Degradation amplifies Amazon forest vulnerability to extreme drought: evidence from the 2023–2024 ENSO event

The Amazon rainforest is a cornerstone of global climate regulation, carbon sequestration, and biodiversity conservation. However, its resilience is increasingly undermined by the combined pressures of mega-scale recurrent ENSO droughts and forest degradation. Such mega-droughts, amplified by rising temperatures and declining water, are known to suppress tropical forest functioning. Yet the basin-wide sensitivity of degraded versus intact forests to these events has remained poorly quantified. Here, we present preliminary basin-scale analyses of the unprecedented 2023–2024 Amazon drought, which was driven by a confluence of large-scale climatic anomalies, including a strong El Niño, tropical North Atlantic warming, and widespread marine heatwaves. This drought event produced record-low rainfall, sustained soil moisture deficits, and temperature anomalies across much of the basin. Leveraging satellite-derived canopy greenness (Enhanced Vegetation Index, EVI) and spatially paired comparisons between degraded and intact forest areas, we find that degradation markedly amplifies drought impacts: degraded forests exhibited an average greenness loss 2.43 times greater than intact forest during this drought event. Machine-learning attribution highlights drought duration and soil fertility as the dominant drivers of this vulnerability gap, with secondary modulation by baseline climatic conditions and canopy height loss. Predictive simulations further indicate that even moderate future degradation of currently intact forests could trigger functional impairment under recurring drought regimes, with northern white-sand zones and southern Arc of Deforestation emerging as high-risk hotspots. These preliminary results provide the basin-wide evidence that forest degradation and extreme drought act synergistically to intensify vegetation greenness decline, reframing Amazonian resilience as conditionally stable and highly sensitive to forest degradation. This work underscores the urgent need to incorporate forest degradation into climate impact assessments and conservation strategies to safeguard the Amazon’s ecological and climate-regulating functions.