Networks of Tree-Ring Based Streamflow Reconstructions for the Pacific Northwest, USA

Water resources in the Pacific Northwest (PNW) are characterized by significant interannual to interdecadal variation. Paleo-proxy reconstructions such as those derived from tree-rings provide longer-term context and supplement information on this expected range of variability, which can improve planning, management, and response related to extreme events and hydrologic change. However, existing paleo-proxy reconstructions have yet to address the potential for pronounced within- and among-basin variations in the PNW due to a lack of spatial coverage. Here we develop methodologically consistent reconstructions for 36 gages in the PNW, including the Columbia and Snake River drainages, as well as key coastal watersheds. These reconstructions extend back at least to the 1500s coefficient of efficiency. Reconstruction skill is relatively high (mean R-2 = 0.63), and snowpack- or winter precipitation-sensitive chronologies from high-elevation sites provide important contributions to reconstruction skill. At the whole-region scale, reconstructed variability indicates evidence for drier and wetter years, more persistent decadal variability, and correspondingly longer episodes of deficit and surplus compared to instrumental records. Within the region, this expanded range of extremes appears especially prevalent in the Snake River and southern PNW watersheds. Regionally, cumulative deficits in the early 1500s and mid 1600s rival those of the early 20(th) century, though persistence and timing vary widely among basins. These reconstructions suggest that considering within-region variability will be key for water management and planning under climate change, and that sub-regional adaptation strategies are likely to be advantageous.