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
   

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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
   

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3. Precipitation, Urbanization, & Stormwater
   Source: nca2018.globalchange.gov/chapter/19
   2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022 03  35
   

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4. Source: nca2018.globalchange.gov/chapter/19
   2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022
   Precipitation, Urbanization, & Stormwater
   04  35
   

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5. Source: www.mrlc.gov/viewer
   2022 Virtual Urban Forestry Institute• FL Urban Forestry Council • March 11, 2022
   Precipitation, Urbanization, & Stormwater
   05  35
   

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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
   

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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
   

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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
   

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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
   

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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    Urban Forest Best Practices at the Macro Scale
    17  35
    

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    Urban Forest Best Practices at the Macro Scale
    18  35
    

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    Urban Forest Best Practices at the Macro Scale
    19  35
    

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    Urban Forest Best Practices at the Macro Scale
    20  35
    

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    Urban Forest Best Practices at the Macro Scale
    21  35
    

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    Urban Forest Best Practices at the Macro Scale
    22  35
    

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    Urban Forest Best Practices at the Macro Scale
    23  35
    

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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
    

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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
    

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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
    

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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
    

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    Urban Forest Best Practices at the Micro Scale
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    Urban Forest Best Practices at the Micro Scale
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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
    

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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
    

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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
    

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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
    

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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
    

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