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The Value of Olympia’s Urban Trees for Stormwater Management

Item

Title

The Value of Olympia’s Urban Trees for Stormwater Management

Date

2023 July

Creator

Vu, Rachel

Identifier

Thesis_MES_2023_VuR

extracted text

THE ESTIMATED VALUES OF OLYMPIA’S
URBAN TREES FOR STORMWATER
MANAGEMENT USING A BENEFIT TRANSFER METHOD

by
Rachel M. Vu

A Thesis
Submitted in partial fulfillment
Of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
June 2023

©2023 by Rachel M. Vu. All rights reserved.

This Thesis for the Master of Environmental Studies Degree
by
Rachel Vu

has been approved for
The Evergreen State College
by

_______________________________
Kathleen Saul, Ph. D.
Member of Faculty

_______________________________
Date

ABSTRACT
The Estimated Values of Olympia’s Urban Trees for Stormwater Management Using a Benefit
Transfer Method
Rachel Vu
Urbanization creates a shift in landscape, replacing the natural environment with more
impervious surfaces. These surfaces prevent water from infiltrating into the ground, obstructing
with the environment’s natural hydrology while picking up harmful pollutants from anthropgenic
activity. This results in increased stormwater runoff and pollution, frequent and intesnse
flooding, and impacts on drinking water sources. Urban trees and other types of natural
infrastructure are known to have significant benefits in mitigating and treating stormwater.
Unfortuantely, Olympia lacks data on green stormwater infrastructure, therefore little is known
about Olympia’s urban trees’ role in stormwater management. Using a benefit transfer method
from the city of Snoqualmie’s 2020 Natural Infrastructure Assessment, I was able to estimate the
annual dollar value per acre of Olympia’s urban trees. I found that Olympia’s urban trees are
estimated to bring a significant amount of economic prosperity and savings in water quality if
they are continued to be protected and healthy. These results not only show the importance of
urban trees and natural infrastructure, but can also encourage more research on the unknown
benefits of Olympia’s urban trees.
Key Words: Urban Trees, Green Infrastructure, Urbanization, Stormwater

Table of Contents
Table of Contents ...................................................................................................................................... iv
List of Figures .............................................................................................................................................. v
List of Tables .............................................................................................................................................. vi
Acknowledgments .................................................................................................................................. vii
Introduction ................................................................................................................................................. 1
Literature Review ...................................................................................................................................... 3
1.1 Green Infrastructure vs Grey Infrastructure ................................................................................. 3
1.1.1 Definitions .................................................................................................................................................................................. 3

1.2 Urbanization Impacts on Stormwater .............................................................................................. 5
1.2.1 More Development, More Impervious Surfaces ......................................................................................................... 5
1.2.2 Implications of Less Greenspace ....................................................................................................................................... 6

1.3 Climate Change Projections in Western Washington ................................................................ 12
1.3.1 General Climate in Western Washington ................................................................................................................... 12
1.3.2 Future Changes in Extreme Precipitation and Flooding ...................................................................................... 12

1.4 Urban Ecosystem Services and Benefits ........................................................................................ 13
1.4.1 Ecological Benefits ............................................................................................................................................................... 14
1.4.2 Social Benefits ........................................................................................................................................................................ 17
1.4.3 Economic Benefits ................................................................................................................................................................ 19

1.5 Significance of Urban Trees ............................................................................................................... 22

Methods ...................................................................................................................................................... 24
Results and Discussion ......................................................................................................................... 28
Yauger Park Case Study .............................................................................................................................. 30
Economic Footprint ...................................................................................................................................... 33
Benefits ............................................................................................................................................................ 35
Limitations ...................................................................................................................................................... 36

Conclusion ................................................................................................................................................. 38
References ................................................................................................................................................. 40

iv

List of Figures
Figure 1 ............................................................................................................................................ 8
Figure 2a-b....................................................................................................................................... 9
Figure 3 .......................................................................................................................................... 11
Figure 4 .......................................................................................................................................... 21
Figure 5 .......................................................................................................................................... 30

v

List of Tables
Table 1 ........................................................................................................................................... 15
Table 2 ........................................................................................................................................... 29
Table 3 ........................................................................................................................................... 29
Table 4 ........................................................................................................................................... 31
Table 5 ........................................................................................................................................... 32
Table 6 ........................................................................................................................................... 32
Table 7 ........................................................................................................................................... 34

vi

Acknowledgments

My thesis reader, Kathleen Saul, for all their guidance, continuous support, invaluable advice,
and patience throughout my research.
All the people I have met at MES, especially my peer review group, Marlene Melchert, Megan
Folkers, and Renae Bosivert, for their endless emotional support and reminding me I am not
alone in this challenging journey.
The Snoqualmie Natural Infrastructure Assessment project team, Lance Davisson and Zac
Christin, without whom I would not have been able to do this research.
My friends and family who have supported me throughout the many years of my educational
journey.
Lastly, thank you urban trees for clean air, water, and the many other ecosystem services you
provide for humans. Your silent beauty and values will no longer be overlooked and under
appreciated.

