HR: 16:40h
AN: GC24A-03 INVITED    [Abstracts]
TI: Human Induced Changes in the Hydrological Cycle of the Western United States
AU: * Barnett, T P
EM: timdotbarnett@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Pierce, D W
EM: dpierce@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Hidalgo, H G
EM: hhidalgo@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Bonfils, C
EM: bonfils2@mail.llnl.gov
AF: Lawrence Livermore National Laboratory, PCMDI, L-103, Livermore, CA 94551-0808, United States
AU: Das, T
EM: tdas@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Santer, B
EM: santer1@llnl.gov
AF: Lawrence Livermore National Laboratory, PCMDI, L-103, Livermore, CA 94551-0808, United States
AU: Cayan, D
EM: dcayan@ucsd.edu
AF: Scripps Institution of Oceanography, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Cayan, D
EM: dcayan@ucsd.edu
AF: U.S. Geological Survey, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Dettinger, M
EM: mdettinger@ucsd.edu
AF: U.S. Geological Survey, Mail Stop 0224, La Jolla, CA 92093-0224, United States
AU: Bala, G
EM: bala@llnl.gov
AF: Lawrence Livermore National Laboratory, PCMDI, L-103, Livermore, CA 94551-0808, United States
AU: Mirin, A
EM: mirin@llnl.gov
AF: Lawrence Livermore National Laboratory, PCMDI, L-103, Livermore, CA 94551-0808, United States
AU: Wood, A
EM: aww@u.washington.edu
AF: University of Washington, Civil and Eviron. Engineering, Seattle, WA 98195-2700, United States
AB: INVITED Numerous studies have documented marked change in components of the hydrological cycle of the western United States over the last 50 or so years. The snow pack has decreased and been observed to melt earlier in the calendar year. Main spring river runoff has also been coming earlier in the year over the entire region, while air temperatures, especially in Spring, have increased. Previous studies have speculated that such changes are due to global warming. However, strong interannual variability and marked decadal fluctuations in weather patterns greatly affect the region, and previous studies have not performed a formal detection and attribution analysis of these changes, nor attempted to quantify the comparative effect of natural and anthropogenic forcing. In this study we have conducted a rigorous, multi-variate detection and attribution analysis with a variety of climate, regional and hydrological models to determine the causes of the recent changes in the western snowpack, large river flow and surface air temperature. Natural variability of the western climate system has been ruled out as the major cause of the changes. Similarly, changes in solar variability and volcanic impacts are also ruled out by the analysis. We find that the observed changes in the hydrological components mentioned above can be explained well by anthropogenic forcing (green house gases and aerosols) alone. This is the first time, to our knowledge, that regional changes in the hydrological cycle have been attributed rigorously to human induced forcing. Further, since the climate models used here simulated the last 50 years of observations well, we might do well to place stock in model predictions of future changes in the West. The current simulations suggest that within the next few decades, the western United States will face a ‘climate crisis' wherein its sustainability will be severely stressed.
DE: 1630 Impacts of global change (1225)
DE: 1637 Regional climate change
DE: 1655 Water cycles (1836)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting