Gregory T. Pederson Connie A. Woodhouse Edward R Cook Gregory J. McCabe Erika K. Wise Patrick Erger Larry Dolan Marketa McGuire Subhrendu Gangopadhyay Katherine J. Chase Jeremy S. Littell Stephen T. Gray Scott St. George Jonathan M. Friedman David J. Sauchyn Jannine St. Jacques John W. King Justin T. Martin 2019 Paleohydrologic records can provide unique, long-term perspectives on streamflow variability and hydroclimate for use in water resource planning. Such long-term records can also play a key role in placing both present day events and projected future conditions into a broader context than that offered by instrumental observations. However, relative to other major river basins across the western United States, a paucity of streamflow reconstructions has to date prevented the full application of such paleohydrologic information in the Upper Missouri River Basin. Here we utilize a set of naturalized streamflow records for the Upper Missouri and an expanded network of tree-ring records to reconstruct streamflow at thirty-one gaging locations across the major headwaters of the basin. The reconstructions explain an average of 68% of the variability in the observed streamflow records and extend available records of streamflow back to 886 CE on average. Basin-wide analyses suggest unprecedented hydroclimatic variability over the region during the Medieval period, similar to that observed in the Upper Colorado River Basin, and show considerable synchrony of persistent wet-dry phasing with the Colorado River over the last 1200 years. Streamflow estimates in individual sub-basins of the Upper Missouri demonstrate increased spatial variability in discharge during the Little Ice Age (~1400-1850 CE) compared with the Medieval Climate Anomaly (~800-1400 CE). The network of streamflow reconstructions presented here fills a major geographical void in paleohydrologic understanding and now allows for a long-term assessment of hydrological variability over the majority of the western U.S. application/pdf 10.1016/j.quascirev.2019.105971 en Elsevier 1200 years of Upper Missouri River streamflow reconstructed from tree rings article