A multi-century Sierra Nevada snowpack reconstruction modeled using upper-elevation coniferous tree rings (California, USA)

Snowpack in the Sierra Nevada Mountains accounts for around one-third of California's water supply. Melting snow provides water into dry summer months characteristic of the region's Mediterranean climate. As climate changes, understanding patterns of snowpack, snowmelt, and biological response is critical in this region of agricultural, recreational, and ecological value. Here we investigated the relationships between tree rings of montane conifer trees (Tsuga mertensiana, Abies magnifica, Abies concolor, Calocedrus decurrens, Juniperus occidentalis, and Pinus ponderosa) and regional climate indices with the goal of reconstructing April 1 snow-water equivalent (SWE) in the North Fork American River watershed of the Sierra Nevada. Chronologies were positively correlated with April 1 SWE of the year prior to ring formation. Temporal trends in correlation between tree-ring chronologies and climate indices indicate strengthening tree growth response to climate over time. We developed a skillful, nested reconstruction for April 1 SWE, 1661-2013. Variability of the reconstruction is within the envelope of 20th and 21st-century variability; however, the 2015 record low snowpack is unprecedented in the tree-ring record, as in results from previous studies. Future research should focus on integrating modern snow sensor data into paleoclimate research and understanding mechanistic linkages between snow and tree growth response.