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persistent periods of wetness or dryness that occur over multi -year periods, beyond the normal <br />seasonal and year -to -year variability. Assessments of longer -term trends in surface -water <br />availability will help quantify regional changes associated with human activities and with <br />global climate and related environmental change. An example of the importance of such trend <br />information to water - supply management is given in Box A with respect to the effects of <br />changing temperature regimes on snowmelt - generated streamflow in New England and the <br />western States. <br />As part of the streamflow indicators, the program will provide an accounting of the status and <br />trends in the availability of water for instream uses in various parts of the country by defining <br />the amount of water remaining in a stream after offstream uses. The proposed program would <br />not estimate instream -flow requirements, because they can be estimated only by detailed <br />analysis of local situations. The program would, however, provide information on levels and <br />trends in seasonal flows and annual low flows, which are crucial to the instream -flow issue. <br />The indicators for storage changes will include surface reservoirs, selected natural freshwater <br />bodies, including large lakes such as the Great Lakes and Lake Champlain, perennial <br />snowfields, and glaciers. Development of indicators of surface -water storage will require close <br />coordination with other agencies and groups because most reservoir data are collected and <br />maintained primarily by agencies other than the USGS. <br />