Characterizing long-term meteorological and flux variability of an old-growth tropical forest in the Central Amazon: a decade of ATTO tower observations

The Amazon Rainforest plays a key role in the Earth system, yet long-term continuous observations remain scarce. We analyzed more than a decade of continuous measurements (2013–2024) from the Amazon Tall Tower Observatory (ATTO) in central Amazonia, including separate analyses of extreme El Niño–Southern Oscillation (ENSO) warm phases (2015–2016 and 2023–2024). The results revealed seasonal contrasts: air temperature (T) and soil temperature (TS) showed little variation between seasons, whereas sensible heat flux (H), vapor pressure deficit (VPD), and photosynthetically active radiation (PAR) were higher in the dry season (July–November). In contrast, the wet season (January–May) was characterized by increased rainfall, relative humidity (RH), and soil moisture (θS). Latent heat flux (LE) dominated the partitioning of surface energy throughout the year, supported by θS, which increased with depth and responded to rainfall with a delay of approximately one month. This sustained forest functioning during the dry season despite high VPD. The CO2 flux remained negative throughout the year, although its magnitude decreased during the dry season. During the 2015–2016 and 2023–2024 El Niño events, T and VPD were anomalously high, while RH decreased, particularly in the dry season. Rainfall patterns also changed, with 2015–2016 below the long-term average mainly during the dry season of 2015 and at the beginning of the wet season in 2016, and 2023–2024 values remained below average during the 2024 wet season. The reduction in precipitation in 2014–2015 led to a decrease in carbon uptake during that period, which was not observed in 2023–2024. Radiation and energy fluxes were consistent with 2013–2024 averages, except for increased H and upward longwave radiation in the 2023 dry season. These results provide a reference for meteorological, energy, and carbon flux variability in the central Amazon and highlight the sensitivity of the region to large-scale climate drivers such as El Niño.