This document summarizes a project that started as a stormwater study and expanded into a community resilience toolkit. The project quantified how trees mitigate stormwater runoff through hydrology modeling in pilot cities. Phase I included a technical report and handbook. Phase II created an online toolkit with resources on integrating urban forestry and stormwater management considering equity, climate change, and regional case studies. The toolkit provides a comprehensive collection of models, considerations, and resources to help communities collaborate across sectors to improve resilience.

1. From a Stormwater
Study to a Community
Resilience Toolkit
NOVEMBER 16, 2022
An Unexpected Journey to Make a Case
for Trees

2.  Overview of the Project Journey
 Exploration of Project Phase I
 Exploration of Project Phase II
 Review Resources
2
Presentation Outline

3. 3
The Journey
• Understand the role of forests in PNW hydrological cycle
• Goals
 Quantify the role of trees and forest cover in mitigating
stormwater runoff
 Compare and contrast two hydrology models
 Encourage a co-benefits strategy
• Prepare and Promote Resources
 Technical Report
 Handbook
 Regional Toolkit of resources

4. Phase I
Puget Sound Trees
& Stormwater Project
4

5. Trees and Stormwater 5

6. • Pilot City Tree Canopy
Assessments
• i-Tree Hydro and
WWHM Analysis and
Comparison
• Technical Report
• Handbook
Phase I Outputs 6
www.trees-and-stormwater.org

7. Section 1 - Multiple benefits of urban trees
Section 2 – Summary of Technical Report
Section 3 – Case Studies of collaboration
Section 4 – References and more Resources
Handbook 7

8. 8
Benefits: Stormwater Pre-Development

9. 9
Stormwater Post Development

10. Benefits: Carbon Cycle 10

11. Benefits: Urban Forest 11
Human Health
Air Quality
Mitigates Heat Island Effect
Wildlife
Habitat
Noise & Wind Buffer
Community
Livability
Equity
Biodiversit
y

12. • Four pilot communities
Kirkland, Tacoma, Snohomish, Kent
• Two hydrology models
i-Tree Hydro, WWHM
• Four spatial scales
city, drainage basin, neighborhood, site
• Three scenario variables
 Loss of tree canopy
 Change of canopy and land cover with
development
 Increase of tree canopy
Model Analysis Summary 12

13. Key Findings 13
1. Canopy Loss, Benefit Loss
2. Canopy over Impervious Surfaces
3. Tree Retention during Development
4. Higher Canopy Cover, Benefit Buffer
5. Runoff Volume-based Model
Comparison

14. 14
Scenarios where tree canopy is replaced (1A,
1B, 2A, and 2B) with any other land cover
type (herbaceous, shrub, impervious)
increases runoff volume.
Recommendation –
Retain and plant trees wherever
possible (overhanging impervious
areas, increasing canopy over pervious
areas) to reduce stormwater runoff
volume and pollution loads
Key Finding 1
Photo Credit: National Association of
Conservation Districts

15. 15
An increase in tree cover over
impervious surfaces results in
decreased runoff volumes.
Recommendation –
Plant trees to overhang
impervious surfaces for high
stormwater runoff and pollution
reduction benefits
www.seattleweekly.com/news/will-seattle-finally-protect-its-
tree-canopy
Key Finding 2

16. 16
Development that includes tree retention results in reduced
runoff volume compared with development without tree
retention.
Recommendation –
Retain existing trees during new
development and redevelopment
for higher stormwater runoff and
pollution reduction benefits
Key Finding 3
Photo Credit: Nashville Conservation Corps

17. 17
From Conversations to Collaboration

18. • Community Priorities
• Case Studies
• Co-Design for Co-Benefits
18
Collaboration Themes

19. 19
Section 4: Resource Compendium

20. Phase II
Community
Resilience Toolkit
20

21. Phase II - Toolkit 21
Trees & Stormwater Toolkit (2019)
Web-based compendium of resources for
municipal urban forestry and stormwater
collaboration
• Technical Report and Handbook
• Identify resource gaps
• Tree-related equity
• Resources for climate response
• Regional case studies and resources

23. Click to add text
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34. • Study to quantify tree canopy in mitigating stormwater runoff in
PNW
• Handbook encourages collaboration and co-design between urban
foresters and stormwater managers
• Explore the intersection of trees with equity, human health and
climate change…and beyond
• Toolkit
• Visual portrayal of how trees can be integrated into community resilience
• Comprehensive collection of resources, considerations and models by essential
components
• Two local success stories to demonstrate the different journeys to success
34
Project Journey

35. Snohomish CD
outreach@snohomishcd.org
Printed Handbook
35
Online Access to Toolkit, PDF Handbook & Technical Report​
www.betterground.org/urban-forests​
www.trees-and-stormwater.org
Printed Technical Report King CD
district@kingcd.org
Project Resources

36. This project has been funded wholly or in part by the United
States Environmental Protection Agency under assistance
agreement PC-01J18101 to the Washington State
Department of Ecology.
WA DNR Urban and Community Forestry  Washington Stormwater Center
Kathleen Wolf, PhD University of Washington
Pierce, King, Snohomish Counties - Surface Water
Puget Sound Conservation District Caucus
Pierce, King, Snohomish & Whatcom Conservation Districts
Phase I Pilot Cities of Kirkland and Tacoma
Cities of Snoqualmie and Edmonds
Stewardship Partners  The Nature Conservancy - Washington
King County - Cities Climate Collaboration (K4C)
And Funders!
36
Thank You Project Partners!

37. QUESTIONS?
37
Brandy Reed
b.reed@whatcomcd.org
District Manager
Whatcom Conservation District
Elizabeth Walker
ewtreelady@gmail.com
Principal
Terra Firma Consulting