## 5 Conclusions  
In summary, the SITE model satisfactorily reproduced the seasonal variability of both energy and carbon balance. This is a pioneering study on the analysis of CO\({}_{2}\) exchange under conditions of extreme drought (2012 with 198.2 mm) and heavy rainfall (2009 with 1019.6 mm) in relation to the climatology (758.0 mm). It reveals the impacts of contrasting precipitation years on the intra- and interannual variability of energy fluxes and CO\({}_{2}\) fluxes in the Caatinga biome. In general, the results showed the relationship between rainfall seasonality, energy balance partitioning, and the dynamics of the CO\({}_{2}\) balance in the Caatinga. The annual mean GPP varied from 7.52 umol m\({}^{-2}\) s\({}^{-1}\) in 2009 to 4.62 umol m\({}^{-2}\) s\({}^{-1}\) in 2012, and the NEE was 57% higher in the wettest year (2009) compared to the extremely dry year (2012) due to surface water scarcity. H and LE exhibited significant differences between the studied years, even during the dry and wet seasons, with H consistently higher regardless of the time of year. Even in the year with above-average rainfall, H remained higher than LE. However, this predominance is likely associated with the tendency of the SITE model to underestimate fluxes, mainly due to the model's limitation in capturing LE peaks during periods of extreme drought. On the other hand, net radiation showed seasonality linked to variations in solar radiation, which was similar in the years 2009 and 2012. The direct influence of rainfall on CO\({}_{2}\) exchanges is shown through the strong relation (R\({}^{2}\) > 0.48) observed in the regression analyses between GPP, NEE, NEP, and rainfall. The monthly values of the CO\({}_{2}\) balance components exhibit an asymptotic relationship with rainfall during the wet season, stabilizing after a monthly rainfall threshold of 300 mm. GPP, NEE, and Reco are directly influenced by the occurrence of rainfall in the Caatinga biome. In the year with high rainfall values (2009), the release of CO\({}_{2}\) to the atmosphere was reduced. On the other hand, in the year with low rainfall values (2012), the peaks of carbon uptake were lower, but this was offset by a reduction in Reco. Nevertheless, the Caatinga biome continued to act as a sink for CO\({}_{2}\) even during the year of extreme drought. Given the importance of terrestrial carbon sinks to the global climate, attention is needed to create and strengthen policies to mitigate greenhouse gas emissions and to restore and protect seasonally dry tropical forests. Conceptualization, K.R.M., A.M.S.M., C.M.S.e.S. and B.G.B. ; methodology, K.R.M., A.M.S.M., B.G.B. and C.M.S.e.S. ; validation, K.R.M., A.M.S.M., C.M.S.e.S., B.G.B., P.R.M., P.E.S.O., D.T.R., G.B.C., R.R.F., A.C.N.d.S., L.F.M., J.R.S.L., A.C.D.A. and R.S.C.M. ; formal analysis, K.R.M., A.M.S.M., C.M.S.e.S., B.G.B., P.R.M., P.E.S.O., D.T.R. and G.B.C. ; writing--original draft preparation, K.R.M., A.M.S.M. and B.G.B. ; writing--review and editing, K.R.M., A.M.S.M., C.M.S.e.S., B.G.B., P.R.M., P.E.S.O., D.T.R. and G.B.C. ; visualization, K.R.M., A.M.S.M., C.M.S.e.S., B.G.B., P.R.M., P.E.S.O., D.T.R., G.B.C., R.R.F., A.C.N.d.S., L.F.M., J.R.S.L., A.C.D.A. and R.S.C.M. All authors have read and agreed to the published version of the manuscript. This research was funded by National Council for Scientific and Technological Development (CNPq) grant number 420854/2018-5 and for the productivity grant conceded to the authors [PERSON] and [PERSON]. (grant n\({}^{\circ}\) 310781/2020-5 and 314257/2021-7, respectively), and to FUNPEC/UFRN for financial support (Project n\({}^{\circ}\) 372022). To National Council for Scientific and Technological Development (CNPq) for the research productivity grant of the author [PERSON]. (Process n\({}^{\circ}\) 303802/2017-0) and the financial support in the NOWCDCB project: National Observatory of Water and Carbon Dynamics in the Caatinga Biome (INCT-MCTI/CNPq/CAPES/FAPs 16/2014, grant: 465764/2014-2 and MCTI/CNPq N\({}^{\circ}\) 28/2018, grant 420854/2018-5).