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Widespread Increases in Streamflow

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  • Mike Doran
    News Release U.S. Department of the Interior U.S Geological Survey Release Date: May 5, 2005 Contact: A.B. Wade 703-648-4483 abwade@usgs.gov USGS Scientists
    Message 1 of 1 , May 6, 2005
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      News Release
      U.S. Department of the Interior
      U.S Geological Survey

      Release Date: May 5, 2005

      Contact: A.B. Wade 703-648-4483 abwade@...

      USGS Scientists Document Widespread Increases in Streamflow and
      Changes in the Timing of Snowmelt Over the Past 50 Years
      Reston, VA – U.S. Geological Survey (USGS) scientists have identified
      nationwide trends toward increasing streamflow in many areas of the
      nation since 1940 based on data collected from long-term USGS
      streamgages. This conclusion and several more interesting trends in
      our nation's streamflows can be found in four new fact sheets
      recently issued by the agency.

      "Understanding streamflow trends is essential to effective management
      of the nation's water supply and is critical to developing strategies
      that mitigate the potential negative impacts of floods and droughts,"
      said USGS Associate Director for Water Robert Hirsch.

      In the first study, USGS scientists identified a nationwide trend
      that streamflow has been increasing in the United States since at
      least 1940. Most of the increases were during low-and-moderate
      streamflows. This means that, during typically dry periods, more
      water is now available in the stream.

      In the second study, scientists discovered that over the last 30
      years, winter/spring streamflows occurred one to two weeks earlier
      than in previous decades in northern or mountainous areas of New
      England. Similarly, in the third study, scientists found that
      streamflows in most western rivers occur almost one to three weeks
      earlier now than they did in the middle of the 20th century.

      The fourth study shows that the streamflow of the Mississippi River
      was influenced by both climate and human activities such as
      construction of water reservoirs, agricultural irrigation and
      groundwater pumping. Streamflow of the Mississippi River increased at
      a rate of 4.5 percent per decade largely because of an increase in
      precipitation.

      The USGS has been measuring and recording streamflow in the United
      States since the late 1800's. Today, the USGS monitors streamflow at
      7,400 locations nationwide. The USGS streamflow information is used
      for many purposes such as water resource appraisal and allocation,
      design of the nation's infrastructure such as bridges and water
      treatment plants, flood hazard planning, National Weather Service
      flood forecasting, reservoir operations, water-quality management,
      habitat assessment and protection, recreational enjoyment and safety,
      and understanding changes in streamflow due to land-use and climate
      changes. USGS streamflow data are available at
      http://water.usgs.gov/waterwatch/.

      Summary of the Fact Sheets:

      Streamflow Trends in the United States
      (http://pubs.water.usgs.gov/fs2005-3017/)
      Streamflow has been increasing in the United States since at least
      1940. Regions that experienced the most widespread increases were the
      Upper Mississippi, Ohio Valley, Texas-Gulf, and the Mid Atlantic.
      · Of the nearly 22,700 streamgages for which the USGS has records,
      435 monitor natural basins and have records of sufficient length to
      analyze climatic trends.
      · Streamflow increased across most of the United States during the
      20th century at 40-45 percent of these 435 stations.
      · Increases were most prevalent in low to moderate streamflows (seen
      at 40 percent of the stations), with relatively few decreases (seen
      at 8 percent of stations).
      · Comparatively few stations (10 percent) had increases in annual
      maximum streamflow.
      · Streamflow increases occurred as a sudden rather than gradual
      change around 1970, suggesting the climate shifted to a new regime.

      Changes in Streamflow Timing in New England During the 20th Century
      http://pubs.water.usgs.gov/fs2005-3019/)

      During the last 30 years, the timing of winter/spring streamflow has
      shifted earlier by one to two weeks in northern and mountainous New
      England streams.
      · The date when half of the total volume of streamflow for
      winter/spring (January 1 to May 31) now arrives earlier than it did
      in the first half of the 20th century at 14 of 27 streamgages in New
      England.
      · This shift to earlier streamflow was evident at all of the gages in
      the northern and mountainous areas of Maine and New Hampshire where
      snowmelt has the greatest effect on streamflow (11 of the 27
      streamgages).
      · Only 4 of the 27 streamgages exhibited shifts in the timing of
      fall/winter streamflow (October 1 to December 31), and all of these
      tended toward earlier streamflow.

      Changes in Streamflow Timing in the Western United States in Recent
      Decades http://pubs.water.usgs.gov/fs2005-3018)

      As much as three-quarters of water supplies in the western United
      States are derived from snowmelt. Trends toward earlier snowmelt and
      streamflow need to be considered in the water-resource and flood-
      management systems and procedures in many western settings.
      · The average streamflow center-of-volume date (the date on which one-
      half of the total annual flow volume passes a streamgage) in the
      western United States is about nine days earlier now than in the
      1950s.
      · These shifts in timing result both from late winter and early
      spring temperature increases, and from changes in the form of
      precipitation (increasing liquid precipitation, smaller percentage of
      snow) in late winter and early spring.

      Trends in the Water Budget of the Mississippi River Basin, 1949-1997
      (http://pubs.water.usgs.gov/fs2005-3020/)

      This study involved analysis of trends in precipitation, streamflow,
      evapotranspiration, depletion of ground water, and the filling of
      reservoirs. This study describes the influences of both climate
      trends and human alterations on streamflow from 1949 to 1997.
      · Streamflow in the Mississippi River basin increased at a rate of
      4.5 percent per decade during the second half of the 20th century.
      · This increase resulted primarily from an increase in precipitation
      offset by increases in evaporation from reservoirs and irrigated
      cropland in the basin.

      The USGS serves the nation by providing reliable scientific
      information to describe and understand the Earth; minimize loss of
      life and property from natural disasters; manage water, biological,
      energy, and mineral resources; and enhance and protect our quality of
      life. Subscribe to receive the latest USGS news releases.

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