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u <br />temperature will affect both crops and natural vegetation by reducing soil moisture. <br />These same effects will reduce runoff, which will in turn reduce streamflows and the <br />inventory of stored water, with the result that both natural and man -made systems will <br />experience reduced water supplies. <br />Because projected changes in climate are unprecedented in the historical record, the <br />only way to quantify future drought regimes is by modeling. The Colorado River Water <br />Availability Study (CRWAS), now being conducted by the Colorado Water Conservation <br />Board, will provide the information necessary to quantify the impact of climate change <br />on water availability for both natural and human uses. CRWAS will provide estimates of <br />water availability from runoff at hundreds of diversions and stream reaches throughout <br />the Colorado River Basin in Colorado (drought represents a shortage of water available <br />for a use). Data from the CRWAS project could be used to estimate soil moisture levels <br />throughout the Colorado River basin in order to evaluate impacts on natural vegetation <br />(CRWAS will provide estimates of changes in water requirements for irrigated crops). <br />Accordingly, data produced by CRWAS could be extended cost - effectively to inform <br />analysis of future drought conditions. However, this information is only available at this <br />time for that portion of Colorado within the Colorado River Basin. <br />CRWAS relies on the StateMod models and HydroBase database of the Colorado River <br />Decision Support System to quantify water availability at diversion points and stream <br />reaches. This capability is not available for the North Platte, South Platte and Arkansas <br />River basins, so extension of the CRWAS -type of analysis to the rest of the state cannot <br />be done cost effectively at this time. An acceptable approximation of impacts on water <br />availability could be done by extending the hydrologic modeling approach used in <br />CRWAS to the rest of the state, and reporting only changes in runoff and soil moisture. <br />Extension of the CRWAS alternate hydrology approach to the remainder of the state <br />would be straightforward. The approach would involve only changing the model spatial <br />domain to include the entire state of Colorado, running the eleven cases (one baseline <br />case and five projections each at two future time frames), and reporting changes in <br />runoff and soil moisture at a basin level. The estimates of changes in runoff and soil <br />moisture could be related to water availability impacts determined by CRWAS in the <br />Colorado River Basin, which might provide some further insight into impacts on water <br />availability in other parts of the state. <br />Once Colorado Decision Support Systems are available for other basins then water <br />availability estimates could be made in those basins. (The Rio Grande Decision Support <br />System exists; the South Platte Decision Support System is under development; and <br />the Arkansas Decision Support System is the subject of a feasibility study.) <br />AMEC will work with CWCB to define an application of the CRWAS results and <br />modeling framework to the drought vulnerability study. The goal will be to demonstrate <br />the utility of using CRWAS projections to more fully understand the potential future <br />impacts of drought under climate change conditions. We will apply the CRWAS -based <br />approach to one sector (e.g. agriculture or water supply) and for one basin (e.g. the <br />Colorado, or we can extrapolate CRWAS results to the South Platte basin). In this <br />manner we can focus on one demonstration example and fully flesh out related issues <br />such as the degree to which social and economic impacts of drought may be <br />