Image courtesy of NASA/GSFC

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@iastate.edu Project collaborators: Manoj Jha, Zaitao Pan, Roy Gu Iowa-Minnesota Drainage Research Forum 27 November 2007

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.

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

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

SWAT Output with Various Sources of Climate Input

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

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

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

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

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

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

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

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

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.

SWAT Output with Various Sources of Climate Input

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

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

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

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

Hydrologic Budget Components Simulated by SWAT under Different Climates Hydrologic budget components Calibration (1989-1997) Validation (1980-1988) 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

Relation of Runoff to Precipitation for Various Climates

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

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.

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.

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