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Structure and Origins of Trends in Hydrological Measures over the western United States [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 2008.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
PDF-file: 48 pages; size: 1.8 Mbytes
Additional Creators
Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
This study examines, at 1/8 degree spatial resolution, the geographic structure of observed trends in key hydrologically relevant variables across the western United States (U.S.) over the period 1950-1999, and investigates whether these trends are statistically significantly different from trends associated with natural climate variations. A number of variables were analyzed, including late winter and spring temperature, winter-total snowy days as a fraction of winter-total wet days, 1st April Snow Water Equivalent (SWE) as a fraction of October through March precipitation total (P{sub ONDJFM}), and seasonal (January-February-March; JFM) accumulated runoff as a fraction of water year accumulated runoff. The observed changes were compared to natural internal climate variability simulated by an 850-year control run of the CCSM3-FV climate model, statistically downscaled to a 1/8 degree grid using the method of Constructed Analogues. Both observed and downscaled temperature and precipitation data were then used to drive the Variable Infiltration Capacity (VIC) hydrological model to obtain the hydrological variables analyzed in this study. Large trends (magnitudes found less than 5% of the time in the long control run) are common in the observations, and occupy substantial part of the area (37-42%) over the mountainous western U.S. These trends are strongly related to the large scale warming that appears over 89% of the domain. The strongest changes in the hydrologic variables, unlikely to be associated with natural variability alone, have occurred at medium elevations (750 m to 2500 m for JFM runoff fractions and 500 m-3000 m for SWE/PONDJFM) where warming has pushed temperatures from slightly below to slightly above freezing. Further analysis using the data on selected catchments across the simulation domain indicated that hydroclimatic variables must have changed significantly (at 95% confidence level) over at least 45% of the total catchment area to achieve a detectable trend in measures accumulated to the catchment scale.
Report Numbers
E 1.99:llnl-jrnl-406809
llnl-jrnl-406809
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Note
Published through SciTech Connect.
08/22/2008.
"llnl-jrnl-406809"
Journal of Hydrometeorology, vol. 10, N/A, January 8, 2009, pp. 871-892 10 FT
Pierce, D W; Barnett, T P; Das, T; Bala, G; Mirin, A; Cayan, D R; Dettinger, M D; Hidalgo, H G; Bonfils, C.
Funding Information
W-7405-ENG-48
View MARC record | catkey: 14130072