## 4 Conclusions and Discussion
(2018) applied SIF to quantify the impact of the 2015/2016 El Nino drought in Amazon and found that SIF was strongly inhibited over areas with anomalously decreased soil moisture and high temperatures. The strong El Nino event also had substantial impacts on the variations of atmospheric CO\({}_{2}\) at global and regional scales. Previous studies [PERSON] et al. (2018); [PERSON] et al. (2018); [PERSON] et al. (2018) have demonstrated that the terrestrial tropics dominated the interannual variability of the global carbon cycle. Based on the simulations from global terrestrial biosphere models, [PERSON] et al. (2018) showed that global photosynthesis decreased in 2015 and the decrease in GPP led to 60% of the net ecosystem productivity (NEP) reduction. Since El Nino affected mainly on tropical ecosystems, the growth rate of CO\({}_{2}\) in 2015/2016 was higher than the average of previous decade [PERSON] et al. (2018). When the 2015/2016 El Nino events and the fire in Indonesia occurred, tropical Asia experienced severe losses of SIF and GPP, along with increased carbon release [PERSON] et al. (2018). Our results demonstrated that the XCO\({}_{2}\) had a strong negative correlation with SIF, indicating the carbon emission in Southeast Asia during 2015 and 2016 (Figure 9). The satellite SIF data can indirectly reflect the regional CO\({}_{2}\) variations, especially when the vegetation experienced environmental stresses. Water stress usually results in the stomata closure for plant, then makes photosynthesis slow down and reduces the absorption of atmospheric CO\({}_{2}\) [PERSON] et al. (2018). Therefore, satellite SIF can be used to estimate the variations of atmospheric CO\({}_{2}\) growth rate during the extreme climate events. In summary, we found that space-borne SIF observations had great potential for monitoring the spatial and temporal response of plant growth to drought in general, with El Nino event as an example. The EVI was not able to capture the negative response of the vegetation to drought. However, satellite SIF data had more pronounced responses to extreme events than EVI when the drought occurred. Moreover, compared with SIF, SIF\({}_{\text{yield}}\) can provide more accurate information about vegetation conditions during the drought period as it removed the effects of APAR. This study indicated that satellite-based SIF reasonably characterized the spatial and temporal dynamics of drought development in crop and forest regions in Southeast Asia. Responses of vegetation photosynthesis and greenness decoupled in this extreme drought, indicating that satellite-based SIF products would be a better choice for the response of vegetation to extreme climate events induced by the strong El Nino events in the future. Conceptualization, Y.Z. ; Data curation, X.Q. ; Formal analysis, X.Q. and B.Q. ; Investigation, X.Q. ; Methodology, B.Q. and Y.Z. ; Software, X.Q. ; Supervision, Y.Z. ; Writing--original draft, X.Q. ; Writing--review & editing, B.Q. and Y.Z. **Funding:** This research is financially supported by the International Cooperation and Exchange Programs between NSFC and DFG (41761134082) and General Program of National Science Foundation of China (41671421), Natural Science Foundation of China (41705056) and the Natural Science Foundation of Jiangsu Province (BK20170638). **Acknowledgments:** All the MODIS data (Land Cover product, AOD, EVI) were generated from MODIS LP DAAC archive. Temperature, scPDSI were obtained from CRU, and precipitaion from TRMM. Radiation used in this study was downloaded from CERES. GRACE RL05 mascon data were received from Center for Space Research at [[http://www2.csr.utexas.edu/grace/RL05_mascons](http://www2.csr.utexas.edu/grace/RL05_mascons)]([http://www2.csr.utexas.edu/grace/RL05_mascons](http://www2.csr.utexas.edu/grace/RL05_mascons)).