vii

Introduction
More than half of the world's population lives in cities and cities will house most of the
population growth over the next four decades (United Nations, 2018). The increase in urban
population poses many challenges and increases environmental pressures. In the United States,
for example, urban tree canopy cover is projected to decline at a rate of about four million trees
per year due to rapid urbanization along with tree diseases due to climate change (Wolf et al.,
2020). These losses in land cover caused by urbanization trigger negative impacts on
downstream ecosystems, hydrological functions, and urban communities. In fact, the degree of
urban and suburban land use has been correlated with increases in flood intensity and frequency,
peak flow, runoff volume, and pollutant yield (Woznicki et al., 2018). This growth and the
associated changes in urban form, land use, and population growth have already produced
environments that present several threats to ecosystem services and local communities (Felappi,
2020; Soz et al., 2016). Ecosystem services such as air and water quality, flood risk reduction,
and waste treatment are all provided by green infrastructure. Without green infrastructure, these
services, which are the foundation of economic and social importance, would not be beneficial
(Caparros-Martinez et al., 2020; Nowak et al., 2014). Green infrastructure, specifically urban
forests has emerged as a multifaceted strategy for transforming urban spaces to establish more
habitable, healthy, and wildlife-friendly cities (Felappi, 2020).
According to the Environmental Protection Agency (EPA), urban stormwater is a
significant reason why half of the United States rivers and streams don’t meet national water
quality standards put forth by the Clean Water Act (Denchak, 2019). Urban lakes and estuaries
also fail to meet water quality standards, including Olympia, WA’s Budd Inlet and Capitol Lake.

1

As a result, rapid urbanization without consideration of green space puts ecological functions and
ecosystem services at risk (Monteiro et al, 2020).
This study aims to shed light on the advantages of urban trees and forests for stormwater
runoff management in Olympia, WA, and was developed with two goals in mind: (1) What
ecosystem services related to stormwater are provided by Olympia’s urban trees and (2) What
are the associated economic benefits of Olympia’s urban trees in reducing nutrient contamination
of stormwater, specifically to understand whether green infrastructure is a valuable component in
management practices. Considering Olympia lacks data on green infrastructure stormwater
management practices, Snoqualmie’s 2020 Natural Infrastructure Assessment was used as a
model for understanding Olympia’s urban trees and their effective role in stormwater
management.

2

Literature Review
1.1 Green Infrastructure vs Grey Infrastructure
1.1.1 Definitions
Green infrastructure (GI) is an interconnected system of green space, waterways, and
other natural areas that maintain natural environmental functions while simultaneously providing
socioeconomic benefits that grey infrastructure cannot provide (see Sec. 1.5) (Benedict &
McMahon, 2002; Denchak, 2022; Seiwert and Rößler, 2018). The components of GI consist of a
wide range of natural elements, restored ecosystems, and landscape features such as trees,
shrubs, grasses, parks, ponds, wetlands and other ecological elements that provide nature-based
solutions for urban communities (Benedict & McMahon, 2002). GI represents an ecological form
of climate change resilience by combining engineering techniques and nature’s mechanisms,
mimicking the natural environment in urban communities (Beatly, 2012; Benedict et al., 2012;
Choi et al., 2021).
Despite the co-benefits GI offers, it cannot replace grey infrastructure entirely, the
conventional flood prevention system consisting of pipes, gutters, levees, and tunnels, to divert
stormwater away from homes and into treatment facilities and then into our local waterways
(Hoang and Fenner, 2014; Zhou, 2014). Grey infrastructure will always be a requirement for
hydraulic control, water quality and transportation of water aways from built structures (US
EPA, 2022; Water Portal, 2016).
Planners and communities have historically used grey infrastructure (US EPA, 2022; Soz
et al., 2016). With rapid urbanization and increased intense flooding, grey infrastructure can
break down and become less efficient, especially with the aging of grey infrastructure in many

3

areas (US EPA, 2022; Xu et al., 2019), and its consistent need for repairs (Hoang and Fenner,
2015; William et al., 2017).
For instance, water mains in New York City have an average age of 66 years and have
become more fragile over time. They also share underground space with power lines, stream
pipes, and other critical infrastructure. In 2020, several water main breaks occurred in the first
two months, warning of the city’s inadequate and aging infrastructure, on which the city spends
nearly $400 million a year to repair (Barron, 2020).
Similarly, local sewer systems also have combined drainage and wastewater
management. Seattle, WA has three types of sewer systems: combined, separated, and partially
separated, with separated being the least common. Combined sewer systems date back 70 to 100
years. Combined sewers transport wastewater from homes and businesses along with stormwater
runoff from impervious surfaces. These sewer pipes transport both wastewater and stormwater to
treatment plants. When too much water enters the pipes, wastewater can overflow into local
waterways or inundate conveyance systems, exacerbating floods known as combined sewer
overflows. While separate sewer systems may transport wastewater and stormwater in different
pipes, only 27% of the wastewater in Seattle gets separated, meaning there are two separate
systems for stormwater and sewage. In comparison, about 40% of Seattle’s sewer system gets
partially separated (Blackwell et al., 2012; Seattle Public Utilities, 2020).
The inclusion of GI elements can improve water quality by allowing natural filtration
using plants and soils, can alleviate stress and pressure on pipes and prevent system overflows by
retaining water that might otherwise drain into water and sewer systems. Considering the
projected climate change-related hazards of frequent and intense rainstorms, GI and grey
infrastructure should be used together to maximize each of their benefits (Dumuzere et al., 2014;

4

Xu et al., 2019). However, like conveyance systems, extreme rainstorm events can put stress on
GI especially if they are not properly planned or overdesigned (Tu et al., 2020). Both GI and
grey infrastructure can complement each other to reduce inundation of both types of stormwater
systems (Water Portal, 2016).

