Reclamation Information Sharing Environment (RISE)

Flood-risk context for the Missouri River basin is extended through the development of tree-ring based annual streamflow reconstructions. Water-year flows at Hermann, Missouri were reconstructed for 1360–1900 by combining modeled natural streamflow for 1901–2020 and tree-ring chronologies beginning in 1360. Two complementary statistical methods—non-parametric K-nearest neighbor resampling and principal component regression—were applied, and highly consistent multi-century flow estimates were produced. Wavelet analysis was used to guide the identification of potential flood years, which were determined from percentile-flow thresholds evaluated within 16-, 32-, and 64-year moving windows. Across 1360–2020, 172 potential flood years were detected, with 126 occurring in both reconstructions, indicating strong agreement between the methods. Event frequency was found to increase from the late eighteenth to mid-nineteenth century and to remain relatively stable after approximately 1850, providing historical context for recent severe floods (e.g., 1993, 2011, 2019). Through this wavelet-informed approach, potential flood years—rather than flood magnitudes—were identified, and this novel methodology was structured so it may be applied broadly across other river basins. The resulting multi-century record offers long-term context that can be used to support flood-risk assessments and operations studies, while also establishing a foundation for subsequent development of seasonal reconstructions and duration-based metrics to enhance flood frequency analysis.