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 the Truckee-Carson River Basin (California/Nevada watersheds with headwaters in the Sierra Nevada) and similar basins in semi-arid environments 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 conifer species (Abies magnifica, Juniperus occidentalis, Pinus ponderosa, Pinus jeffreyi, Tsuga mertensiana) in the Sierra Nevada were used to develop a series of standardized reconstructions of water-year regional precipitation using stepwise linear regression on lagged chronologies. A nonparametric analysis approach was then used to classify positive and negative whiplash events in observed and reconstructed regional precipitation. The statistical significance of matching events in regional precipitation by tree-ring reconstructions was assessed using a hypergeometric test. Results suggest that reconstructions from individual species and single sites of those species are often able to track whiplash events. Negative events (wet to dry) are generally tracked more consistently than positive events (dry to wet), although tracking sensitivity differs among species and especially strong tracking of positive events is exhibited by Tsuga. Tracking ability does not exhibit a linear relationship with the explained variance of a reconstruction and has little apparent relationship to the magnitude of whiplash events or the monthly distribution of annual precipitation during those whiplash years.