Fig. 1: Streamflow reconstruction and hydrological dynamics for the Negro River.

a Topography of the Negro River basin, including the locations of the hydrological station and sampling sites. The control basin for the hydrological station (Primera Angostura) is provided by the Global Runoff Data Center (GRDC)⁵². b Spatial correlation patterns between observed annual streamflow in the Negro River and runoff from the G-RUN dataset⁸³, considering the period from 1928 to 2017. The Negro River basin is highlighted and dots indicate the 95% significance level, same as below. c Schematic diagram of the large-scale spatial location and main circulations. The topographic base-map for (a) and (c) is sourced from Natural Earth. d A photograph of sampling sites for Araucaria araucana trees. e Reconstructed October–January streamflow in the Negro River during 1197–2023, after bias correction using Quantile Mapping (QM) method^54,55,56,57. An 11-year low-pass filtered curve was applied to highlight the low-frequency variability. The horizontal middle line presents the mean and the horizontal dashed lines represent the mean ±1.5 standard deviations (SDs). The gray shadow represents ± root mean square error (RMSE) while circles represent extreme years. Also provided simultaneously are the running 45-year slope and the decline severity (calculated by multiplying the mean slope by the duration; slopes must be below zero for more than 11 consecutive years)⁵⁹ for the reconstructed streamflow. The width of the bars indicates the start and end dates of each decline period.