HR: 0800h
AN: GC21A-0152    [Abstracts]
TI: Detection and Attribution of temperature changes in the mountainous western United States.
AU: * Bonfils, C
EM: bonfils2@llnl.gov
AF: Lawrence Livermore National Laboratory, PO Box 808, Mail Stop L-103 7000 East Avenue, Livermore, CA 94550, United States
AU: Santer, B D
EM: santer1@llnl.gov
AF: Lawrence Livermore National Laboratory, PO Box 808, Mail Stop L-103 7000 East Avenue, Livermore, CA 94550, United States
AU: Pierce, D W
EM: dpierce@ucsd.edu
AF: Scripps Institution of Oceanography, Scripps Institution of Oceanography, La Jolla, CA 92093-0224, United States
AU: Bala, G
EM: bala@llnl.gov
AF: Lawrence Livermore National Laboratory, PO Box 808, Mail Stop L-103 7000 East Avenue, Livermore, CA 94550, United States
AU: Barnett, T P
EM: tbarnett-ul@ucsd.edu
AF: Scripps Institution of Oceanography, Scripps Institution of Oceanography, La Jolla, CA 92093-0224, United States
AU: Hidalgo, H G
EM: hhidalgo@ucsd.edu
AF: Scripps Institution of Oceanography, Scripps Institution of Oceanography, La Jolla, CA 92093-0224, United States
AU: Wood, A W
EM: aww@hydro.washington.edu
AF: University of Washington, Hydrology and Water Resources Engineering 111 Wilson, Box 352700, Seattle, WA 98195-2700, United States
AU: Dettinger, M
EM: mdettinger@ucsd.edu
AF: USGS, Scripps Institution of Oceanography, Dept 0224, 9500 Gilman Drive, La Jolla, CA 92093-0224, United States
AU: Cayan, D R
EM: dcayan@ucsd.edu
AF: Scripps Institution of Oceanography, Scripps Institution of Oceanography, La Jolla, CA 92093-0224, United States
AU: Cayan, D R
EM: dcayan@ucsd.edu
AF: USGS, Scripps Institution of Oceanography, Dept 0224, 9500 Gilman Drive, La Jolla, CA 92093-0224, United States
AU: Mirin, A
EM: mirin@llnl.gov
AF: Lawrence Livermore National Laboratory, PO Box 808, Mail Stop L-103 7000 East Avenue, Livermore, CA 94550, United States
AU: Das, T
EM: tadas@ucsd.edu
AF: Scripps Institution of Oceanography, Scripps Institution of Oceanography, La Jolla, CA 92093-0224, United States
AB: Under climate change, one of the major challenges that water managers face in the western United States is adequately meeting the water demand while minimizing the flood risk. It has been shown that, in the second half of the 20th century, winters and springs have warmed, the partition of precipitations has changed, the snow pack melts earlier and that the timing of streamflows has shifted towards the winter. A better understanding of the primary causes of these changes are crucial to reliably project future water availability. Hydrological changes can be driven by temperature or by precipitation changes, or a combination of the two. In this study, which is part of a more integrated analysis focusing on the detection and attribution of changes in the hydrological cycle, we raise the following questions: What are the causes of temperatures changes in the mountainous regions in the second half of the 20th century? Can we verify whether the observed earlier melting of snow is driven by human-induced temperature changes, rather than by changes in precipitation or natural internal climate variability? To address these questions, we conduct a detection and attribution analysis based on daily minimum and maximum temperatures, and on temperature variables that are more relevant to a potential shift in snowmelt (number of frost days and number of degree-days below 0C). We find that natural internal climate variability alone cannot explain the increase in temperature, the reduction of frost days and the decline in degree-days below 0C. External forcings agents such as the solar variability and volcanic eruptions cannot explain those changes either. Instead, we find a positive detection when the influence of anthropogenic greenhouse gases and sulphate aerosols effects are included in the climate forcings.
DE: 0740 Snowmelt
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 3337 Global climate models (1626, 4928)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting