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Originally published in Science Express on 31 January 2008
Science 22 February 2008:
Vol. 319. no. 5866, pp. 1080 - 1083
DOI: 10.1126/science.1152538
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Reports

Human-Induced Changes in the Hydrology of the Western United States

Tim P. Barnett,1* David W. Pierce,1 Hugo G. Hidalgo,1 Celine Bonfils,2 Benjamin D. Santer,2 Tapash Das,1 Govindasamy Bala,2 Andrew W. Wood,3 Toru Nozawa,4 Arthur A. Mirin,2 Daniel R. Cayan,1,5 Michael D. Dettinger1,5

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climate change detection and attribution study, using a high-resolution hydrologic model forced by global climate models, focusing on the changes that have already affected this primarily arid region with a large and growing population. The results show that up to 60% of the climate-related trends of river flow, winter air temperature, and snow pack between 1950 and 1999 are human-induced. These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.

1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
2 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
3 Land Surface Hydrology Research Group, Civil and Environmental Engineering, University of Washington, Seattle, WA 98195, USA.
4 National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
5 U.S. Geological Survey, La Jolla, CA 92093, USA.

* To whom correspondence should be addressed. E-mail: tbarnett-ul{at}ucsd.edu

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