Margaret Walls. RFF First Wednesday Seminar. Green Infrastructure: Using Natural Landscapes for Flood Mitigation and Water Quality Improvements

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1 THE ROLE OF LAND USE IN ADAPTATION TO INCREASED PRECIPITATION AND FLOODING Margaret Walls RFF First Wednesday Seminar Green Infrastructure: Using Natural Landscapes for Flood Mitigation and Water Quality Improvements April 4, 2012

2 Background 2011 study by RFF researchers on how natural landscapes can help build resilience to climate change in particular, the increased flooding associated with more extreme events Co-authors: Carolyn Kousky, Sheila Olmstead, Molly Macauley, Adam Stern Case study: East River Watershed, near city of Green Bay, in Wisconsin s Lower Fox River Basin Funding from Great Lakes Restoration Initiative via NOAA Coastal Services Center Digital Coast Partnership

3 Study Area East River Watershed (89,600 acres)

4 Climate Change, Extreme Events, and Flooding Climate modeling for Great Lakes region and for Wisconsin: By mid-century Temps C higher than reference period Spring precipitation 15-25% higher (under high emissions scenario) Extreme events, Green Bay: 12% increase in 100-year, 24-hour precipitation events Heavy events greater than 3 inches see biggest increase Historical trends support the modeling Some serious flood events in recent years in the region Major water quality concerns

5 Land Use in the East River Watershed City of Green Bay 60% of land in ag Forecast: 46% increase in developed land use by 2025

6 100-Year Floodplain in the ERW

7 Scenes from the East River Watershed

8 Evaluating a Green Infrastructure Investment If land projected to be developed by 2025 is preserved instead what are the flood protection benefits? what are the costs? Flood protection benefits: Reduce exposure if less development, lower economic losses in a flood event Change hydrology less impervious surface, lower peak discharge and lower flood heights Costs land or easement purchase cost Our Focus

9 The Hazus Model GIS-based FEMA model that estimates damages from flood events Digital elevation model (DEM) is input for delineation of stream network Hydrology/hydraulics model generates flood surface elevation layer, which gives flood depth for given return periods (e.g., 100-yr flood) Inventory of structures at Census block level & depthdamage curves yield damages from flood events User can do a Level 1, 2, or 3 analysis o We do Level 2 some user-supplied data (including finer resolution DEM; parcel-level property info)

10 How We Use Hazus Estimate losses in future 2025 scenario with development as projected by county, for different flood events Estimate losses in alternative 2025 scenario with no development in floodplain Compute average annualized losses for each scenario Difference = an estimate of annual benefits from preserving land from development

11 Estimated Benefits and Costs Average Annualized Loss Current Land Use (2010) Future Land Use (2025) Benefits $19.43 million $22.06 million $2.63 million 833 parcels, 7,403 acres Annualized Costs: Fee simple purchase $5.1 million Easements approx. $3.1 million Benefits < Costs About 1/3 of the land projected to be developed

12 Targeting Three scenarios for targeting green infrastructure investments 1. Flood depth only parcels > 1 ft mean flood depth in 100-yr flood 2. Flood depth & parcel size only parcels that account for 90% of total acre-feet of flooding 3. Flood depth, parcel size, and costs only parcels below median cost per acre-ft of flooding (property value as measure of cost)

13 Costs Under Alternative Scenarios Scenario 1: targeting based on flood depth Scenario 2: targeting based on flood depth and parcel acreage Scenario 3: targeting based on costs, flood depth, and parcel acreage Annualized cost, fee simple purchase Annualized cost, easement purchase $3.67 million $1.15 million $496,000 $2.20 million $690,000 $298,000 Number of parcels Acreage 4,646 6,385 6,379

14 Comparing Targeting Scenarios to Baseline Scenario 2: 86% of the acreage at only 23% of cost Scenario 3: 86% of the acreage at 9.7% of cost Note: We have not recalculated benefits. However, these scenarios likely to pass benefit-cost test. March 11

15 Land Use Patterns: Alternative Scenarios Baseline Scenario 2: Targeting Based on Flood Depth & Acreage March 11

16 Hazus Refining the Approach Recalculate benefits for each scenario Level 3 analysis change the hydrology Less ad hoc targeting Include co-benefits recreation, water quality This is not easy Might highlight tradeoffs

17 Concluding Remarks Green infrastructure can provide flood protection benefits & build resilience to climate change But whether those benefits outweigh costs is not clear Likely to be specific to the setting Targeting may be critical Hazus model can provide a useful tool for estimating benefits Widely used by many communities But potential not fully tapped

18 Thank you! Questions/comments: Report available at Infrastructures-Role-in-Adaptation-to-Climate- Change.aspx NOAA Coastal Services Center s Digital Coast: