**5. Conclusions**

This study observed that using the EVI time series efficiently estimated phenological parameters. The determination of the phenological parameters for 20 years allowed the evaluation of their seasonality. The seasonality of Caatinga vegetation growth differed between the three experimental sites. The SOS was the parameter that presented the greatest variability in the days of the year (DOY), reaching a variation of 117 days. The high variability of SOS occurred in sites with low variability of EOS and vice versa. The relationship between air temperature and vegetation was insignificant for the two experimental sites and presented a significant value for the site drier (MSD). At the experimental site where the highest vegetative peak co-occurred with the low air temperature, the highest LOS and AMPL were observed. In addition, the values of LOS and AMPL are directly

linked to the annual distribution of rainfall, and the longer the rainy season, the greater their values are. The variability of the natural cycles of the environmental drivers that regulate the ecosystem's phenology and the influence on the Caatinga's natural dynamics indicated a greater sensitivity of the vegetation to water availability, with the water deficit being the limiting factor of the vegetation. There is a greater need for new research and studies aiming to reduce the impact of climatic risks by characterising and quantifying species' response patterns to likely climate change. There will be changes in phenological patterns, production, and spatial distribution. Quantifying these impacts and devising appropriate actions to minimise such adversities represent significant research challenges in the coming decades.

**Author Contributions:** Formal analysis, R.M., J.A., M.M., A.M.P.-M. and C.A.C.d.S.; Investigation, R.M., J.A., M.M. and B.B.d.S.; Methodology, D.R. and J.C.; Software, R.M., J.A. and D.R.; Supervision, J.C.; Visualization, A.M.P.-M., C.A.C.d.S. and B.B.d.S.; Writing—original draft, R.M., J.A., D.R. and B.B.d.S.; Writing—review & editing, D.R., M.M., C.A.C.d.S. and J.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was financed by the Pró-Reitoria de Pós-Graduação e Pesquisa of the Federal University of Campina Grande (PRPG-UFCG).

**Acknowledgments:** The authors thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brazil (CAPES)-Finance Code 001 for the as a Brazilian CAPES scholarship to the first and second author, the project Nova geração de modelos para estimativas de evapotranspiração para o Semiárido Brasileiro (CNPq Proc. 409341/2021-5). This work forms part of the project Evolução na representação do balanço de energia por meio da integração de dados de campo e satélite aplicados a computação em nuvem para o semiárido brasileiro (FAPESQ under startup gran<sup>t</sup> number #010/2021). The authors are also grateful to CNPq for the PQ (Productivity and Research) grants to the sixth autor (Proc. 304493/2019-8).

**Conflicts of Interest:** The authors declare no conflict of interest.
