Impact of Climate Change on Flow in the Upper Mississippi River Basin

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Image courtesy of NASA/GSFC
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Potential Climate Change Impacts on Flow and
Water Quality in the Upper Mississippi River Basin

• Eugene S. Takle
• Iowa State University
• Ames, IA 50011 USA
• gstakle_at_iastate.edu
• Project collaborators
• Manoj Jha, Zaitao Pan, Roy Gu

Iowa-Minnesota Drainage Research Forum 27
November 2007
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Outline

• Domain and hydrological model (SWAT)
• Calibration and validation
• Observations -gt stream flow
• NNR -gt RCM -gt SWAT-gt stream flow
• GCM -gt RCM -gt SWAT-gt stream flow
• GHG? -gt GCM -gt RCM -gt SWAT -gt stream flow
• Stream flow vs. precipitation

For details see Jha, M., Z. Pan, E. S. Takle,
and R. Gu, 2003 Impacts of climate change on
stream flow in the Upper Mississippi River Basin
A regional climate model perspective. Journal of
Geophysical Research.
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Sub-Basins of the Upper Mississippi River Basin
119 sub-basins Outflow measured at Grafton, IL
Approximately one observing station per
sub-basin Approximately one model grid point per
sub-basin
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Soil Water Assessment Tool (SWAT)

• Long-term, continuous watershed simulation model
  (Arnold et al,1998)
• Daily time steps
• Assesses impacts of climate and management on
  yields of water, sediment, and agricultural
  chemicals
• Physically based, including hydrology, soil
  temperature, plant growth, nutrients, pesticides
  and land management

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SWAT Output with Various Sources of Climate Input
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Calibration of SWAT Annual Stream Flow at
Grafton, IL
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Calibration of SWAT Monthly Stream Flow at
Grafton, IL
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Validation of SWAT Annual Stream Flow at
Grafton, IL
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Validation of SWAT Monthly Stream Flow at
Grafton, IL
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RegCM2 Simulation Domain
Red global model grid point
Green/blue regional model grid points
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Annual Stream Flow Simulated by SWAT Driven by
the RegCM2 Regional Climate Model with NNR
Lateral Boundary Conditions
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Mean Monthly Precipitation Simulated by the
RegCM2 Regional Climate Model with NNR Lateral
Boundary Conditions
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Seasonal Stream Flow Simulated by SWAT Driven by
the RegCM2 Regional Climate Model with NNR
Lateral Boundary Conditions
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Hydrological component comparison between RegCM2
and SWAT

RegCM2 SWAT
Evapotranspiration 588 528
Surface runoff 151 166
Snowmelt 256 240
Note All values are in mm per year averaged for
1980-1988 in NNR run.
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SWAT Output with Various Sources of Climate Input
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Ten-Year Mean Monthly Stream Flow Generated by
the RegCM2 Regional Climate Model Driven with
HadCM2 Global Model Results for the Contemporary
and Future Scenario (2040s) Climate
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Ten-Year Mean Precipitation Generated by the
RegCM2 Regional Climate Model Driven with HadCM2
Global Model Results for the Contemporary and
Future Scenario (2040s) Climate
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Errors in Simulated Stream Flow and Climate
Change
Comparisons Evaluate
SWAT 1 vs. Measured SWAT error
SWAT 2 vs. SWAT 1 RCM error
SWAT 3 vs. SWAT 2 GCM error

SWAT 3 vs. SWAT 1 GCM-RCM error
SWAT 2 vs. Measured RCM-SWAT error
SWAT 3 vs. Measured GCM-RCM-SWAT error

SWAT 4 vs. SWAT 3 Climate change
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Comparison of Simulated Stream Flow under
Climate Change with Various Model Biases
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Hydrologic Budget Components Simulated by SWAT
under Different Climates
Hydrologic budget components Calibration (1989-1997) Validation (1980-1988) NNR (1980-1988) CTL (around 1990s) SNR (around 2040s) Change (SNR-CTL)
Precipitation 856 846 831 898 1082 21
Snowfall 169 103 237 249 294 18
Snowmelt 168 99 230 245 291 19
Surface runoff 151 128 151 178 268 51
GW recharge 154 160 134 179 255 43
Total water yield 273 257 253 321 481 50
Potential ET 947 977 799 787 778 -1
Actual ET 547 541 528 539 566 5
All units are mm Yield is sum of surface runoff,
lateral flow, and groundwater flow
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Relation of Runoff to Precipitation for Various
Climates
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Regression Analysis Stream Flow vs.
Precipitation
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Water Quality(Results from GCM Study)

• Fugitive nitrates and sediment from the landscape
  are both carried by overland flow related to
  runoff
• The dominant pathway for nitrate loss is through
  leaching to groundwater and then via baseflow or
  tile drains (Randall, 2001).
• Results show a substantial decrease in runoff in
  the future climate but increase in baseflow,
  although with less agreement among models.

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Water Quality(Results from GCM Study)

• Both sediment and nitrate loading of streams
  would decrease due to decreased runoff but
  nitrate leaching might increase.
• Although water quality might improve due to
  reduced sediment, the loading due to nitrates is
  less clear but might increase.

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Summary

• RCM provides meteorological detail needed by SWAT
  to resolve sub-basin variability of importance to
  streamflow
• There is strong suggestion that climate change
  introduces changes of magnitudes larger than
  variation introduced by the modeling process
• Relationship of streamflow to precipitation might
  change in future scenario climates
• More research is needed to assess impact on water
  quality