El Niño-Southern Oscillation and precipitation history in Baja California: reconstruction using tree ring records

Tree ring records from northern Baja California were used for reconstructing annual series of precipitation and El Niño-Southern Oscillation. Reconstructions were compared to instrumental and historical records for verification. Five tree ring width chronologies were developed using standard dendrochronological and statistical techniques: one of Pinus coulteri, two of Pinus quadrifolia and two of Pinus jeffreyi. One of the latter updated an existing chronology and doubled its period of calibration with instrumental climatic data. The length of the chronologies was 101 to 551 years. All the chronologies had significant correlations with precipitation records from Ensenada, Baja California and San Diego, California and with an ENSO-related index based on instrumental records. Precipitation explained 8 to 57% of the variation in tree growth. Precipitation records were related to SOI (R2adj: 48 and 16% respectively), but tree ring chronologies captured weaker and more variable signals (R2adj : 3 to 24%). Agreement between historical documentary records and the tree ring reconstructed SOI with the highest predictive ability was 82%. Further research to extend the shorter reconstructed chronologies, which now show the strongest precipitation and ENSO signals, and further study of other sites and species from Baja California, is suggested.