Atmospheric moisture transport anomalies and vegetation response in arid coastal ecosystems: insights from the 2017 coastal El Niño in northern Peru

Introduction: Atmospheric moisture transport governs oceanic evaporation with terrestrial water availability. However, its role in regulating vegetation activity in arid coastal ecosystems is still poorly understood. In particular, how transient circulation anomalies, such as coastal El Niño events, modify atmospheric moisture conditions and relate to vegetation dynamics at broader spatial scales has received limited attention. Methods: This study combines an event-based analysis of atmospheric moisture transport during the 2017 coastal El Niño in northern Peru with a global statistical analysis of vegetation-moisture relationships. Low-level moisture transport pathways and moisture properties were examined using backward trajectory analysis. Vegetation activity was represented by leaf area index. Spatial correlations between leaf area index and water vapor transport were evaluated within coastal buffer zones and across global land grid cells. Results: The 2017 coastal El Niño was associated with a clear reorganization of low-level moisture transport pathways, with four dominant trajectory clusters identified compared to three in 2009. The largest equatorial Pacific pathway accounted for approximately 60% of trajectories in 2017, whereas two southeastern Pacific clusters represented nearly 90% of trajectories under normal conditions. Air parcels reaching the Peruvian coast contained substantial higher moisture content, with specific humidity frequently exceeding 15 g/kg compared to generally below 10 g/kg in 2009. This indicates significantly altered near-surface atmospheric conditions. At the global scale, relationships between leaf area index and water vapor transport varied strongly across regions. Positive associations were mainly observed in moisture-limited regions, particularly across large parts of the Southern Hemisphere and several arid coastal zones. In contrast, negative or weak associations dominated humid tropical regions and much of the Northern Hemisphere. Discussion: These results indicate that atmospheric moisture transport influences vegetation activity in a region-dependent manner. Its role is more pronounced in arid and moisture-limited environments than in humid regions. By linking an event-scale moisture transport anomaly with global vegetation-moisture relationships, this study provides insight into vegetation sensitivity to circulation-driven moisture variability, particularly in arid coastal ecosystems.