1.2 Urbanization Impacts on Stormwater
1.2.1 More Development, More Impervious Surfaces
Urban growth has accelerated globally over recent decades, with about 55% of the
world’s population living in urban areas, a number projected to increase to 70% by 2050. That is
nearly 2.5 billion more people living in urban areas than today (Nor et al., 2017; United Nations,
2018). With rapid urbanization comes an increase in total impervious areas, such as parking lots,
roadways, rooftops, and any type of human-made hard surface (US EPA, 2022). The Puget
Sound area, for example, has 359,500 acres (560 square miles) of impervious surface. That
equals more than 272,300 football fields worth of asphalt and concrete (The Nature
Conservatory, n.d.). With nearly 80,000 new people moving here annually, that number will
likely increase.
Additionally, cities in the United States have a significant ecological footprint and exhibit
unsustainable land use, but have historically given little consideration to ecological restraints
(Beatly, 2013; Chen et al., 2019; Monteiro et al., 2020). The United States relies on automobiles;
because of car-centric land use planning (Simek, 2021) most Americans favor more and larger
shopping malls, and larger single-family homes with accompanying larger roofs (Frazer, 2005)
and bigger driveways to accommodate three car garages. While impervious surfaces have existed
for a while, according to a nationwide road census, 93% of America's roads were unpaved in
5

1903 (Arnold Jr. & Gibbons, 2007). This massive transformation of American cities was
influenced by the preference of automobiles over train services in the early mid-century because
it gave people more mobility and personal freedom. As a result, decisions on urban design were
solely centered around car-centric infrastructure through the expansion of highways (Arnold Jr.
& Gibbons, 2007; Simek, 2021). Additionally, the adoption of automobiles led to the growth of
suburbia which typically had, and still has, poorly connected street networks (Ewing et al.,
2002). Since then, our preference and dependence on automobiles has increased the amount of
impervious surface area (Arnold Jr. & Gibbons, 2007).

1.2.2 Implications of Less Greenspace
Land use changes as a result of urban growth. Impervious surfaces are ubiquitous in
urban environments, altering natural hydrological processes. Compared to the natural
environment, urban environments limit stormwater absorption, increasing runoff volume and
pollutant loads into our local waterways (Sohn et al., 2020).
Many studies demonstrate how spatial patterns of land use effect urban flooding (Frazer,
2005; Hornet et al., 2022; Sohn et al., 2020; US EPA, 2013; Wendling, 2022). When
precipitation falls over land, it takes various routes. Some of it evaporates, returning into the
atmosphere, some infiltrates into the soil, and the rest becomes surface water, reaching different
bodies of water. Greater impervious surface areas alter the volume of water that permeates into
the soil, resulting in more flooding, as shown in Figure 1 (City of Olympia, 2018; Ebrahimian et
al., 2019; McCarthy, 2016).
Additionally, when rainwater washes over impervious surfaces, it collects harmful
pollutants that can often become very concentrated (e.g. nutrients, chemicals, oils, etc.),
6

ultimately carrying them into our local waterways, degrading water quality and marine
ecosystems (Chen et al., 2019; US EPA, 2022). For example, stormwater runoff is responsible
for 75% of the toxic chemicals that enter Puget Sound, emphasizing the fact that impervious
surfaces are associated with urban-environmental issues (The Nature Conservancy, n.d.).
Besides flooding and stormwater runoff, less green space results in urban heat islands
(UHI), wildlife habitat fragmentation, poor air and water quality, and negative self-reported
moods in urban neighborhoods (See Sec. 1.5) (Berland et al., 2017; Hoang and Fenner, 2014;
McFarland et al., 2019). In other words, without the consideration of green spaces, rapid
urbanization can lead to multiple socio-ecological consequences (Hamada et al., 2013; Piracha
and Chaudbury, 2022).

7

Figure 1
Impervious Surfaces Impacts on Runoff and Infiltration

Note. Compares the water cycle between low-density (more permeable surfaces) and highdensity (more impermeable surfaces) areas. In highly dense urban communities, runoff is more
than 5x greater than in natural environments. Source: Dept. of Energy and Environment,
Washington D.C.

Olympia, Washington, for instance, can be characterized as a moderately sized town,
with a rapidly growing population (World Population Review, 2022) where land use is
continuously changing with development (See Figure 2a-b). On top of that, the city has an
impervious surface area that exceeds 3,000 acres. In a typical year, this can result in four billion
gallons of runoff (City of Olympia Storm and Surface Water Utility, n.d.). Nearly 12,622 acres
of Olympia generate stormwater that eventually gets dumped into South Puget Sound, mainly
Budd Inlet (City of Olympia, 2018). Budd Inlet currently does not meet water quality standards
for dissolved oxygen (WA Dept. of Ecology, n.d).

