Climate Change and Flooding in Wisconsin

1. 2011 WAFSCM Annual Conference November 3, 2011 - Pewaukee Climate Change and Flooding in Wisconsin Ken Potter Department of Civil & Environmental Engineering University of Wisconsin Madison, WI

2. Outline • Global Circulation (Climate) Models (GCMs) • WICCI findings based on statistical downscaling of GCMs • New findings based on Regional Circulation (Climate) Models (RCMs) • NOAA Atlas 14 • Storm transposition for vulnerability assessment

3. IPCC 2007 General Circulation Models • General Circulation Models (GCMs) • simulate the effects of incoming and outgoing thermal radiation on global circulation, and include: • Atmosphere • Clouds • Oceans • Topography • Rainfall • etc.

4. Dynamical Downscaling (Regional Circulation Models, RCMs) 3-hourly output, Many variables (T, P, H, SM, etc.) 6 RCMs driven by 4 GCMs North American domain Modern: 1970-2000 Future: 2038-2070 50 km horizontal resolution Climate Model Projections Daily output, Fewer variables (T, P, H?) Wisconsin domain Modern: 1950-2000 Future: 2001-2100 10 km horizontal resolution 20 GCMs Statistical Downscaling of GCM output

5. Wisconsin Initiative for Climate Change Impacts Downscaled (8x8 km) grid GCM grid D. Vimont, UW-Madison • Used 14 General Circulation Models (GCM’s) • from IPCC 2007 assessment • Debiased and downscaled using historical Wisconsin weather station data • Result: a statistical range of potential climate change Downscaling: Focus global projections to a scale relevant to climate impacts in Wisconsin

6. Temperature (°F) Change in average annual temp 1980 to 2055 Significant warming is projected

7. Precipitation Increase in 2” rainfalls 1980 to 2055 (days/decade) Change in annual average 1980 to 2055 (inches) 1.25” to 2.25” and 2-3 days/decade = modest future increase

8. Winter Precipitation 1980 to 2055 Increasing (water inches) Reduced Snowfall (%) Notaro et al. 2010 Precipitation as snow reduced by 20% by mid-century = 30% decrease in midwinter snow depth

9. Increased Winter Rainfall Potter and Liebl, 2010

10. DNR Cottle Vulnerability is already high during winter and spring Increased Winter-Spring Flooding? More rain in winter +More intense rainfall = More high water events? = More groundwater recharge? Gordy Stephenson

11. Quantile Projections: Madison Based on statistically downscaled data developed by Kucharik, Lorenz, Notaro, and Vimont, UW Madison.

12. Projected size of 100-year 24-hour storm for Madison, WI, based on 14 GCMs Schuster, et al ? Wetter or drier in summer ? Large Uncertainty in Rainfall Projections Which 100-year event doyou prefer ? 6”or 9”

13. What about Regional Circulation Models (RCMs)? • Recently developed by North American Regional Climate Change Assessment Program (NARCCAP) • 6 RCMs driven by 4 GCMs • North American domain • 1970-99; 2040-69 • 3-hourly output • 50 km resolution

14. RCM 100-Year, 24-Hour Rainfalls for Madison

15. RCM 100-Year, 24-Hour Rainfalls for Green Bay

16. RCM 100-Year, 24-Hour Rainfalls for Milwaukee

17. Quantile-Quantile Plots for Top 100 Daily RCM Rainfalls: Madison

18. Quantile-Quantile Plots forTop 100 Daily Rainfalls: Green Bay

19. Quantile-Quantile Plots forTop 100 Daily Rainfalls: Milwaukee

20. Quantile-Quantile Plot forTop 100 Daily Rainfalls: Milwaukee

21. What do others think about precipitation modeling? Science Magazine, October 2011: When the Seattle Public Utility asked University of Washington climate scientist Clifford Mass how big they should build the pipes in a $750M storm drainage system, he “couldn’t give them an answer.”

22. And a University of Wisconsin professor… In the same Science article, University of Wisconsin Professor Greg Tripoli points out that global circulation models can’t “create the medium-size weather systems that they should be sending into any embedded regional model.”

23. So what should we do about engineering design?

24. Hydrologic design is based on experience.(i.e. history) The record we use may actually reflect a drier period (TP40, 1938-1958). Are we designing for historical climate?

25. Provides data for locations South Beloit. IL More stations Longer period of record vs. TP-40 isohyetal maps NOAA Atlas 14Updating TP-40 TP-40 vs. NOAA Atlas 14 Record nYears (avg) Hourly Stations 200 vs. 994 14 vs. 40 Daily Stations 1350 vs. 2846 16 vs. 63 Revised statistical method

26. Davis Todd, et al 2006 NOAA Atlas 14 – Updated Design Storms Davis Todd, C.E., J.M Harbor, B. Tyner, Increasing Magnitudes and Frequencies of Extreme Precipitation Events Used for Hydraulic Analysis in the Midwest, Journal of Soil and Water Conservation, (61)4:179-184, 2006

27. NOAA Atlas 14 - a work in progress Midwest States - due late 2012 http://www.nws.noaa.gov/oh/hdsc/current_projects.html

28. What else can we do, given GCM uncertainties? Storm transposition can be used to asses vulnerability? The 2008 storm in the Midwest could be used this way.

29. Assess: • Floodplains and surface flooding • At-risk road-crossings • Stormwater BMPs • Sanitary sewer inflow and infiltration • Emergency response capacity • Wells and septic systems • Hazardous materials storage Vulnerability assessment “Build upon the experiences of communities that have experienced recent extreme rainfalls to guide a state-wide evaluation of vulnerabilities...” - WICCI Stormwater Working Group

30. Planning for impacts 25 or 50 years out is challenging Adaptation to low-risk high-cost events requires political support Can use simulations to understand high water impacts Building Long Term Resilience

31. Conclusions • Rain event intensities will likely increase in WI due to climate change, but the modeling results do not provide a sufficient basis for engineering design. • Winter-spring precipitation changes appear to be better supported. Runoff implications need further study.

32. Conclusions • NOAA Atlas 14 should be adopted statewide when available. • Storm transposition should be explored as a method of evaluating vulnerabilities and increasing resilience.

33. Questions?