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
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
April 2012
Study Area
East River Watershed
(89,600 acres)
April 2012
Climate Change, Extreme Events,
and Flooding
 Climate modeling for Great Lakes region and for
Wisconsin:
 By mid-century…
 Temps 2.0-4.0° C higher than 1960-90 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
April 2012
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
100-Year Floodplain in the ERW
April 2012
Scenes from the East River Watershed
April 2012
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:
Our Focus
 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
April 2012
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)
April 2012
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
April 2012
Estimated Benefits and Costs
Average Annualized Loss
Current Land Use
(2010)
Future Land Use
(2025)
$19.43 million
$22.06 million
Benefits
$2.63 million
833 parcels, 7,403 acres
Annualized Costs:
• Fee simple purchase… $5.1 million
• Easements… approx. $3.1 million
About 1/3 of the
land projected
to be developed
Benefits < Costs
April 2012
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)
April 2012
Costs Under Alternative Scenarios
Scenario 1:
Scenario 2:
targeting based targeting based on
on flood depth flood depth and
parcel acreage
Scenario 3:
targeting based on
costs, flood depth,
and parcel acreage
Annualized cost, fee
simple purchase
$3.67 million
$1.15 million
$496,000
Annualized cost,
easement purchase
$2.20 million
$690,000
$298,000
575
328
417
4,646
6,385
6,379
Number of parcels
Acreage
April 2012
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
Land Use Patterns: Alternative Scenarios
Baseline
Scenario 2:
Targeting Based on Flood Depth & Acreage
March 11
Refining the Approach
 Hazus
 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
April 2012
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
April 2012
Thank you!
Questions/comments: walls@rff.org
Report available at
http://www.rff.org/News/Features/Pages/GreenInfrastructures-Role-in-Adaptation-to-ClimateChange.aspx
NOAA Coastal Services Center’s Digital Coast:
http://www.csc.noaa.gov/digitalcoast/