8

Figure 2a-b
Landuse Change Olympia (1984-2020)

Note. Shows the City of Olympia 1984 (top) and 2020 (bottom) and the changes in landscape
due to development. Pictures are zoomed out due to pixelation and low photo quality on Google
Earth. Source: Google Earth Timelapse.
9

1.3.3 Different Ways Trees Control Stormwater Pollution
As opposed to impervious surfaces and the built environment which cause flooding and
runoff, trees contribute to the water cycle in many ways, controlling polluted stormwater and
providing water quality benefits to urban communities and marine ecosystems. There are several
ways healthy urban trees contribute to stormwater management and water quality protection:
a. Interception: The quantity of rain that is captured by a canopy and then evaporates is
known as canopy interception (Yan et al., 2020). When rain falls, water is temporarily
stored on the tree’s branches and leaves, preventing the majority of rain droplets from
hitting the ground. This helps in reducing peak flows, delaying the onset of floods caused
by rainstorms (US EPA, 2013).
b. Transpiration and Evapotranspiration: Transpiration is the term for the water movement
that occurs when trees and other vegetation absorb water through their roots and release it
through their leaves (See Figure 3). Water also evaporates from the leaves from
interception catch and other surfaces, which in return cools the surrounding air
temperature. Evapotranspiration is the collective name for these processes (Huang et al.,
2017; Thom et al., 2020; Yang et al., 2019).
c. Infiltration: Trees and other plants play a critical role in groundwater infiltration. Root
growth can help increase infiltration capacity rates, reducing landscape runoff (Tree
Canopy BMP, n.d.). The amount of infiltration is crucial because it controls both the
amount of stormwater that enters the soil and the absorption of nutrients and pollutants
that are filtrated before it enters the water table (Kirkham, 2014).

10

d. Phytoremediation: A term that refers to plants’ ability to sequester and break down
contaminants from the soil through their root systems (US EPA, 2013). In order to
accumulate heavy metals and control their bioavailability, plant roots play a vital role in
the soil environment, creating rhizosphere micro-organisms that help to remediate soil
contamination, maintaining and balancing soil health. (Yan et al., 2020).

Figure 3
Ways Healthy Urban Trees Treat Stormwater

Note. Visualizes the different ways trees prevent water pollution associated with their different
terms. Source: US Environmental Protection Agency (2013).

11

1.3 Climate Change Projections in Western Washington
1.3.1 General Climate in Western Washington
The Northwest region has a greatly diverse climate, with substantial spatial variations,
primarily due to interactions with the vast atmospheric circulation and the Coastal and Cascade
Mountain ranges (Kunkel et al., 2022; UW Climate Impacts Group, 2009). Western Washington
tends to be humid, mild, and temperate due to the Pacific Ocean providing moisture and frequent
precipitation. Most of Washington’s rain occurs during the winter, and the Cascades can receive
up to 400 inches of snow annually. Winter seasons rely heavily on mountain snowpack
accumulation because it provides an essential water source during the summer months (Frankson
et al., 2022). But warmer winter temperatures combined with heavy precipitation may reduce
Cascade snowpack.

1.3.2 Future Changes in Extreme Precipitation and Flooding
Climate change is likely to alter hydrological processes in urban areas, exacerbating the
severity and frequency of flooding and precipitation events (Tabari, 2020). Winters won’t always
yield high snow depths because warmer winters will become more common, causing shifts in
winter precipitation patterns from snow to rain (Global Change, 2009). Increased winter rainfall,
as opposed to snowfall, won’t be stored in our region’s mountaintops resulting in more winter
flooding, impacting urban communities (Frankson et al., 2022). Although heavier rainfall does
not always lead to floods, it can increase their potential. Moderate precipitation events can still
cause frequent flooding in urban areas where there is more impervious surface area, thus
contributing to property and environmental damages (Denchak, 2019). Pollution from runoff is

12

inevitable because impervious surfaces are everywhere in developed land (O’Driscoll et al.,
2010).
Additionally, across most of the globe, flood intensity will be expected to increase.
However, there could be considerable uncertainty in some locations. Climate characteristics have
an impact on uncertainty in changes to extreme precipitation. While semi-humid and semi-arid
regions show a lower percentage of land area with increasing flood intensity, accounting for
68.7% and 63.5%, respectively, humid regions show an increase in flood intensity on about 76%
of the land area (Tabari, 2020). In Western Washington, the daily variation in relative humidity
ranges from 85% at 4:00 am to 47% at 4:00 pm in July and about 87% at 4:00 am to 78% at 4:00
pm in January (NOAA NCDC, n.d.). That being said, Western Washington experiences
moderate-high humidity, especially during the winter, which explains the frequent winter
rainstorms. Although uncommon in Western Washington, hot temperatures and humidity can
also cause heavy rain and thunderstorms which can lead to flash floods. These events are also
likely to become more common as climate change progresses (Stalter, 2018).

