http://www.agu.org/meetings/fm09/program/abstract_submissions.php Precipitation trends in California: Rainfall is becoming wetter with heavier rain events

Recent U.S. climate data and climate model scenarios indicate that precipitation is increasing and heavy precipitation events are more numerous in most areas of the United States through the 20th Century. California records show some similarities to these results, but also some differences. By analyzing daily precipitation records from 20 California stations having continuous data from at least 1925 to present, we derived linear trends for both annual rainfall totals and for number of heavy rainfall events. Results vary with regions of the state. Annual precipitation amounts generally increased over the period of record for central and northern California, but did not change significantly in southern California. Year to year variability is large, especially to the drier south. The greatest percentage increases occur in the central region. All stations show a marked Pacific influence with ENSO and PDO signals showing prominently in the rainfall record, especially in southern California. Many stations, but not all, exhibit a shift towards higher daily rainfall amounts. They show decreases in the proportion of light rains and increases in moderate to heavy rains. Most stations indicate some change in seasonal rainfall totals. Increases in seasonal totals are found mostly in winter while decreases are occurring in fall. Spring trends are more varied and inconclusive. With the state in a long period of drought, the implications of these results for California water resources are unclear. While the state depends on the northern portions to meet much of the water demands, warmer temperatures may negate any precipitation increases through greater evaporation. Also negating the prospect of more water is the increased potential for flooding, particularly to the north.