Caatinga is a typical biome of Brazil's semiarid regions and subject to climate changes. Research is needed on the relation of its features to climate events. This study analyzed the influence of rainfall and its irregularities in open and dense woody Caatinga vegetation. Phenological curves were generated by means of Normalized Differ-ence Vegetation Index (NDVI) time profiles in the Grota do Angico Conservation Unit study area in Sergipe State. Rainfall data from 2000 to 2018 were collected and phe-nological curves generated using various estimate methods that produced the following variables: [start of season, end of season, peak of season position, length of season, mean growing season and maximum seasonal]. Rainfall showed a standard intra-annual behavior, with inter-annual varia-tions related to irregularities influencing Caatinga response. Dense Caatinga vegetation had higher values of NDVI in all periods, even in anomalous years compared to open Caat-inga, in addition to having longer leaf coverage over the year, with an anticipated start and a more extended seasonal end. The analysis of the rainfall regime made it possible to assess its influence on the Caatinga and phenological profiles proved to be fundamental to understand periods of physi-ological change of open and dense Caatinga. These results indicate that dense Caatinga maintains physiological activ-ity longer, which may be associated with greater moisture maintenance in a semiarid region. In addition, because it has a greater leaf cover for longer periods, the soil may be preserved and maintain its characteristics longer, reducing the effects of desertification. The results may be associated with the type of forest management and conservation in this region. The total or partial suppression of individual rem-nants of Caatinga should be avoided, since the most open areas have lower photosynthetic capacity, affected to a con-siderable extent from the effects of adverse climatic condi-tions. Additionally, open Caatinga has a reduced capacity for regenerating naturally and its use by communities in this semiarid region should be limited.