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1. Introduction
Along with the increase in global mean temperature at Earth’s surface over the twentieth century, the frequency of occurrence of storms, their spatial extents, and, most importantly, the mean and variance of storm precipitation intensity and duration have changed in many regions of the world (IPCC 2014; O’Gorman 2014). These changes in precipitation have led in some instances to catastrophic flooding or drought (Arnell 1999; Mahat and Anderson 2013; Zheng et al. 2009), as well as to changes in streamflow hydrographs at all spatial and temporal scales. Some recent flooding and drought, causing billions of dollars in damage and numerous fatalities, have been attributed partially to climate change (Smith and Katz 2013). As the climate changes, changes in timing and volume of snow accumulation and melt and streamflow pattern caused by it will impact water supplies. Indeed, failure of future water supplies is widely recognized as one of the greatest risks that humanity faces (World Economic Forum 2016). Assessment of future water supplies as the climate changes is thus of primary importance.
Global climate models in phase 3 of the Coupled Model Intercomparison Project (CMIP3), used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC 2007), provided the climate data for several hydrologic projections in the United States, including those for the upper Mississippi River basin (Jha et al. 2004), the Missouri River basin (Stone et al. 2001), the Columbia River basin (Hamlet and Lettenmaier 1999), the Hubbard Brook Experimental Forest in New Hampshire (Campbell et al. 2011), three major Western basins (Hidalgo et al. 2009), and the contiguous United States (CONUS; Foti et al. 2012, 2014). Hydrologic assessments based on the newer projections of twenty-first century climate generated by models in phase 5 of the Coupled Model Intercomparison Project (CMIP5; Sillmann et al. 2013; Taylor et al. 2012), used in the IPCC’s Fifth Assessment Report (AR5), are as yet less common. Sheffield et al. (2013a) reported improved representation of the mean and variance of precipitation and temperature with CMIP5 as compared to CMIP3; thus, CMIP5 projections should offer an improved basis for water supply assessments. See Sheffield et al. (2013a,b) and Sillmann et al. (2013) for an evaluation of the ability of CMIP5 models to replicate the...