HR: 10:20h
AN: H32B-01 INVITED     [Abstracts]
TI: North American Drought Variability Reconstructed from Long Tree-Ring Records
AU: * Cook, E R
EM: drdendro@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9w, Palisades, NY 10964 United States
AB: Gridded summer Palmer Drought Severity Index (PDSI) reconstructions have been developed for most of North America using a network of centuries-long annual tree-ring chronologies. Many of the reconstructions extend back 1,000 years or more in the past, especially in the western United States (the West). Past droughts of unprecedented severity are indicated, especially prior to AD 1300, which make the current drought in the West since 1999 pale in comparison. Modeling experiments with an atmospheric general circulation model (AGCM) forced by observed global and tropical Pacific sea surface temperatures (SSTs) indicates that much of the observed and reconstructed North American drought variability can be accounted for by SST variations in the El Ni¤o-Southern Oscillation (ENSO) region. In particular, cool SSTs (La Ni¤a-like conditions) in the eastern tropical Pacific "cold tongue" region are associated with the development of drought conditions over large areas of North America. Modeling experiments using the Zebiak-Cane ENSO model forced by long-term changes in solar and volcanic activity also indicate that this region is very sensitive to small changes in radiative forcing. This finding may help explain how the AD 900-1300 interval of elevated aridity in the West developed and persisted. It also suggests that future increases in radiative forcing over the tropical Pacific due to greenhouse warming may promote the development of more droughts over North America in the future. More speculatively, there is statistical evidence for a persistent bi-decadal drought rhythm in the West since AD 800 in which the area affected by drought waxes and wanes with a mean period of ~20 years. It has been speculated that this phenomenon is caused by the interaction of solar and lunar tidal forcing with periods of 22 and 18.6 years, respectively. While this putative forcing of the climate system has not been demonstrated mechanistically, the existence of the bi-decadal drought rhythm over the past 1200 years in the West suggests that there is a physical basis for its existence.
DE: 1640 Remote sensing (1855)
DE: 1812 Drought
DE: 1833 Hydroclimatology
DE: 1869 Stochastic hydrology
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
SC: Hydrology [H]
MN: Fall Meeting 2005