Influence of climate variability on leaf phenology in seasonally dry tropical ecosystems

Drought is regarded as one of the most significant consequences of climate change for ecosystem dynamics. In tropical dry ecosystems, where seasonal drought is a key climatic feature, intensified dry conditions can significantly disrupt vegetation responses, particularly leaf phenology, which directly regulates carbon uptake, water exchange, and ecosystem productivity. Despite this, the extent to which climate variability and drought events drive long-term phenological responses remains insufficiently understood, especially in seasonally dry tropical forests (SDTFs).  In this study, we investigated how climate variability and drought severity influence leaf phenology in two major SDTFs: the Caatinga and the Cerrado. Drought severity was assessed using the Standardized Precipitation Evapotranspiration Index (SPEI) across three long-term monitoring sites: Caatinga (CAAT) and Cerrado (CORE and PEG). To capture ecosystem-scale phenological dynamics, we analyzed long-term (2000–2023) satellite-derived phenological time series based on the Enhanced Vegetation Index (EVI), and assessed drought impacts through phenocamera observations focused on individual tree crowns at each site. Our results show that all study sites experienced moderate to exceptional droughts during the study period, with prolonged dry conditions frequently coinciding with marked vegetation anomalies detected by EVI, particularly in the Caatinga, reflecting prolonged periods of reduced canopy cover during the dry season. Interannual variability in the start of the growing season (SOS) was influenced by climatic drivers, with rainfall generally promoting earlier leaf flushing in the Caatinga, while drier years were associated with delayed SOS. In the Cerrado, higher temperatures appeared to interact with delayed SOS patterns. These findings highlight contrasting climatic controls on leaf phenology across ecosystems and reinforce the role of climate variability in shaping phenological dynamics in tropical dry biomes under extreme events.

Keywords: Caatinga, extreme events, Leaf phenology, climate variability

Acknowlegments: The authors gratefully acknowledge the financial support from the São Paulo Research Foundation (FAPESP) Grants (#2021/10639-5, #2022/02323-0, #2022/07735-5) and felowships #2024/06113-6, #2023/05323-4 and 2025/19074-1, the Pernambuco State Research Support Foundation (FACEPE) (Grant # BFP-0103-5.01/23), the National Council for Scientific and Technological Development (CNPq) Grants #403692/2024-5 and #306562/2022-3 (Productivity fellowship to PM), the Coordination for the Improvement of Higher Education Personnel-CAPES (Finance code 001), and the Brazilian Agricultural Research Corporation (EMBRAPA) (Grants #10.23.00.111.00.00 and 10.25.00.144.00.00).