USGS to Develp Indicators to Better Measure Nation's H2O Supply: Greenwire

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regional water budgets, however, is commonly limited. To meet these information needs, the program will provide regional estimates of selected water - budget components. These estimates will support analyses of water availability that are undertaken by local and regional agencies, benefit research quantifying variability and changes in the national and global water cycle, and aid in the interpretation of trends identified in the national indicators of water storage, flow, and use. Because hydrologic, climatic, demographic, and other factors that affect water availability vary geographically, the relative importance of individual components of the water budget varies across the Nation. As a consequence, determination of improved regional water budgets will be tailored to the conditions that exist within the different Water Resources Regions. In some cases, large -scale models will be used to analyze current and historical changes in water budgets as well as regional trends in surface -water flows, ground -water storage, and ground -water discharge to surface water. These models also could serve as a regionwide framework for local studies and decision - making and provide a potential means for updating water -cycle components on frequent timescales. Network Evaluation An important consideration in the development of a set of water - related indicators is the extent and quality of the water - resource data - collection networks on which the indicators (and broader assessment) will be based. The process of computing water availability indicators from the basic data will help to identify uncertainties in our knowledge of the Nation's hydrologic conditions, and provide useful feedback to the design and improvement of data - collection networks. Data gaps identified by the program will be coordinated with improvements in data - collection networks for surface water and ground water defined by USGS plans for the National Streamflow Information Program, Ground - Water Resources Program, and as part of the Cooperative Water Program. A particular need for network evaluation exists with respect to ground water. As noted by Taylor and Alley (2001), a national program to systematically monitor and assess ground -water reserves or the sustainability of ground -water pumping does not exist. Moreover, according to a recent report on The State of the Nation's Ecosystems: Measuring the Lands, Waters, and Living Resources of the United States, data on ground- water levels and rates of change are "not adequate for national reporting" (H. John Heinz III Center, 2002). Networks of existing monitoring wells vary considerably across the country and the data are housed in many agencies. An inventory of existing water -level networks for major aquifer systems will be made early in the assessment to identify data gaps across the Nation. Selected wells will be identified for monitoring water levels to supplement existing networks where this is necessary for development of the indicators. The frequency of monitoring these wells will depend upon the magnitude of water -level fluctuations and could range from continuous for selected wells to annual or longer time periods between monitoring. Aggregated Information Warehouse A data warehouse will be established to provide a centralized location for aggregated information developed by the assessment. This information warehouse differs from the 12