate, and the characteristics of the forests are summarized in the Table 1.  
Figure 4: The difference between the late 20 th (1980–2000) and early 21 st (2001–2021) centuries in the number of months with precipitation exceeding the 95% quantile (color) for the warm period—April–September (**a**) and the cold period—October–March (**b**). Overlaid stations are the FLUXNET stations located in the areas of maximum changes in extreme precipitation (dots), which were selected for further analysis. Figure 5: The FLUXNET stations of the Northern Hemisphere with vegetation types according to the ecosystem classification used in the FLUXNET archive. Figure 6: The forest stations of global and regional FLUXNET networks selected for the analysis of the flux response to extreme weather conditions. Maps of the monitoring stations are overlaid with maps of the Köppen climate classification (**a**) and vegetation types (**b**) according to the ecosystem classification used in the FLUXNET archive. The color of the circles correspond to the forest types, the number inside the circle—to the number of the monitoring station (Table 1). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sations** & **Long. Lat** & **Elev.