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New Columbia River streamflow reconstruction


A study funded in part by CPO’s Sectoral Applications Research Program developed an improved  reconstruction of the Columbia River streamflow using tree-ring records sensitive to climate forcings. The study appears in the Journal of the American Water Resources Association.
This study incorporated major seasonal controls of hydrologic variability and updated regional tree-ring records, as well as new tree-ring chronologies that take into account water-limited and snowpack-limited chronologies to reconstruct streamflow at The Dalles, Oregon. These reconstructions were then compared to other existing hydroclimatic reconstructions, as well as global climate and hydrologic models, to assess potential future impacts to water resources in the Columbia River Basin.
Past research points to severe droughts for the Columbia River Basin, although few reconstructions in western United States have included snowpack-limited tree-ring chronologies. Understanding the possible changes in streamflow of the Columbia River is essential for future water resources strategies, given the Columbia River Basin’s importance to the economy and livelihood of the Pacific Northwest.

We developed Columbia River streamflow reconstructions using a network of existing, new, and updated tree-ring records sensitive to the main climatic factors governing discharge. Reconstruction quality is enhanced by incorporating tree-ring chronologies where high snowpack limits growth, which better represent the contribution of cool-season precipitation to flow than chronologies from trees positively sensitive to hydroclimate alone. The best performing reconstruction (back to 1609 CE) explains 59% of the historical variability and the longest reconstruction (back to 1502 CE) explains 52% of the variability. Droughts similar to the high-intensity, long-duration low flows observed during the 1920s and 1940s are rare, but occurred in the early 1500s and 1630s-1640s. The lowest Columbia flow events appear to be reflected in chronologies both positively and negatively related to streamflow, implying low snowpack and possibly low warm-season precipitation. High flows of magnitudes observed in the instrumental record appear to have been relatively common, and high flows from the 1680s to 1740s exceeded the magnitude and duration of observed wet periods in the late-19th and 20th Century. Comparisons between the Columbia River reconstructions and future projections of streamflow derived from global climate and hydrologic models show the potential for increased hydrologic variability, which could present challenges for managing water in the face of competing demands.

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