HR: 11:35h
AN: U42B-06    [Abstracts]
TI: Pacific Ocean Forcing and the Development of Prolonged ‘Perfect Droughts' in Southern California and Adjacent Western North America Over the Holocene
AU: * MacDonald, G M
EM: macdonal@geog.ucla.edu
AF: Department of Geography, UCLA, 405 Hilgard Ave, Los Angeles, CA 90095-1524, United States
AB: A ‘perfect drought' in terms of southern California is defined here as a prolonged drought that impacts southern California and its major extra-regional water sources in northern California and the upper Colorado Basin. Instrumental climate records over the past century demonstrate that such super-regional droughts have occurred regularly, but generally persist less than 5 years. A notable example is the prolonged drought in the late 1980's - early 1990's which severely impacted southern California and areas northeastward to the midwestern United States and adjacent portions of the Canadian prairies. The core period of this drought from 1988 through 1990 was associated with cool conditions in the eastern tropical Pacific, and 40 to 50 degrees N latitude across the northern Pacific. During that time a persistent positive 700 mb height anomaly was anchored over the same region of the northeastern Pacific. Dendrohydrological estimates of the Palmer Drought Severity Index (PDSI) for southern California and annual discharge for the Sacramento and Colorado river systems for the past 1000 years indicate generally dry conditions during the Medieval period with two particularly notable periods of widespread ‘perfect drought' in the 11th and 12th centuries. Prolonged dry conditions in the west during this time can be linked through both empirical evidence and climate model experiments to the establishment of persistent cool sea surface temperatures (SST's) in the eastern tropical Pacific and northeastern Pacific. A Holocene length record of aridity obtained from lake sediments in the Sierra Nevada shows that such prolonged episodes of aridity have occurred prior to the last millennium and that prolonged aridity on the scale of centuries to millennia can directly be linked to variations in eastern Pacific SST's as resolved by paleoceanographic records.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4920 Dendrochronology
SC: Union [U]
MN: 2007 Joint Assembly