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Dendrohydrological Reconstruction of North Fork Nooksack River August Streamflow from Subannual Mountain Hemlock Ring-Widths
Date of Award
Department or Program Affiliation
Master of Arts (MA)
Bunn, Andrew Godard
Mitchell, Robert J. (Geologist)
Climate warming is driving changes to snowpack and streamflows in snow and ice-driven systems throughout the world. To better understand present and future conditions, we need to examine conditions prior to the onset of climate warming. Tree ring records are used widely to reconstruct pre-instrumental climate and hydrological records. Some locations are more conducive to this methodology than others, however, and moisture-rich environments such as the west slopes of the Cascade mountains continue to present challenges to effective hydrological record reconstruction. Previous researchers working in this environment have employed several techniques in response to this problem, which require integrated dendrochronological and hydrological modeling, independently reconstructed climate records, or access to an X-ray densiometer. We advocate for the use of a less costly technique in terms of skill, data, and money that can be used alone or in tandem with more advanced techniques to improve the quality of hydrological reconstruction models in this environment: subannual ring-width measurements. As of yet, no one has applied this technique to the species mountain hemlock (Tsuga mertensiana), or to streamflow reconstruction modeling in the coastal Pacific Northwest. We found that separating annual ring-widths into subannual earlywood and adjusted latewood measurements resulted in stronger and less confounded associations with climate and hydrological data, and significantly improved the skill of a streamflow reconstruction model of average August streamflow of the upper North Fork Nooksack River in northern Washington State, USA. Earlywood associated most strongly with winter through summer snowpack of the same water year, and adjusted latewood associated most strongly with late summer temperature and precipitation of the same and previous water year. Earlywood contained a streamflow signal from the same water year and adjusted latewood contained a streamflow signal from the previous v water year, allowing for the development of a streamflow reconstruction model. We observed an improvement in reconstruction model fit of 7% using earlywood and forward-lagged adjusted latewood rather than annual ring-width.
dendrochronology, dendrohydrology, hydroclimate, cascades, subannual, earlywood, latewood, tree rings, mountain hemlock, streamflow, discharge, reconstruction, Nooksack River
Western Washington University
Subject – LCSH
Dendrochronology--Washington (State)--Nooksack River; Tree-rings; Mountain hemlock--Cascade Range; Streamflow--Washington (State)--Nooksack River; Climatic changes--Washington (State)--Nooksack River
Nooksack River (Wash.); Cascade Range
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LaGassey, Hannah, "Dendrohydrological Reconstruction of North Fork Nooksack River August Streamflow from Subannual Mountain Hemlock Ring-Widths, Cascade Mountains, Washington State" (2023). WWU Graduate School Collection. 1209.