## 3 Results
### Sif\({}_{757}\) Response during the 2015/2016 El Nino Drought Event  
We found different drought effects across the Amazonian MBF-ER in the Amazon basin during the El Nino 2015-2016 peak (Figure 4A,B; Appendix A Table A2). The drought indicator clearly captured an increased VPD and increased temperature values across the KG zones and ER. Our analysis of the SIF\({}_{757}\) variations during the CARA period in the Af, Am, and Aw climate zones showed a net change of \(-\)2.42%, \(-\)1.46%, and \(-\)1.42%, respectively (Figure 4A). For the ER, we estimated that the drought effects varied from \(-\)31.09% (ER 7) to +17.56% (ER 32) during the El Nino 2015-2016 drought peak. We assessed 21 MBF-ER and found that 8 ER showed a decrease in SIF\({}_{757}\) below \(-\)5% under moderate and severe/extreme drought conditions (Figure 4B; ER 2, 4, 7, 8, 15, 25, 29, 31), although the fPAR increased in four of these cases (ER 7, 4, 25, and 15). Drought areas yielded SIF\({}_{757}\) increases above 5% at 4 ER (1, 18, 32, and 6). We found an increased IQR for the temperature values in all ERs except for ER 9 and 18. Moreover, we also observed increases in the VPD in all ERs under drought except for ER 15, 9, 5, and 18.  
Figure 3: **(A)** The number of months and **(B)** the area in km\({}^{2}\) in which pixels meet different drought indicators thresholds during the period from September 2014 to December 2016.  
Figure 4: (**A**) Time-line of the MBF-SIF\({}_{757}\) from three KG-climate zones during the climatological  
and rain anomaly period (CARA; see methods). Shown are the standard error and the estimated \(\text{SIF}_{757}\) variations for each time-step. The red dashed lines mark the stages of the CARA period. The red and blue barplots show the \(\text{SIF}_{757}\) increases and decreases during the CARA period based on the percentual change in respect to the baseline period (Equation (2)). (**B**) Surface temperature and vapor pressure deficit (VPD), as well as the percentage change in the \(\text{SIF}_{757}\) and fPAR in 20 ecoregions (ERs) during the El Nino 2015-2016 peak. (**C**) Spatial distribution of the estimated vulnerability of \(\text{SIF}_{757}\) when affected by El Nino 2015-2016 peak drought conditions. The vulnerability was estimated as the difference between the means of \(\text{SIF}_{757}\) in non-drought and droughted pixels per ER over a 6-month yearly phenological period of 2.5 years. The inserted pie chart shows the proportional share of the vulnerable ER within the MBF biome (5,223,985 km\({}^{2}\)).  
The overall results indicate that the largest net MBF-\(\text{SIF}_{757}\) change occurred in the Af climate zone. However, the analysis that also considered drought sub-regions indicated that the most notable \(\text{SIF}_{757}\) decreases in vegetation occurred in the Am and Aw climate zones (Figure S3). Moreover, a higher spread of the time-step means was observed in the Am and Aw climate zones under moderate and severe/extreme drought than that under non-drought conditions compared to Af.  
Figure 4C shows a drought vulnerability map across the Amazonian vegetation ecosystems including their \(\text{SIF}_{757}\) values. All values used for the drought-peak estimation, the number of retrievals, and the area of each ER are presented in Appendix A Table A2. The drought effects on \(\text{SIF}_{757}\) could not be quantified due to the absence of moderate, or severe and extreme droughted retrievals at ERs 11, 13, 17, 21, 23, and 24 (the black areas in Figure 4C).