The Response of Vegetation Productivity to the El Niño-Southern Oscillation in Southeast Asia

The El Niño-Southern Oscillation (ENSO) is a large-scale global climate pattern that significantly influences tropical vegetation productivity. However, the responses of vegetation productivity in Southeast Asia (SEA) to different ENSO phases remain unclear. In this study, we used multisource gross primary productivity (GPP) products and explainable machine learning method (SHAP) to assess the status of ENSO phases during 1981–2019 and their impact on vegetation productivity in SEA. Our results reveal that El Niño and La Niña have exhibited opposite trends over the past 40 years, with El Niño events decreasing in both frequency and intensity, while La Niña events have become more frequent since the 21st century. Precipitation and radiation showed distinct and opposing variation patterns across different ENSO phases, whereas temperature variations exhibited a regional pattern that differed from global trends. The average temperatures during both El Niño and La Niña were slightly lower than during the neutral phase. ENSO-induced climate anomalies affected vegetation productivity, resulting in a decrease in GPP of 72.3 ± 48.1 gC m⁻² yr⁻¹ during El Niño and an increase of 31.0 ± 44.4 gC m⁻² yr⁻¹ during La Niña. Based on SHAP analysis, we found that soil moisture was the primary driver of GPP during ENSO events, with a distinct threshold effect that dynamically shifted with water availability. Furthermore, terrestrial water storage (TWS) predominantly drove variations in atmospheric CO₂ growth rate during the land-atmosphere carbon exchange process, with its influence intensifying over time. This study highlights the critical importance of water stress in regulating the carbon cycle of tropical vegetation in SEA.