1.4 Urban Ecosystem Services and Benefits
GI provides an interconnected network between ecosystems and humans, highlighting the
multifaceted benefits that can simultaneously meet multiple socio-ecological needs and interests
(Coutts and Hahn, 2015; Okpoko, 2020). Although GI is mostly recognized and utilized for
stormwater management in the United States (Choi et al., 2021), its purpose has more use and
benefits. These benefits include but are not limited to:

13

1.4.1 Ecological Benefits
a. Enhanced Biodiversity and Ecosystems
The anticipated rate of climate change, combined with habitat and greenspace
fragmentation caused by increasing urbanization, has placed numerous species at risk.
Additionally, rapid development causes migration barriers and will likely inhibit many species
from migrating to more suitable habitats (Chambers and Pellant, 2008).

GI helps provide natural habitats and connectivity for urban wildlife and ecosystems
(Lafortezza et al., 2013). Depending on vegetation and land cover types, such as urban trees, GI
may promote species richness and support urban wildlife when properly maintained (FrancineFelappi et al., 2020). Much epidemiological research shows higher bird species richness or
animal diversity in urban parks is associated with positive mental well-being among urban
dwellers (Methorst et al., 2020; Wolf et al., 2020). GI also restores, modifies, and maintains
natural ecosystems while simultaneously addressing societal challenges among urban
communities (Benedict and McMahon, 2002).
b. Water Quality
Stormwater runoff is a significant contributor to water pollution. When rain falls on
impervious surfaces, stormwater collects various contaminants, heavy metals, and nutrients from
anthropogenic activity (see Table 1) and then discharged into nearby waterways rather than
infiltrating into the soil (Chen et al., 2019; Madsen and Figdor, 2007). Excess nutrients, for
example, cause fish kills, algae blooms, and the spread of invasive non-native plants (Hostetler et
al., 2011; Morton, 2017). Stormwater contaminants are toxic to plants and animals, especially

14

those symbolically and culturally important to the PNW including salmon, orcas, oysters,
geoducks, eelgrass beds, and kelp forests (WA DNR, 2020).
Table 1
Common Stormwater Pollutants

Note. In-depth description and details of common pollutants in stormwater and their sources.
Retrieved from: McFarland et al., 2019.
GI improves water quality, enhancing local aquatic ecosystems (Chambers and Pellant,
2008; Xu et al., 2019). For instance, pollutants like heavy metals, 6PPD-quinone from tires,
motor oil, fertilizers, and many more collected from stormwater runoff in urban areas, are
captured and filtered out by soil and permeable surfaces. By incorporating more permeable

15

surfaces, healthy GI prevents stormwater pollutants and heavy metals from entering waterways
(Dixon & Goh, n.d.; McFarland et al., 2019) through infiltration and phytoremediation.
c. Air Quality
Many cities suffer from air pollution because of poor planning and expanding urban
environments (Piracha and Chaudhary, 2022). In the United States, the most common source of
air pollution comes from mobile sources, such as cars, planes, buses, and trains (US NPS, 2018).
Most US cities lack adequate public transportation so that residents rely on their cars as their
main mode of transportation, causing carbon emissions and air pollution (Simek, 2021). Air
pollution can be exacerbated by urban heat islands and a lack of green space, causing impacts on
human health and urban ecosystems (EHN, 2021; Jesdale et al., 2021).

GI alleviates air pollution through carbon sequestration. Vegetation directly absorbs
gaseous air pollution like carbon dioxide (CO2) from the atmosphere through leaves’ stomata
(Nowak et el., 2013; Demuzere et al., 2014). Trees also act as a buffer against air pollution by
removing ozone (O3), particulate matter (PM), Nitrogen dioxide (NO2), Sulphur dioxide (SO2),
and carbon monoxide (CO) from the atmosphere (James et al., 2015). For example, in the United
States, the amount of pollution sequestered by urban trees differs across major metropolitan
areas, with an average of 711,000 tonnes of pollution removed per year. (Nowak et al., 2006;
Nowak et al., 2013). Although the amounts of each pollutant sequestered vary, to put it into
perspective, 1 ton of CO equals 102 gallons of gasoline consumed and 2,252 miles driven by an
average gasoline-powered passenger vehicle (US EPA, 2022). This equals 72,420,000 gallons
and 1,598,920,000 miles of CO2 omitted from air pollution by urban trees.

