Interannual Southern California Precipitation Variability During the Common Era and the ENSO Teleconnection

Southern California's Mediterranean‐type hydroclimate is highly variable on interannual time scales due to teleconnected climate forcings such as the El Niño–Southern Oscillation (ENSO). Here we present subannually resolved scanning X‐ray fluorescence Ti counts from deep‐sea cores in Santa Barbara Basin, California, recording 2,000 years of hydroclimate variability. The reconstructed Southern California precipitation record contains interannual variability in the 2‐ to 7‐year band that could be driven by changes in tropical Pacific ENSO variability and/or the strength of the ENSO teleconnection modulated by extratropical pressure systems. Observed interannual precipitation variance increased and was associated with longer periodicities (5–7 years) when the Intertropical Convergence Zone migrated southward (1370–1540 CE) and the Aleutian Low strengthened creating a robust ENSO teleconnection. Weak interannual precipitation variance with shorter periodicity (2–3 years) was observed when the Intertropical Convergence Zone shifted northward (700–900 CE) and/or the Aleutian Low was weak (1540–1680 CE). El Niños occur when the rising branch of atmospheric circulation in the tropical Pacific shifts eastward, driving changes in air temperature and rainfall around the globe. Rainfall in Southern California often increases during El Niño events causing rivers to carry extra sediment to the ocean. We reconstructed Southern California rainfall for every year of the last 2,000 years using the elemental signature of river sediment deposited in Santa Barbara Basin. We found that after ~1350 CE, when the Aleutian Low was strong, interannual rainfall in Southern California varied more and with longer cycles (5 to 7 years). During this time, the region of rising air at the equator was further south and storms over the North Pacific Ocean were stronger and occurred further east. Both of these changes in atmospheric circulation increased the Southern California rainfall response to El Niño events in the tropical Pacific Ocean. The interannual (2‐ to 7‐year band) precipitation in Southern California is closely related to ENSO variance originating from the tropical PacificExtratropical pressure systems modulate the interannual precipitation changes in Southern California by influencing the ENSO teleconnectionThe magnitude and frequency of interannual precipitation variance in Southern California changes throughout the past 2,000 years