1. Effect of Climate Change on Sewer Overflows in Milwaukee WEFTEC 2012 October 2012 Bridging the gap between climate change research and the risk of overflows from my collection system David Perry Brown and Caldwell, Milwaukee, Wisconsin

2. Presenter 2 David Bennett, Brown and Caldwell Urbain Boudjou, Tim Bate, and Karen Sands, Milwaukee Metropolitan Sewerage District Michael Hahn, Southeast Wisconsin Regional Planning Commission Sandra McLellan and Elizabeth Sauer, Great Lakes WATER Institute, University of Wisconsin, Milwaukee Co-Authors

3. Climate change research is producing a wealth of models and projections on global climate change … What does that mean to my organization in our local context? 3 What is the possible risk of overflows in the future? Will our long range facilities plans be ruined by climate change?

4. Milwaukee – our context Regional Climate Change Trends Downscaling: from Regional to Local Milwaukee Modeling System Findings Outline 4

5. Milwaukee – our context Some background to the key questions 5

6. Milwaukee Three rivers meet Lake Michigan 850 square miles drain to Milwaukee Harbor Pollution Sources: Urban runoff Agricultural runoff SSOs CSOs Great Lakes - 20% of Earth’s freshwater Drinking water source for 40M 500 beaches

7. Serves Milwaukee and 27 metropolitan communities 1 million people 5% Combined Sewers, 95% Separated Sewer Two large water reclamation facilities Total treatment capacity 690 MGD Deep Tunnel Storage – 427 MG CSO and SSO control Real Time Control Optimize use of treatment and storage Milwaukee Metropolitan Sewerage District 7

8. 2020 Facilities Plan Innovative watershed-scale approach – Collaborative, Integrated Wastewater system + water course system Improve water quality in regional streams/rivers and Lake Michigan. Facilities plan + Regional water quality management plan Completed in 2007 Did not account for climate change. Regional Water Quality Management Plan

9. 2020 Facilities Plan Regional Water Quality Plan Will the plan work if climate changes? Can we meet goals for SSO and CSO control?

10. Regional Climate Trends A few observations 10

11. How will our climate change? http://www.wicci.wisc.edu/climate-change.php Large events may become larger and more frequent Smaller events may become less frequent Total annual rainfall may be similar to existing – but the distribution of rainfall may vary

12. Probability of Snow vs. Rain Courtesy of Dan Vimont Only a 1-month snow season in Milwaukee later this century? Late 20 th c (1950-1999) Late 21st c (2080-2099) IPCC Scenario A2

13. Climate models and uncertainty Global Climate Models (GCM) 14 models Wide range in predicted results Strategy: Use two GCM models that represent the best and worse case scenario for our most sensitive season for generation of CSOs: SPRING RAINFALL

14. Downscaling to Local How to convert regional model results to local data 14

15. Climate Downscaling UW-Madison Center for Climate Research Approaches Statistical downscaling (GCM) Dynamic downscaling (regional climate models) Statistically downscaled precipitation and air temperature time series Projected mid-century climate change conditions Parent data: Milwaukee airport observed data for the 1940 through mid-2004 period. GCM Grid Cells Local 8 km x 8 km Grid cells

16. Milwaukee Modeling System How do we link climate projections to overflow estimates? 16

17. Modeling Methods used by MMSD 17 Rainfall and Meteorological Data Regional Hydrologic Model HSPF Continuous runoff and infiltration simulation (used for both wastewater and stormwater/watercourse modeling) Wastewater Flow Generation Model Flow Forecasting System (FFS) Calibrated wastewater hydrographs Wastewater Hydraulic Model MikeUrban Detailed simulation of level and flow in all pipes and facilities Simplified Wastewater Flow Generation and Hydraulic Model MACRO System-wide water balance simulation of flow and volume

18. Modeling Methods used by MMSD 18 Rainfall and Meteorological Data Regional Hydrologic Model HSPF Continuous runoff and infiltration simulation (used for both wastewater and stormwater/watercourse modeling) Wastewater Flow Generation Model Flow Forecasting System (FFS) Calibrated wastewater hydrographs Wastewater Hydraulic Model MikeUrban Detailed simulation of level and flow in all pipes and facilities Simplified Wastewater Flow Generation and Hydraulic Model MACRO System-wide water balance simulation of flow and volume Strong Hydrologic Foundation Decades of history rapidly simulated to predict SSOs and CSOs

19. Findings Will the plan work? 19

20. Case 1: 2010 Existing Facilities + Historic Climate Case 2: Recommended Facilities + Historic Climate Case 3: Recommended Facilities + DSN10% Case 4: Recommended Facilities + DSN90% Simulation Cases Population and Land Use Condition Facilities Represented in the Model Climate Scenario All cases used Projected Future 2020 Population and Land Use Baseline 2020 Facilities Plan Moderate climate change More extreme climate change

21. Simulated SSO Volume in Each Year 21 64 year simulation

22. Simulated SSO Volume in Each Year 22 64 year simulation

23. Simulated SSO Volume in Each Year 23 64 year simulation

24. Simulated CSO Volume in Each Year 24 64 year simulation

25. Simulated CSO Volume in Each Year 25 64 year simulation

26. Simulated CSO Volume in Each Year 26 64 year simulation

27. Average Annual Simulation Results 27

28. Large events may be larger and more frequent Small events may be less frequent The annual average rainfall may have a similar average amount Increasing spring rainfall is a characteristic of most GCM results Spring is also the time of greater CSO risk Increasing temperature may reduce the likelihood of snowmelt events Summary on climate change 28

29. Recommended Facilities in the 2020 Plan are designed to reduce overflows (especially SSOs) Year-to-year variability in overflows is large For both the existing climate and projected climate scenarios Climate change may increase CSOs Up to 20% more average annual CSO volume in the extreme climate scenario But annual SSO volume may not change significantly The objectives of the 2020 Plan are not significantly compromised in the climate change scenarios Additional facilities could be constructed to mitigate the changes Conclusions – for Milwaukee MSD 29

30. Build a team Climate researchers Hydrologic and hydraulic modelers Wastewater system planners and managers Water quality scientist Evaluation of climate change on overflows requires: Downscale GCM to local - statistically modify historic weather Model with strong hydrologic foundation Simulate long term response to climate scenarios Keep hydraulic model simple Conclusions – in general 30

31. David Perry Brown and Caldwell, Milwaukee, Wisconsin Presenter 31 David Bennett, Brown and Caldwell Urbain Boudjou, Tim Bate, and Karen Sands, Milwaukee Metropolitan Sewerage District Michael Hahn, Southeast Wisconsin Regional Planning Commission Sandra McLellan and Elizabeth Sauer, Great Lakes WATER Institute, University of Wisconsin, Milwaukee Co-Authors Let’s talk about it … I welcome your comments and questions