United States Streamflow Probabilities and Uncertainties based on Anticipated El Niño, Water Year 2003 Michael D.Dettinger 1 Daniel R.Cayan 1 Kelly T.Redmond 2
1 U.S.Geological Survey,Scripps Institution of Oceanography,La Jolla,CA
2 Western Regional Climate Center,Desert Research Institute,Reno,NV
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During the course of spring and summer 2002, tropical sea-surface temperatures in the eastern Pacific Ocean have warmed and the wind and pressure fields have shifted, so that by August, there was considerable confidence that water year (October-September) 2003 will be characterized by a weak to mild El Niño climate.
Streamflow during historical El Niños may have been most notable for the variability that the warm events impart in many regions of the US. The range of streamflow conditions during past El Niños have been anomalously large in absolute terms in the Southwest, upper Midwest, and parts of the Southeast. The ranges have been large in relative terms in Northwest and Appalachian rivers.
In the midst of these uncertainties, there are nonetheless important regional signals. Historically, El Niño years have brought, on average, increases in mean flows (and flood sizes) in the Southwestern U.S. and east-central states, and decreases in the Northwest and parts of the Southeast (excluding Florida). Thus, drought conditions that currently exist in the Southwest could see some relief but there is reason for concern in the interior Northwest and in the mid-Atlantic states.
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