Urban Forests & the Urban Water Cycle

Presentation at 2022 Florida Urban Forestry Institute. Stormwater runoff and water pollution are major urban environmental challenges for many cities. Urbanization disrupts the natural water cycle in ways that may harm people, property, and the planet. Urban forests are a nature-based solution for restoring the urban water cycle while also providing a range of ancillary benefits such as shade, air purification, and carbon sequestration. In this presentation, you will learn about the urban water cycle, the role that urban forests play in restoring the cycle, and prevailing best practices for utilizing trees in stormwater management.

Transcript

1. Urban Forests & the Urban Water Cycle Principles and Practices for Utilizing Trees in Stormwater Management P. Eric Wiseman, PhD Associate Professor of Urban and Community Forestry Dept. of Forest Resources and Environmental Conservation Virginia Tech vtuf@vt.edu linktr.ee/EricWiseman @vtarborist 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022
2. Presentation Outline 02  35 o Science of precipitation, urbanization, and stormwater o The urban water cycle and role of trees in stormwater mitigation o Urban forest best practices for stormwater mitigation at the macro scale o Urban forest best practices for stormwater mitigation at the micro scale 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022
3. Precipitation, Urbanization, & Stormwater Source: nca2018.globalchange.gov/chapter/19 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 03  35
4. Source: nca2018.globalchange.gov/chapter/19 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Precipitation, Urbanization, & Stormwater 04  35
5. Source: www.mrlc.gov/viewer 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Precipitation, Urbanization, & Stormwater 05  35
6. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The developed land increase rates for each state between 2001 and 2016 Precipitation, Urbanization, & Stormwater 06  35
7. Source: www.mysuwanneeriver.com/151/Hydrogeology-Water-Quality-101 Source: www.nationalgeographic.org/photo/urban-water-cycle 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Precipitation, Urbanization, & Stormwater 07  35
8. IMPACTS OF IMPERVIOUS COVER • Consistently higher conductivity, dissolved organic carbon and filterable reactive phosphorus when EIA > 5%, 4%, and 1%, respectively. [Walsh et al. 2005b] • Invertebrate taxa sensitive to impervious cover lost when TIA between 2.5-15% in Piedmont streams and between 4-23% in Coastal Plain streams. [Utz et al. 2009] • Consistent channel instability when EIA > 10%. [Booth and Jackson 1997] • Sharp declines in macroinvertebrate diversity and richness when TIA between 8-12%. [Stepenuck et al. 2002] • Uniformly low summer baseflow when TIA > 40%. [Finkenbine et al. 2000] Source: www.mdpi.com/1424-8220/18/9/2873 Source: www.epa.gov/caddis-vol2/caddis-volume-2-sources-stressors-responses-urbanization-stormwater-runoff 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Precipitation, Urbanization, & Stormwater 08  35
9. Source: gicinc.org/trees_stormwater.htm 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 09  35 Source: gicinc.org/trees_stormwater.htm
10. Source: gicinc.org/trees_stormwater.htm The average depth of static water storage for tree foliage is 0.2 mm/unit leaf area (Wang and others 2008) Source: U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems and green stormwater infrastructure. FS–1146. Washington, DC. 23 p 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 10  35
11. Source: gicinc.org/trees_stormwater.htm A deciduous tree typically retains approximately 20 percent of the annual rainfall that falls on its canopy, while a conifer retains close to 30 percent (Kuehler and others 2017). A tree with 2,691 ft2 of leaf area could be expected to retain 1.8 ft3 of rainfall per rainfall event. This is equivalent to about 13 gallons of water. Source: U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems and green stormwater infrastructure. FS–1146. Washington, DC. 23 p 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 11  35
12. Source: gicinc.org/trees_stormwater.htm Source: U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems and green stormwater infrastructure. FS–1146. Washington, DC. 23 p 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 12  35
13. Source: gicinc.org/trees_stormwater.htm Source: U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems and green stormwater infrastructure. FS–1146. Washington, DC. 23 p 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 13  35
14. Source: gicinc.org/trees_stormwater.htm Source: Xiaoqing Shi, Tianling Qin, Denghua Yan, Fuqiang Tian, Hao Wang. (2021). A meta- analysis on effects of root development on soil hydraulic properties, Geoderma, Volume 403. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 The Urban Water Cycle & Urban Forests 14  35
15. Urban Forest Best Practices at the Macro Scale 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Source: www.newscientist.com/article/mg23831770-200-treeconomics-how-to-put-a-fair-price-tag-on-urban-forests URBAN FOREST ASSESSMENT URBAN FOREST POLICY URBAN FOREST PLANNING 15  35
16. Urban Forest Best Practices at the Macro Scale 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Source: www.charlottesville.gov/Archive/ViewFile/Item/97 16  35
17. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 17  35
18. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 18  35
19. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 19  35
20. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 20  35
21. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 21  35
22. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 22  35
23. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Macro Scale 23  35
24. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale SOIL o For trees • Rapid growth, larger trees, higher leaf area index, greater longevity o For water storage • Greater porosity, greater hydraulic conductivity o Rehabilitate soils degraded by urbanization o Use engineered soils in ultra-urban settings 24  35
25. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Ground Cover o Reduce impervious surfaces • Pavers or Permeable pavement o Increase permeable ground cover • Good: gravel • Better: turf • Best: mulch or litter o Goals: • Increase soil infiltration • Improve soil health • Improve tree root growth 25  35
26. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Tree Selection o Large-stature species o Species with high leaf surface area and leaf area index o Evergreen species o Diffuse-porous sapwood anatomy o Goals: • Increase canopy projection • Increase interception • Increase evapotranspiration 26  35
27. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Landscape Design o Plan for biodiversity o Use native species where practical o Create vertical structure and layers of vegetation o Use hydric and mesic species in space with lots of runoff o Create raingardens, bioswales, and riparian buffers to treat stormwater on-site and protect natural waters 27  35
28. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale 28  35
29. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale 29  35
30. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale 30  35
31. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Specify tree location, type, size, condition, and sunlight exposure 31  35
32. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Specify timeframe for calculating benefits 32  35
33. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Current year stormwater runoff benefits 33  35
34. 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Urban Forest Best Practices at the Micro Scale Cumulative stormwater runoff benefits over next 20 years 34  35
35. Take Home Messages o Climate change may bring more frequent and more intense rainfall to the southeastern US o Rapid urbanization leads to increases in impervious surfaces and losses of tree canopy, which lead to greater stormwater runoff o Trees mitigate stormwater runoff through canopy interception, soil infiltration, and evapotranspiration o Actions must be taken at the macro and micro scale to sustain tree canopy cover and maximize stormwater benefits of urban forests 2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 Source: massago.ca/2018/06/even-rainy-days-have-a-bright-side 35  35