Published in T.R. Karl (ed.), 1999, Proceedings of the 10 th Symposium on Global Change Studies, American Meteorological Society, Boston, MA, pp. 303-306. 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N -0.2 -0.2 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.4 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 0 400 800 km Fig. 1. Correlation map between PDO and tree-ring chronologies of western North America. 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 130˚W 125˚W 120˚W 115˚W 110˚W 105˚W 100˚W 25˚N 30˚N 35˚N 40˚N 45˚N 50˚N 0 400 800 km Fig. 2. Correlation map between CTI and tree-ring chronologies of western North America. 4.6 DECADAL-SCALE CHANGES IN SOUTHERN CALIFORNIA TREE-RING RECORDS Franco Biondi (1) * , D.R. Cayan (1) (2) , and W.H. Berger (1) (1) Scripps Institution of Oceanography, La Jolla, California; (2) US Geological Survey, La Jolla, California 1. INTRODUCTION The PDO (Pacific Decadal Oscillation) and CTI (Cold Tongue Index) indices have been used to represent decadal-and ENSO-scale patterns in the Pacific basin (Mantua et al. 1997). Both indices are derived from sea surface temperatures, and their spatial correlation patterns with tree-ring chronologies over western North America (Figs. 1 and 2) show some similarities, but differ in Southern California. We have used a network of existing and newly developed chronologies for Southern and Baja California to investigate multi-annual oscillations of climate at the eastern Pacific boundary. 2. MATERIALS AND METHODS Tree-ring sites were located in a direction roughly parallel to the coastline, from the Transverse Mts. of Southern California to the Peninsular Ranges extending across the US-Mexico border to Sierra San Pedro Martir in northern Baja California (Fig. 3, Appendix). We developed the majority of those 10 chronologies; a few sites were sampled by Dave Meko, Laboratory of Tree-Ring Research, University of Arizona, Tucson, and one site was combined with a previous collection made by A. Douglas and available from the ITRDB. Jeffrey pine (Pinus jeffreyi) was the species sampled in more than half the sites (Fig. 4; Appendix); the other species were big-cone Douglas-fir (Pseudotsuga macrocarpa) and sugar pine (Pinus lambertiana). Measured ring-width series (‘segments’) were combined by site and species to produce tree- ring chronologies. Mean segment length (Cook et al. 1995) ranged between 112 and 355 years, with 11- 56 segments in each chronology. Tree-ring indices were computed as ratios between ring widths and their expected value based on the age/size trend (Fritts 1976). Autocorrelation (Box and Jenkins 1976) was not removed, in order to preserve multi- annual variability. Monthly precipitation and temperature records used for calibration with tree- ring chronologies were obtained from on-line databases (NOAA 1997; Fig. 1). * Corresponding author address: Franco Biondi, Univ. of California-San Diego, Scripps Inst. of Oceanography, La Jolla, CA 92093-0215; e-mail: fbiondi@ucsd.edu.