U.S. GEOLOGICAL SURVEY
                WATER-RESOURCES INVESTIGATIONS REPORT 93-4076

                         HYDRO-CLIMATIC DATA NETWORK
                                    (HCDN)
                        STREAMFLOW DATA SET, 1874-1988

                  [This is the \DOCFILES\OVERVIEW.DOC file]


                                   OVERVIEW

         BACKGROUND: The potential consequences of climate change to
      continental water resources are of great concern in the management
      of those resources.  Critically important to society is what
      effect fluctuations in the prevailing climate may have on
      hydrologic conditions, such as the occurrence and magnitude of
      floods or droughts and the seasonal distribution of water supplies
      within a region.  Records of streamflow that are unaffected by
      artificial diversions, storage, or other works of man in or on the
      natural stream channels or in the watershed can provide an account
      of hydrologic responses to fluctuations in climate.  By examining
      such records given known past meteorologic conditions, we can
      better understand hydrologic responses to those conditions and
      anticipate the effects of postulated changes in current climate
      regimes. Furthermore, patterns in streamflow records can indicate
      when a change in the prevailing climate regime may have occurred
      in the past, even in the absence of concurrent meteorologic
      records.

         A streamflow data set, which is specifically suitable for the
      study of surface-water conditions throughout the United States
      under fluctuations in the prevailing climatic conditions, has been
      developed.  This data set, called the Hydro-Climatic Data Network,
      or HCDN, consists of streamflow records for 1,659 sites throughout
      United States and its Territories.

         DEVELOPMENT OF THE HCDN DATA SET:  Records for the HCDN were
      obtained through a comprehensive search of the extensive surface-
      water data holdings of the U.S. Geological Survey (USGS), which
      are contained in the USGS National Water Storage and Retrieval
      System (WATSTORE).  All streamflow discharge records in WATSTORE
      through September 30, 1988, were examined for inclusion in the
      HCDN in accordance with strictly defined criteria of measurement
      accuracy and natural conditions.  No reconstructed records of
      "natural flow" were permitted, nor was any record extended or had
      missing values "filled in" using computational algorithms.  If the
      streamflow at a station was judged to be free of controls for only
      a part of the entire period of record that is available for the
      station, then only that part was included in the HCDN, but only if
      it was of sufficient length (generally 20 years) to warrant
      inclusion.  In addition to the daily mean discharge values,
      complete station identification information and basin
      characteristics were retrieved from WATSTORE for inclusion in the
      HCDN. Statistical characteristics, including the monthly mean
      discharge, as well as the annual mean, minimum and maximum
      discharge values, were derived for the records in the HCDN data
      set.

         CONTENTS OF THE HCDN DATA SET:  The HCDN includes data values
      for discharge measured at 1,659 streamflow gaging stations.
      Records cumulatively span the period 1874 through 1988, inclusive,
      and represent a total of 73,231 water years of information.

         Information necessary for the identification of each station in
      the HCDN, along with any qualifying comments about the available
      record for the site, and descriptive basin characteristics, are
      provided on this CD-ROM.

         [Taken from Landwehr, Jurate Maciunas, and Slack, J.R.,
         1992, Hydro-Climatic Data Network (HCDN): A U.S. Geological
         Survey streamflow data set for the United States for the
         study of climate fluctuations, 1874-1988: U. S. Geological
         Survey Open-File Report 92-632 (Water Fact Sheet), 2 p.]