Impacts of Fire on Flow Magnitude and Variability in the Southeastern Amazon Basin

Abstract Increasing fire within the Amazon rainforest is a significant disturbance that has the potential to alter flow regimes and subsequently impact local ecology and ecosystem services. While previous studies have examined the impact of land cover change on streamflow, the specific effects of fire on the hydrology of Amazonian forested catchments remain uncertain, especially in previously undisturbed forests. This study investigates the impacts of fire on hydrology in the Amazon using a before‐after control‐impact (BACI) paired‐watershed approach. Our analysis tested for post‐fire changes in the magnitude and variability of the streamflow regimes of five watersheds in the southeastern Brazilian Amazon. Flow regime magnitude and variability were quantified using monthly basin yield and coefficient of variation, number of reversals, and average rise rate. Differences in metrics before and after fire disturbance were assessed relative to nearby reference watersheds. Following fire disturbance, three of five watersheds showed increases in magnitude and four watersheds showed increases in variability. Fire effect size ranged from 6.01% to 7.98% for streamflow magnitude and from 10.9% to 70.3% for variability. Our findings confirm that fire affects streamflow in the Amazon, with the primary impacts being increases in streamflow variability. Overall, this study provides insights into the impact of fire on Amazonian catchment hydrology and highlights the importance of considering fire as a factor in managing and protecting tropical forest ecosystems.