• Open Access

Near-term acceleration of hydroclimatic change in the western U.S.

Authors

  • Moetasim Ashfaq,

    Corresponding author
    1. Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
    2. Woods Institute for the Environment and Department of Environmental Earth System Science, Stanford University, Stanford, California, USA
    3. Purdue Climate Change Research Center and Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
    • Corresponding author: M. Ashfaq, Oak Ridge National Laboratory, PO Box  MS6301, Oak Ridge, TN 37831-6301, USA. (mashfaq@ornl.gov)

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  • Subimal Ghosh,

    1. Department of Civil Engineering, Indian Institute of Technology, Bombay, India
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  • Shih-Chieh Kao,

    1. Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
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  • Laura C. Bowling,

    1. Purdue Climate Change Research Center and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA
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  • Philip Mote,

    1. Oregon Climate Change Research Institute and Oregon Climate Services, Oregon State University, Corvallis, Oregon, USA
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  • Danielle Touma,

    1. Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
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  • Sara A. Rauscher,

    1. Department of Geography, University of Delaware, Newark, Delaware, USA
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  • Noah S. Diffenbaugh

    1. Woods Institute for the Environment and Department of Environmental Earth System Science, Stanford University, Stanford, California, USA
    2. Purdue Climate Change Research Center and Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
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Abstract

[1] Given its large population, vigorous and water-intensive agricultural industry, and important ecological resources, the western United States presents a valuable case study for examining potential near-term changes in regional hydroclimate. Using a high-resolution, hierarchical, five-member ensemble modeling experiment that includes a global climate model (Community Climate System Model), a regional climate model (RegCM), and a hydrological model (Variable Infiltration Capacity model), we find that increases in greenhouse forcing over the next three decades result in an acceleration of decreases in spring snowpack and a transition to a substantially more liquid-dominated water resources regime. These hydroclimatic changes are associated with increases in cold-season days above freezing and decreases in the cold-season snow-to-precipitation ratio. The changes in the temperature and precipitation regime in turn result in shifts toward earlier snowmelt, base flow, and runoff dates throughout the region, as well as reduced annual and warm-season snowmelt and runoff. The simulated hydrologic response is dominated by changes in temperature, with the ensemble members exhibiting varying trends in cold-season precipitation over the next three decades but consistent negative trends in cold-season freeze days, cold-season snow-to-precipitation ratio, and 1 April snow water equivalent. Given the observed impacts of recent trends in snowpack and snowmelt runoff, the projected acceleration of hydroclimatic change in the western U.S. has important implications for the availability of water for agriculture, hydropower, and human consumption, as well as for the risk of wildfire, forest die-off, and loss of riparian habitat.

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