Seasonality, spatial coherence and history of precipitation in a desert region of the Baja California peninsula

Precipitation patterns are characterized for an area of the Sonoran Desert in Baja California, with emphasis on temporal and spatial variability, based on nine stations between 30•03° and 28•58°, ca. 1953–1998. The interior stations formed a coherent region, while some distinct tendencies were shown for the Pacific and Gulf coasts. Precipitation was predominately in the cool season (61–91% in November–April), and was non-normal in both seasonal and annual totals. The duration of moist conditions was examined as the probability of some number of consecutive months above a threshold; for the cool season, the distributions approximated the Poisson with means dependent on the threshold. Spatial coherence was examined as the between-station correlation of inter-annual variation of seasonal totals. This also emphasized the cool-moist regime: the correlations of histories were all significant and exceeded 0•69 between interior stations, but most were weak or insignificant in the warm season. The full range of cool-season precipitation, showed a linear correlation with a seasonalized Southern Oscillation Index (−0•64) in the decades of record. Exceptionally, wet cool seasons were related to other proxy data; an historical reconstruction indicated very wet cool seasons were not evenly distributed in the last 150 years.