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Strengths and Limitations of Long-term Streamflow Scenarios in the Southwestern United States
Water managers in the southwest United States face the challenge of securing sustainable supplies of fresh water over the next century. In the Colorado River basin, climatic change raises the risk of increased stress on water supplies due to decreases in snowpack, increasing evapotranspiration demand, depletion of soil moisture, and streamflow reductions. Because climate plays an important role in water supply availability, there is an increasing need for practical methods that incorporate climatic variability into water management practices. This project compares the strengths and limitations of six methods of developing time series for use in hydroclimatic scenarios: (1) index sequential method, (2) Monte Carlo sampling, (3) quantile mapping, (4) quantity-linked quantile mapping, (5) meteorology-linked quantile mapping, and (6) GCM climate projection adjustments. The six methods for developing time series represent increasingly interconnected linkages of the past (tree-ring based streamflow reconstructions), the present (gauge-based streamflow and instrumental meteorological records) and the future (climate projections based on GCMs). The strengths and weaknesses of the six methods are evaluated using a set of criteria that includes flexibility, underlying assumptions, ease of use, the ability to address nonstationarity, and impacts on the resulting hydroclimatic scenarios. In addition, a library of MatLab software code for the six methods will be developed in support of a paleo-toolkit for “Treeflow,” a website containing tree-ring reconstructions of streamflow for water management in the West: http://wwa.colorado.edu/treeflow/.