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Impact of Climate Change on Hydrology and WQ of the Upper Mississippi River

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  • Mike Neuman
    Assessing the Impact of Climate Change on the Hydrology and Water Quality of the Upper Mississippi River , 14-16 November 2005 Eugene Takle, Iowa State
    Message 1 of 1 , Oct 9, 2006
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      "Assessing the Impact of Climate Change on the Hydrology and Water
      Quality of the Upper Mississippi River", 14-16 November 2005

      Eugene Takle, Iowa State University
      Manoj Jha, Iowa State University
      Christopher Anderson, NOAA Forecast Systems Laboratory
      Phil Gassman, Iowa State University

      ABSTRACT

      Recent observations and modeling suggests acceleration of the
      hydrological cycle at high latitudes in the Northern Hemisphere and
      that extreme intense precipitation events were more frequent over the
      last 30 years of the twentieth century. Assessments of local and
      regional impacts of changes in the hydrological cycle in future
      climates call for improved capabilities for modeling the hydrological
      cycle and its individual components at the subwatershed level. We
      have evaluated the impact of climate change on stream flow in the
      Upper Mississippi River Basin by use of a regional climate model
      (RCM) coupled with a hydrologic model - Soil and Water Assessment
      Tool (SWAT) - and by use of an ensemble of GCMs producing output for
      the IPCC 4th Assessment Report coupled to SWAT. Both the RCM and the
      GCM ensemble reproduce quite well the annual flow and interannual
      variability of observed streamflow of the UMRB for the 20th Century.
      Individual low-resolution GCMs give poor simulation of annual
      streamflow, but the one high-resolution GCM tested gave good results.

      The RCM driven by a single GCM (HadCM2) results for the decade of the
      2040s gave a 21% increase in future precipitation, which resulted in a
      51% increase in surface runoff, 43% increase in groundwater recharge,
      and 50% net increase in total water yield in the UMRB on an annual
      basis. Although there is inconsistency among GCMs, the ensemble-mean
      precipitation increased of 6% due to climate change. ET calculations
      give positive changes for all models, likely due to warm-season
      temperature increases.

      Substantial decreases in snowfall suggest that warming is strong in
      winter.

      Runoff decreases substantially for most models, possibly due to
      enhanced drying of soils between rains.Total water yield varied
      widely among models, with the ensemble mean showing almost no change
      from the contemporary climate.

      Fugitive nitrates and sediment are carried by overland flow related
      to runoff. However, the dominant pathway for nitrate loss is through
      leaching to groundwater and then via baseflow or tile drains. Results
      show a substantial decrease in runoff in the future climate but
      increase in baseflow, although with less agreement among models. From
      this we speculate that both sediment and nitrate loading of streams
      would decrease due to decreased runoff but that nitrate leaching
      might increase.Therefore, although water quality might improve due to
      reduced sediment, the loading due to nitrates is less clear but might
      increase.

      Published in "U.S. Climate Change Science Program Workshop 14-16
      November 2005: Climate Science in Support of Decision Making -
      Abstract Book", Arlington, Virginia, Page Number 91
      http://www.climatescience.gov/workshop2005/abstracts/CCSPworkshop2005-
      abstracts.pdf
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