Sierra San Pedro Mártir, Baja California, cool‐season precipitation reconstructed from earlywood width ofAbies concolortree rings

Abstract

Tree ring data are analyzed for a multicentury record of drought history in the Sierra San Pedro Mártir (SSPM) of Baja California, Mexico. Climatic variation in the study area is of particular interest because the SSPM is a rich biotic environment at the southern limit of the California floristic province and the southern limit of the planetary jet stream. Future shifts in the jet stream would be expected to have amplified effect on this marginal environment. The study applies linear regression to tree ring indices of earlywood‐width ofAbies concolorto estimate a 353 year (1658–2010 C.E.) record of cool‐season (October–April) precipitation,P, in SSPM. Time‐nested regression models account for more than half the variance of grid pointPin calibration periods of length 50–65 years. Cross‐spectral analysis indicates strong tracking of observedPby the reconstruction over a broad range of frequencies. Robustness of the reconstruction is supported by synchrony of reconstructedPwith tree ring variations in other tree species from SSPM. The reconstruction emphasizes the severity of the 1950s drought in a long‐term context and the single‐year intensity of droughts in the last decade: 2007 stands out as the driest reconstructed year, with a high percentage of missing rings inA. concolor. The reconstruction identifies the early twentieth century pluvial as the wettest epoch in the last 353 years in the SSPM. High‐elevation tree species in SSPM may be especially well‐suited to sensing snowpack‐related moisture variations associated with a southerly branched jet stream and the types of weather systems active in the pluvial.