A tree-ring reconstruction of past precipitation for Baja California Sur, Mexico

There is great interest in the climatic variability of Baja California and the Sea of Cortes, but long-term information is limited because instrumenta l climate records begin in the 1940s or 1960s. The first tree-ring chronolo gy of Pinus lagunae was developed from the southern part of the Baja Califo rnia Peninsula and the chronology is used to reconstruct the history of pre cipitation variations. A September-July precipitation reconstruction is dev eloped for the period AD 1862-1996 (R = 0.71, p < 0.0001, n = 56, cross-val idation = 0.68. This reconstruction is used to assess precipitation variabi lity over the past two centuries, including the relationship with ENSO even ts. The reconstructed precipitation series indicates a long drought period from 1939 to 1958. It also shows that 1983, one of the strongest El Nino ev ents of the 20th century, is the wettest year. El Nino events during the 20 th century are associated with above-normal precipitation, whereas La Nina events are characterized by below-normal precipitation. Four of the most ex treme wet years occurred in association with these warm events (1905, 1912, 1919 and 1983). Seventy-one percent of La Nina events are characterized by below-normal precipitation. Sixty-two percent of Fl Nino events are charac terized by above-normal precipitation. Tree-ring growth of P. lagunae is mo st strongly correlated with winter precipitation in Sonora, Sinaloa and sou thern Baja California Sur. Precipitation data from meteorological stations in northern Baja California do not correlate well with the tree-ring chrono logy because this zone has a Mediterranean climate, which differs from the rest of northwest Mexico. Copyright (C) 2001 Royal Meteorological Society.