Hydroclimatic influence of atmospheric rivers on vegetation and wildfire susceptibility across South America

This study investigates the role of atmospheric rivers (ARs) in modulating precipitation and wildfire activity across South America using the European Centre for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5) together with Moderate Resolution Imaging Spectroradiometer (MODIS) burned area, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) observations. The results reveal widespread declines in AR frequency and AR-associated precipitation across much of the continent, particularly during March–May (MAM) and June–August (JJA) over the Brazilian savanna (Cerrado) and Chaco, regions characterized by extensive burned area and recurrent wildfire activity. Spatial and temporal analyses reveal a dual role of ARs in regional fire dynamics. On short timescales (0–3 months), enhanced AR-associated precipitation suppresses fire activity by increasing fuel moisture and reducing incoming surface solar radiation through greater cloud cover. At longer lags (3–6 months), enhanced moisture availability promotes vegetation growth and fuel accumulation, producing dry biomass that can subsequently increase wildfire susceptibility during the following dry season. In central Brazil, burned area peaks and negative precipitation–fire correlations occur at lags of approximately 3–4 months, highlighting the delayed response of ecosystem productivity and fire occurrence to AR variability. Variations in AR activity are accompanied by large-scale circulation anomalies, including upper-level trough–ridge patterns and changes in Integrated Vapor Transport (IVT), which modulate regional moisture transport, precipitation, and the subsequent vegetation–fire response. These findings demonstrate that future changes in AR frequency and intensity may substantially influence the hydroclimate, vegetation productivity, and wildfire regimes of South America, with important implications for fire early-warning systems, ecosystem management, and climate adaptation strategies.