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In the Pacific Northwest, warming climate has resulted in a lengthened growing season, declining snowpack, and earlier timing of spring runoff. This study characterizes the impact of climate change in two basins in Idaho, the Spokane River and the Boise River basins. We simulated the basin-scale hydrology by coupling the downscaled precipitation and temperature outputs from a suite of global climate models and the Soil and Water Assessment Tool (SWAT), between 2010 and 2060 and assess the impacts of climate change on water resources in the region. For the Boise River basin, changes in precipitation ranged from −3.8 to 36%. Changes in temperature were expected to be between 0.02 and 3.9°C. In the Spokane River region, changes in precipitation were expected to be between −6.7 and 17.9%. Changes in temperature appeared between 0.1 and 3.5°C over a period of the next five decades between 2010 and 2060. Without bias-correcting the simulated streamflow, in the Boise River basin, change in peak flows (March through June) was projected to range from −58 to +106 m3/s and, for the Spokane River basin, the range was expected to be from −198 to +88 m3/s. Both the basins exhibited substantial variability in precipitation, evapotranspiration, and recharge estimates, and this knowledge of possible hydrologic impacts at the watershed scale can help the stakeholders with possible options in their decision-making process

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This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found at JAWRA: Journal of the American Water Resources Association, published by Wiley-Blackwell. Copyright restrictions may apply. The definitive version is available at DOI: 10.1111/j.1752-1688.2011.00605.x