1. Image courtesy of NASA/GSFC

2. Potential Climate Change Impacts on Flow and Water Quality in the Upper Mississippi River Basin
Eugene S. Takle
Iowa State University
Ames, IA USA
Project collaborators:
Manoj Jha, Zaitao Pan, Roy Gu
Iowa-Minnesota
Drainage Research Forum
27 November 2007

3. Outline Domain and hydrological model (SWAT)
Calibration and validation
Observations -> stream flow
NNR -> RCM -> SWAT-> stream flow
GCM -> RCM -> SWAT-> stream flow
GHG -> GCM -> RCM -> SWAT -> 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.

4. Sub-Basins of the Upper Mississippi River Basin 119 sub-basins
Outflow measured
at Grafton, IL
Approximately one
observing station
per sub-basin
model grid point

5. 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

6. SWAT Output with Various Sources
of Climate Input

7. Annual Stream Flow at Grafton, IL
Calibration of SWAT:
Annual Stream Flow at Grafton, IL

8. Monthly Stream Flow at Grafton, IL
Calibration of SWAT:
Monthly Stream Flow at Grafton, IL

9. Annual Stream Flow at Grafton, IL
Validation of SWAT:
Annual Stream Flow at Grafton, IL

10. Monthly Stream Flow at Grafton, IL
Validation of SWAT:
Monthly Stream Flow at Grafton, IL

11. RegCM2 Simulation Domain
Red = global model grid point
Green/blue = regional model grid points

12. Annual Stream Flow Simulated by SWAT
Driven by the RegCM2 Regional Climate
Model with NNR Lateral Boundary Conditions

13. Mean Monthly Precipitation Simulated by
the RegCM2 Regional Climate Model
with NNR Lateral Boundary Conditions

14. Seasonal Stream Flow Simulated by SWAT
Driven by the RegCM2 Regional Climate
Model with NNR Lateral Boundary Conditions

19. 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 in NNR run.

20. SWAT Output with Various Sources
of Climate Input

23. 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

24. 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

25. 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

26. Comparison of Simulated Stream Flow under
Climate Change with Various Model Biases

27. Hydrologic Budget Components
Simulated by SWAT under Different Climates
Hydrologic budget components
Calibration
( )
Validation
( )
NNR
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
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

28. Relation of Runoff to Precipitation
for Various Climates

29. Stream Flow vs. Precipitation
Regression Analysis:
Stream Flow vs. Precipitation

30. 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.

31. 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.

32. 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