Reconstructing the Hydroclimatic History of the Mississippi River Basin Over the Past Millennium

The Mississippi River Basin (MRB) is the largest watershed in the United States and plays a central role in regional hydroclimate. This study reconstructs annual streamflow variability in the MRB from the year 1200 to 2005 by applying principal component regression to streamflow data from 51 gauges and the North American Drought Atlas (NADA), a tree‐ring‐based reconstruction of the summer Palmer Drought Severity Index (PDSI). By reconstructing basin‐wide streamflow variability over the last 800 years, this study provides a multi‐centennial framework for evaluating the persistence, spatial coherence, and full distribution of hydroclimate variability in the MRB. Verification statistics against the observed record, including the Coefficient of Efficiency, CE, measuring reconstruction skill relative to the mean, Calibration R 2 , CRSQ, indicating variance explained during calibration, and Validation Reduction of Error, VRE, assessing predictive skill on withheld data, demonstrate strong predictive performance across the entire MRB. Basinwide streamflow variability is closely tied to remote large‐scale climate patterns, and the reconstruction captures the three leading modes of hydroclimatic variability in the MRB. The extended streamflow record offers critical insights into the long‐term hydroclimate variability in the MRB, spanning interannual to centennial timescales, and can be directly leveraged to enhance water resource management and better constrain future climate change projections.