Effectiveness of Low Impact Development for Managing Stormwater Under Changing Precipitation

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1 Effectiveness of Low Impact Development for Managing Stormwater Under Changing Precipitation Meredith Warren, USEPA, Global Change Research Program Christopher Pyke, Thomas Johnson, James LaGro, Jr., Jeremy Scharfenberg, Philip Groth, Randall Freed, William Schroeer, Eric Main September 28, 2011 The views expressed in this presentation are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.

2 National and Regional Climate Trends Increases in average annual temperature; exceeding records high temps Data source: NOAA NCDC (figures from EPA 2008 Report on the Environment)

3 National and Regional Climate Trends Precipitation pattern shifts Increase in magnitude of largest events 1 Current IDF curves may not represent more recent trends 2,3 1 Groisman et al. (2005) ; 2 Douglas and Fairbanks (2011), 3 Denault et al. 2006

4 National and Regional Climate Trends Changes in annual precipitation during last century 4 4 Data source: NOAA NCDC (figures from EPA 2008 Report on the Environment)

5 National and Regional Climate Trends Groisman et al. (2005)

6 Climate Adaptation Needs Stormwater management systems may not function as designed Need for local level vulnerability assessments Need for adaptation tools to prevent potential impacts 4 4

7 Research Objectives and Approach Explore climate and land interactions under changing precipitation Baseline understanding of LID as a potential climate change adaptation strategy Present scenarios approach for assessing potential impacts: land use and precipitation Use of simple stormwater runoff model to assess relationships and impacts

8 Land Use Scenarios South Weymouth Naval Air Station near Boston, MA closed with proposed redeveloped Site design scenarios: Conventional design Low impact design Open space Conventional and low impact design approved by local decision makers

9 Land Use Scenarios Design Attributes Conventional Low Impact Open Space Total site area (ha) Open space (% of total site) Impervious cover (% of total site) Estimated resident population 1,540 5,958 0 Development footprint (ha) Impervious cover (% of footprint) Total Roofs Parking Right-of-way

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11 Stormwater Model: SGWATER Simplified runoff model: CN Method for runoff EMCs used to calculate pollutant loads Annual runoff volume and loads of TN, TP, and TSS Screening level" assessment of different scenarios Limitations: No event or sub annual analyses No temperature adjustment capability Not suitable for comparing to other model outputs Not calibrated or validated model

12 Precipitation Scenarios Historical Observed precipitation events. V( 20) 20% volume decrease of all events. V(+20) I(10) I(45) I(10)+V(3) 20% volume increase of all events. 10% increase in precipitation occurring in the largest 5% of events; decrease smaller events. No net change in annual volume. 45% increase in precipitation occurring in largest 5% of events; decrease smaller events. No net change in annual volume. 10% increase precipitation occurring in largest 5% of events. 3% net increase in annual volume.

13 Precipitation Scenarios Event Bin Boundaries Percent Change in Event Intensity I(10) Percent Change in Event Intensity I(45) Percent Change in Event Intensity I(10)+V(3) >99.9 percentile percentile percentile >95 percentile Extrapolation of reported event intensity trends 20 and 90 years into future (Groisman et al., 2005) I(10), I(45), V(3) number represents volume increase

14 Results Simulations illustrate relationships between land use, changing precipitation, and stormwater. Low impact design resulted in significantly lower endpoint values versus conventional design Synergistic effect of increased precipitation and impervious cover on stormwater.

15 Land Use Scenario Indicator Historical I(10) I(45) V(-20) V(+20) I(10)+V(3) TSS (kg/ha/yr) Conventional Phosphorus (kg/ha/yr) Nitrogen (kg/ha/yr) Stormwater (m 3 /ha/yr) 2,634 2,697 3,025 1,709 3,666 2,829 TSS (kg/ha/yr) Low Impact Phosphorus (kg/ha/yr) Nitrogen (kg/ha/yr) Stormwater (m 3 /ha/yr) 1,869 1,928 2,242 1,173 2,665 2,028 TSS (kg/ha/yr) Open Space Phosphorus (kg/ha/yr) Nitrogen (kg/ha/yr) Stormwater (m 3 /ha/yr) , ,

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20 Relative Sensitivity Model

21 Conclusions Screening level assessment; need for more detailed event level analyses LID provides co benefits by increasing resilience to climate change. Identifies LID, specifically reduced impervious cover, as a potential no regrets adaptation strategy

22 Questions? Pyke et al. In press. Landscape and Urban Planning. Thanks to Oak Ridge Institute for Science and Education for supporting this project.