This project aims to provide high-quality, long-term records of past streamflow in the Lower Missouri River (LMR) basin by integrating select gage records, modeled hydrology, and several complementary dendrochronology reconstruction approaches focusing on water-year and seasonal generation of runoff and the improved capture of extremes. This project seeks to: (1) incorporate gage data, estimates of natural flow, and modeled hydrology to develop streamflow calibration series; (2) generate reconstructions of streamflow for key sub-basin gages in the LMR, along with spatial reconstructions of runoff for the basin; (3) evaluate multi-century synoptic climate controls on LMR flow within a broader North American context; and (4) analyze the impact of warming temperatures on future flow patterns. Extreme events (floods and droughts) have been common in the LMR over the past several decades, but the context for understanding the long-term hydroclimate variability impacting flow is limited due to a paucity of long streamflow records that are unaffected by human modification. The LMR basin is one of the few remaining major river systems in the U.S. lacking streamflow reconstructions in large part due to the scarcity of reliable instrumental data for flow calibration The potential Broader Impacts (B.I.) include an improved baseline understanding of droughts/floods/pluvials in the Lower Missouri River Basin and the involvement of stakeholders at all levels including water resource managers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.