16

1.4.2 Social Benefits
a. Urban Heat Islands (UHI)
Concrete, buildings, and other impervious surfaces from cities absorb, retain, and re-emit
more heat than natural vegetation, causing urban heat islands (UHI) (Berland et al., 2017;
O’Driscoll et al., 2010;). For example, daytime temperatures in cities are about 1-7 °F higher
than in rural areas, and nighttime temperatures are about 2-5 °F higher (US EPA, 2022). Summer
high temperatures in cities are becoming more severe, and UHI is considered a significant
indicator, directly or indirectly, threatening human health such as heat-related illnesses (Huang et
al., 2022).
Urban trees alone provide canopy shade on a hot day, and also cool through transpiration
when surrounding air is cooled as water goes from liquid to vapor (Berland et al., 2017; Gao et
al., 2020; Kong et al., 2016;). Urban trees also influence indoor temperatures by shading
buildings and dramatically lowering the risk of indoor overheating (Pianella et al., 2020;
Salmond et al., 2016). The cooling effects of urban trees and green space on the urban landscape
ensure necessary UHI and heat-related illness prevention across urban communities (Hamada et
al., 2013).
b. Physical and Mental Health
Human health and the built environment are inextricably linked. Poor mental health
among urban dwellers has been associated with urban-environmental issues such as air and water
pollution, UHI, noise pollution, and, depending on social conditions, increased criminal activity
(Jesdale et al, 2015; Piracha and Chaudbury, 2022; van den Berg et al., 2014). Lack of GI can
put underserved communities more at risk of poor mental and physical health, compared to
wealthy neighborhoods that benefit from GI (Gruebner et al., 2017). For instance, studies in St.
17

Louis, Missouri found a correlation between violent behavior and excessive heat temperatures,
especially across underserved communities (Mares, 2013; Miles-Novelo and Anderson, 2019).
While neighborhood characteristics and socioeconomic factors, such as poverty and lack of
green space, play a role in aggressive behavior, higher temperatures can also exacerbate or cause
a range of mental health issues (PD&R, 2016; Seo, 2022).

Greenspaces, like urban trees, can alleviate negative natural and physical environmental
conditions that may contribute to poor human health. For example, living near, or in the presence
of greener environments is correlated with better self-perceived mental health (Cox et al., 2016;
Lafortezza et al., 2013; Methorst et al., 2020), such as reduced negative thoughts and betterreported moods (Turner-Skoff and Cavender, 2019). Greenspace also encourages walking and
biking while simultaneously providing critical habitat for urban ecosystems for bird and wildlife
watching, which also contribute to protective measures against self-reported negative mental
health outcomes (James et al., 2015; US EPA, 2017).

c. Equity
Low-income communities are not only disproportionately impacted by climate changerelated hazards but also lack environmental amenities and access to green space (Homet et al.,
2022; Meerow, 2019). Current evidence shows that historically redlined neighborhoods are some
of the hotter parts of the city during the summer, with less tree cover and more pavement
(Anderson, 2020; Plumer et al., 2020). Hoffman et al. (2018) conducted a spatial analysis to
study the connection between historically redlined neighborhoods and urban surface
temperatures. They explored 108 US Cities with Home Owners’ Loan Corporation (HOLC)

18

maps and discovered that 94% of the study area showed surface temperatures were, on average,
up to 2.6 degrees Celsius higher in redlined neighborhoods than in non-redlined neighborhoods.
Similarly, communities of color in urban areas tend to bear the burden of extreme heat events
and are underserved, receiving inadequate environmental services such as urban trees (Jesdale et
al., 2013).
GI provides a climate justice approach for vulnerable communities that have been
historically and continuously disregarded and underserved. As mentioned, urban trees provide
significant benefits in big cities. They offer countless environmental amenities for urban dwellers
by alleviating flooding, environmental pollution, negative self-reported mental health, and UHI
(Homet et al., 2022; Turner-Skoff and Cavender, 2019; US EPA, 2017). This will be essential in
low-income neighborhoods that face uneven distribution of greenspace and environmental
commodities (Soz et al., 2016).

1.4.3 Economic Benefits
a. Lower Energy Costs
Frequent heat waves can have significant impacts on the economy and environment
because they lead to increased energy consumption. When it's hot out, homeowners and
businesses turn on their air conditioning (AC) units and other cooling equipment to stay cool
(Lemoine, 2021). AC systems in particular consume more than 50% of total electricity demand
during heat waves, with a maximum consumption of up to 65% of total electricity demand
during peak late afternoon hours (Sharma et al., 2018). Increase electricity use on hot days can
strain electric grids, resulting in blackouts, which not only can be costly to the economy but also

19

expose millions of residents to hazardous levels of heat (Lemoine, 2021; Sharma et al., 2019;
Stone Jr. et al., 2020).

GI provides microclimate regulation of UHI and decreases the energy demand required
for air conditioning in residential homes and businesses by providing shade and shelter,
minimizing consumer costs (Blackwell et al., 2012; Lin et al., 2014). Tree canopies and forested
parks, in particular, can have an average cooling effect of about 1 degree C (33.8 degrees F) in
air temperature, but could also have a significant effect on thermal comfort, especially during
heat waves (Lee et al., 2014; Kong et al., 2016; Venter et al., 2019).

b. Prevention Loss and Disaster Risk Reduction
Grey infrastructure generally increases environmental costs by degrading the landscape
and ecosystems due to the lack of permeable surfaces (Onuma and Tsuge, 2018). Flooding, for
example, caused by heavy precipitation can cause widespread economic disruption by destroying
roads and bridges, inundating homes, businesses, pipes, and other critical infrastructure such as
transportation, and in some cases, kill or severely injure people (Madsen and Figdor, 2007).
Additionally, cleaning and remediating water systems polluted by runoff can be not only difficult
and long-term, but also expensive (Blackwell et al., 2012).

