Long-term snow variability from tree-rings in the British Columbia Pacific Ranges

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Ongoing and accelerating hydroclimatic changes in the Coast Mountains are having lasting ecological, economic and social consequences. These changes are noteworthy in the Pacific Ranges, where the annual peak snow water equivalent (SWE) is the primary driver of seasonal water supply availability. While little is known about the spatial or temporal characteristics of SWE within much of this area, recent snowpack declines have led to reduced streamflow in many watersheds. Historical SWE and runoff records are sparse and of short duration in this region, making it difficult to determine whether similar low snow events have occurred in the past, or whether recent streamflow droughts are unprecedented. The proposed research is intended as a multi-scale tree-ring study that would enable a broad spatial and temporal understanding of snow dynamics within the Pacific Ranges. Significant contributions to climate science have firmly established tree-rings as invaluable sources of proxy data for describing hydroclimate variability, and as useful tools for evaluating hydroclimate history on decadal to millennia timescales in regions with few or limited-duration records. The research will detail the climate response of forest stands where deep snowpacks negatively limit the growth of mountain hemlock trees and positively influence the growth of Douglas-fir trees. Over 100 stands will be sampled, with ring width, earlywood and latewood density, and blue intensity chronologies constructed following standard protocols. Once the snow sensitivity of the chronologies is established, relevant predictors will be used to construct proxy snow records spanning the duration of the chronologies. To broaden and regionalize the reconstructions, ClimateWNA will be used in conjunction with the chronologies to provide site-specific snow histories, with time series and cluster analysis, as well as spatial statistics used to evaluate long-term spatial and temporal trends. Overall, the research will provide important insights into the representativeness of historical SWE datasets, as well as allow for an innovative understanding of multi-century trends, variability and teleconnection relationships. It is expected the chronologies will generate new information on natural SWE and snow variability on annual to millennial timescales, thereby providing the insights crucial for describing the causal factors behind the low-frequency regime shifts that lead to spatially and temporally synchronous hydroclimatic events. The findings provide the insights needed to understand the compounding impact of decadal variability and anthropogenic warming on recent changes to SWE-generated runoff in this setting, information sought after by all those charged with managing the impact of declining snowpacks on community water-supplies, hydroelectric power generation and local Pacific Salmon populations.**