Species Sensitivity to Hydrologic Whiplash in The Tree-Ring Record of
the High Sierra Nevada
Abstract
Year-to-year variability of precipitation and temperature has
significant consequences for water management decision making.
“Whiplash” is a term which describes this variability at its most
severe, referring to events at various timescales in which the
hydroclimate switches between extremes. Tree-rings in semi-arid
environments like the Truckee-Carson River Basin (California/Nevada
watersheds with headwaters in the Sierra Nevada) can provide proxy
records of hydroclimate as their annual growth is tied directly to
limitations in water-year rainfall and temperature, but traditional
metrics of reporting explained variance do not distinguish a
reconstruction’s sensitivity to whiplash events. In this study, a pool
of total ring width indices from five snow-adapted conifer species
(Abies magnifica, Juniperus occidentalis, Pinus ponderosa, Pinus
jeffreyi, Tsuga mertensiana) were used to develop a series of
standardized reconstructions of water-year PRISM precipitation (P12)
using stepwise linear regression. A nonparametric analysis approach was
then used to determine positive and negative whiplash events in
reconstructed and instrumental precipitation records. Hypergeometric
distribution of the resulting timeseries datasets illustrates
relationships between reconstructions and recorded whiplash events and
allows for determination of patterns in tree-ring growth response. The
results of this study suggest that ring-width indices from the assessed
conifer species in the snow-belt of the Sierra Nevada are often able to
record consecutive years of opposing extreme precipitation and report
such events through derived models. Negative WL events are tracked more
consistently across species in site-specific reconstructions of P12 than
positive ones. It appears that residual effects of a preceding year’s
drought or pluvial do not necessarily suppress records of WL, though
sensitivity to precursor conditions in tracking of WL events may differ
across species, and the absolute WL events captured in a reconstruction
vary.