Hazard mitigation planning in terms of flooding ensures social, environmental, and
economic protection. Preventing and preparing for major storm and flooding events protects life,
habitat, and property which in return, lowers the cost of recovery (FEMA, 2018). GI, along with
grey infrastructure, helps communities become more flood-resistant by focusing efforts on urban

20

areas that remain vulnerable to floods. While some GI techniques may have high initial costs,
such as green roofs, they eventually save more money in the long term by reducing the volume
of stormwater entering conveyance systems and the rate of runoff (US EPA, 2015). “Beyond
code” (surpassing minimal building requirements) hazard mitigation has an overall benefit-cost
ratio of 4:1 (See Figure 5). This means you can save, on average, around $4 for every $1 you put
into mitigation (FEMA, 2018).

Figure 4
Hazard Mitigation Cost-Benefit Ratio

Note. Riverine flood mitigation grants and beyond code projects save more money than they
cost. Federally funded riverine flood mitigation projects save significantly more money than they
cost (with a 7x return on investment). Occupant safety is improved by both above-code design
and public-sector mitigation for riverine floods. Figure source: FEMA, 2018.
c. Public and Environmental Health
Runoff not only causes water uninhabitable for aquatic habitats but also threatens human
health. Inappropriately managed water causes serious illnesses and transmission of diseases for
people who come into contact with dirty sand or water (Hu, 2020). For example, Puget Sound
21

has a lot of recreational and water activities such as kayaking, paddle boarding, scuba diving,
fishing, and much more. However, some of the parameters of the Clean Water Act that
negatively impact Puget Sound include fecal coliform, temperature, pH, fine sediment, and
dissolved oxygen due to excess nutrients (City of Olympia, 2016). Poor water quality from
stormwater runoff, such as the elements mentioned, cause polluted beaches that can be unsafe for
recreation and marine wildlife (City of Olympia, 2016).
Environmental protection contributes to economic prosperity. For example, in 2021,
Washington’s fishing, hunting, and wildlife-watching activities contributed over $4.5 billion
each year in overall economic activity (WDFW, 2022). Without proper protection and
conservation policies for clean water, recreational opportunities are at risk, opportunities which
are important for economic growth (O’Driscoll et al., 2010). GI also prevents people from
becoming ill in contaminated groundwater and recreational waters (Blackwell et al., 2012).
Besides alleviating poor air quality and urban heat islands, GI protects communities built on
shorelines and watersheds, preventing pollution from system overflows during heavy rainstorms
(Hu, 2020).

1.5 Significance of Urban Trees
We need more GI stormwater management in urban areas as cities and populations grow.
GI serves a multifunctionality purpose providing many socio-ecological and economic benefits
and services that are not limited stormwater management (Monteiro et al., 2020). Although grey
infrastructure does have practical and effective hydrological functions, it does not have the same
environmental advantages (Szoenyi and Svensson, 2019). The environmental, social, and
economic impacts of switching to GI won’t compare to the consequences of stormwater water
22

runoff from built environments, but the implementation of GI does not result in eliminating grey
infrastructure. GI can help reduce the need to expand and rely on conventional stormwater
management as both practices are beneficially used together (Fung et al., 2016). In this study, I
will look at the role of urban trees in Olympia, Washington for stormwater management,
specifically analyzing the value of potential pollutant removal efficiency, while also looking at
the value of Yauger Park in water treatment cost reductions.

23

Methods
I obtained data that allowed me to assess the economic advantages of Olympia's urban
forests using a number of different methods.
First, I adopted a model outlined in Snoqualmie’s 2020 Natural Infrastructure
Assessment done by the project team, The Keystone Concept, Equilibrium Economics, and
Ecosystem Sciences. Snoqualmie’s Natural Infrastructure Assessment focused on the economic
value of forest ecosystem services and stormwater management benefits provided by the city’s
urban forests and how those forests will continue to provide if continuously maintained and well
managed. Considering Olympia, Washington lacks data on urban trees and their role in
stormwater management, conducting an analysis like the one outlined in the Natural
Infrastructure Assessment allowed me to understand the role of Olympia’s urban forests. This
assessment was chosen to draw implications for Olympia’s urban forestry for five main reasons:
1. The publication year: Recent -- conducted within the last year.
2. The location of the study: Both in Western Washington.
3. Climate change adaption and mitigation efforts covered: Focus on stormwater
management, reducing runoff and erosion.
4. The type of green infrastructure: Urban trees and urban forestry.
5. The quantitative information on the co-benefits related to climate benefits.

To demonstrate the benefits of retained forest land within the city for stormwater and
water quality, the Snoqualmie project team focused on three different city-owned forest cover
classifications. These forested lands are outlined in three different case studies: contiguous to the
Snoqualmie River and its tributaries, within Snoqualmie Ridge, and within City-owned right-ofways (ROW). The data I chose to analyze for Olympia’s urban trees was based on the case
24

studies and framed around stormwater nutrients sequestered by urban trees and the value these
forests provide to the city in terms of water quality. That included:
1. The effectiveness of urban trees and forests in removing and infiltration pollutants such
as phosphorus and nitrogen that are common in stormwater.
2. The economic value of urban trees and forests in providing water quality, such as treating
stormwater pollution

Local projections of the nutrients and pollutants removed from stormwater by an acre of
forests were combined with the marginal cost of grey infrastructure water treatment to develop
the annual dollar value per acre of water filtration provided by Snoqualmie's forests: Compounds
Filtered from Water of Urban Forests (kg/acre/yr) x Marginal Cost of Conventional Filtration
Infrastructure ($/kg).

