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Effects of Different Methods for Computing Future Potential Evapotranspiration on Great Lakes Basin Hydrology and

Carlo DeMarchi Dept. of Earth , Environmental, and Planetary Sciences Case Western Reserve University Brent Lofgren NOAA Great Lakes Environmental Research Laboratory Qiang Dai Dept. of Civil and Environmental Engineering University of Michigan.

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Effects of Different Methods for Computing Future Potential Evapotranspiration on Great Lakes Basin Hydrology and

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  1. Carlo DeMarchi Dept. of Earth, Environmental, and Planetary Sciences Case Western Reserve University Brent Lofgren NOAA Great Lakes Environmental Research Laboratory Qiang Dai Dept. of Civil and Environmental Engineering University of Michigan Effects of Different Methods for Computing Future Potential Evapotranspiration on Great Lakes Basin Hydrology and Water Quality

  2. Summary • Different methodologies for computing PET in climate change scenarios: Temperature Adjustment vs. Energy Adjustment • Great Lakes water levels • Implications for navigability • Great Lakes tributary flow • Implications for water quality • Downscaling and non-linear processes • Assessing GCM driven performances Hydrologic Impacts of Climate Change Workshop 2012

  3. Traditional Evaluation of Climate Change Impact on Watershed Hydrology and WQ • Calibrate and validate hydrology and WQ models • Downscale present and future climate from GCM (Temperature, Precipitation, Relative Humidity, Wind) • Run hydro/WQ model with present and future GCM driven climate • Adjust results for known biases introduced by downscaled GCM climate Hydrologic Impacts of Climate Change Workshop 2012

  4. Problems of Traditional Approach • When PET is derived as a function of T only (e.g., PET=L eT/TB, Thornthwaite formula), the use of TGCM (or DTGCM ) can lead to an estimation of PET and thus of ET that is • inconsistent with GCM’s energy balance • A possible solution to this problem is adjusting the PET computed by the hydro/WQ model to match GCM PET Lofgren & Hunter 2011 Hydrologic Impacts of Climate Change Workshop 2012

  5. Impact of TA vs EA on River Discharge • The effect of TA in the LBRM model is an overestimation of PET, which leads to a strong decrease in river flow, despite the increased precipitation. • EA produces a river discharge which more similar to the Base case during the warm months Lofgren & Hunter 2011 Hydrologic Impacts of Climate Change Workshop 2012

  6. Impact of TA vs EA on Lake Levels: Average vs Extremes • Difference in 2081-2100 Lake elevation (TA –EA) • No clear pattern in difference in 90%-tile (higher) or in 10%-tile (lower) levels, but for the fact that the 10%-tile is more inconsistent. Hydrologic Impacts of Climate Change Workshop 2012

  7. Impact of PET Adjustment on Navigability: Lake Erie 1981-2000 GFDL2-A1B-TA 2081-2100 GFDL2-A1B-EA 2081-2100

  8. Impact of PET Adjustment on Navigability: Toledo (OH) 1981-2000 GFDL2-A1B-TA 2081-2100 GFDL2-A1B-EA 2081-2100

  9. Impact of PET Adjustment on Navigability: Duluth (MN) 1981-2000 GFDL2-A1B-TA 2081-2100 GFDL2-A1B-EA 2081-2100

  10. Impact of PET Adjustment on Water Quality: Maumee River Observed: 1,900 t/day GFDL2-EA: 2,106 t/day GFDL2-TA: 1,428 t/day

  11. Downscaling and Non-linear Processes Hydrologic Impacts of Climate Change Workshop 2012

  12. Effect of Spatial Scale of Precipitation on Erosivity Hydrologic Impacts of Climate Change Workshop 2012

  13. Need to Test Entire GCM+Downscale+Hydro/WQ Systems • Connection of different models is complex • Problem of scale may not be evident • Testing sub-system independently is necessary, but not sufficient • When system are GCM-driven, comparison can be done only in statistical way • Need of long term measurements • “Easy” for meteo/climate • Not so easy for WQ data • Not so easy for sub-surface Lake data Hydrologic Impacts of Climate Change Workshop 2012

  14. Assessing Great Lakes SST RCM Simulation • NDBC Buoys: 1980-2000 • SST (GL-SEA): 1967-2000 • LLTM (AHyPS): 1964-1993 Hydrologic Impacts of Climate Change Workshop 2012

  15. Hydrologic Impacts of Climate Change Workshop 2012

  16. Thanks for the attention! • Questions • Comments? • Suggestions? Hydrologic Impacts of Climate Change Workshop 2012

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