# Adjustments to SIF Aid the Interpretation of Drought Responses at the Caatinga of Northeast Brazil
## 5 Conclusions  
In this study of the semiarid Caatinga vegetation of northeast Brazil, we attempted to characterize eleven years of Sun-induced chlorophyll fluorescence (SIF) seasonality (from 2007 to 2017) and SIF responses to a major drought in 2012. To achieve these objectives we adjusted SIF through combination with NDVI and also used angular adjustments to SIF provided with original GOME-2 data. Originaland modified SIF measures were tested against environmental data using time-series decomposition, rank correlation tests and linear mixed models (LMMs).  
Results demonstrated that seasonal variation and drought responses of adjusted SIF emissions at the community/landscape level correspond to previously reported leaf-level physiological responses. These observations are more relevant since they include both red and far-red SIF, as well as their ratio, and they were made in the complex and heterogeneously structured plant communities of the semiarid Caatinga of northeast Brazil. Our results with angular and spectral adjustments to SIF, although partially implemented with geometrically and radiometrically incompatible data (GOME-2 SIF and MODIS MAIAC SVIs), suggest that many of the assumptions behind the tested adjustments are likely correct. Our findings are relevant considering GOME-2 SIF's low spatial resolution and the noise inherent to measurements taken from this area due to the South Atlantic Anomaly. Here we show for the first time that environmental responses measured through adjusted GOME-2 SIF correlate with a known emergent ecosystem property (resilience), illustrating its value for ecological studies of vegetation.  
We suggest that more studies testing angular and spectral adjustments to SIF using higher definition SIF data in combination with other reflectance data are necessary to improve our understanding of landscape-level vegetation responses. Furthermore, continuous chlorophyll fluorescence measurements from tower-based instruments and coordinated field campaigns are recommended to increase our understanding of vegetation ecophysiological responses at different scales, to validate our findings and to allow predictions of possible ecological shifts resulting from the ongoing global climate change.  
Conceptualization, E.B. and F.P.; methodology, E.B.; software, E.B. and R.D.; formal analysis, E.B.; resources, F.P. and D.V.; data curation, E.B. and R.D.; writing--original draft preparation, E.B.; writing--review and editing, E.B., R.D., F.P. and D.V.; supervision, F.P. and D.V.; funding acquisition, E.B., R.D., F.P. and D.V. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the PCI program of CNPq, the Brazilian National Council of Research, grant number 313142/2016-5, and by the Sao Paulo Research Foundation (FAPESP), grant 2015/22987-7 and by the Foundation for Science and Application of Space Technology (FUNC).  
The authors thank [PERSON] for his comments and suggestions on this manuscript, [PERSON] for his instrumental advice on time-series analysis, NASA for the freely available data, [PERSON] and his team for the MODIS-MAIAC corrections, [PERSON] for the helpful discussion and the Foundation for Science and Application of Space Technology (FUNC) for its support.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.