!"#$"%&' )*+,-.-' (01)

!4$*,4+ !"8, ($)

x
= Total value (acre/year) of water quality
3.-4 4&&%4++5 (46.-/5.) !"#$"%&' )*+,-.-' (01)
benefit of natural infrastructure.
How the data in the Snoqualmie report had been processed was kindly provided by
reaching out to the project team, Lance Davisson of the Keystone Concept, and Zac Christian of
Equilibrium Economics. According to the project team, a transfer of benefits and values from
previous studies was used to analyze stormwater benefits, including the amount of nitrogen and
phosphorus sequestered and the separate market values for those nutrients. Local estimates of
compounds filtered from stormwater of urban forests (kg/acre), for instance, were used from a
2013 study by Hill et al., using a benefit transfer of values approach. The authors looked at the
benefits forests nearby headwater streams and catchments in Washington State provide to water
25

quality. Data on catchment attributes related to the reduction of nitrogen, phosphorus, and total
suspended solids were collected as part of the EPA's National Rivers and Streams Assessment.
A transfer of values was also used for the marginal cost of filtration infrastructure,
provided in the report. One of the selected market values came from the US EPA's 2009
publication “Water Quality Trading Toolkit for Permit Writers.” These values were selected
based on the most current and relevant market values. Relevance was selected based on nonagricultural costs for nutrient reduction to prevent overestimating market values (Christin,
Davisson, Maguire, & Anderson, 2020).
Local estimates of acres of urban trees were obtained by submitting a general Public
Records Request through Olympia’s Request Center online, asking “How many acres of urban
trees are within the city of Olympia?” Using similar data processes and values from the
Snoqualmie Assessment, I calculated the annual water quality benefits for Olympia’s urban trees.
Data from the report was used to estimate the benefits and assess the implications of the potential
economic benefits of Olympia’s urban forests for water quality and stormwater management.
The Green Values Stormwater Management calculator estimated the potential cost
benefits for using GI to mitigate urban flooding. Each benefit (energy cost reduction, CO2
sequestration, air quality, real estate value, water quality, etc.) was represented in table, broken
down by who receives those benefits (community or homeowner) as well as the associated
annual value per unit. Specific benefits were chosen based on the relevance of the type of GI and
its association with water quality and stormwater management. These values were used to assess
the water quality treatment of Olympia’s Yauger Park stormwater retention pond.
Benefit transfer values are a more cost-effective alternative to analyzing and drawing
conclusions from other studies than conducting primary research at a site-specific location,

26

which can be costly. By applying values from earlier research to current research at comparable
location sites, it allows people to make quick quantitative, detailed estimates about the benefits
and values of their research area (Plummer, 2009).

27

Results and Discussion
Using the benefit transfer of values from the study by Hill et al., nitrogen and phosphorus
sequestration in the Western Mountain ecoregion were estimated at 33.6 kg/ha and 1.4 kg/ha,
respectively. I converted the units to kg/acre to match the units represented in the Snoqualmie
report, which came out to be 13.6 kg/acre for nitrogen and 0.54 kg/acre for phosphorus.
A transfer of values was also used for the marginal cost of filtration infrastructure,
provided in the report. Table 2 shows the annual high and low nutrient market values used for
nitrogen and phosphorus provided in US EPA's 2009 Toolkit. I used these values to assess the
annual dollar per acre of water filtration.
According to Olympia’s Public Works Department, as of 2013, there were about 1,727
acres of conifer trees and 1,343 acres of deciduous trees, for a total of 3,070 acres of urban trees.
There isn’t any new or updated data on urban tree acreage, according to the city of Olympia.
Putting these values into the water quality benefits equation, I determined the estimated
annual dollar value of water filtration provided by Olympia’s urban trees as shown in Table 3.
The total was rounded to the nearest dollar.

28

Table 2
Annual Value of Nutrient Reduction per Acre
Nutrient

Amount
Sequestered
(kg/acre/year)

Nutrient Market Value
($/kg)

Value of Nutrient
Reduction ($/acre/year)

Low

High

Low

High

Nitrogen

13.6

$3.13

$5.88

$42.56

$80

Phosphorus

0.6

$2.61

$57.66

$1.56

$34.6

TOTAL

$44

$115

Note. Shows the high and low values of nitrogen and phosphorus reduction ($/kg/year) in
stormwater by Olympia’s urban forests using the marginal value of nutrient reduction multiplied
by the amount sequestered each year.
Table 3
Total Annual Value of Nutrient Reduction for Olympia’s Forests
Value of Nutrient
Reduction ($/acre/year)

Value of Nutrient
Reduction ($/year)

Low

Low

High

$76,195

$197,914

Tree/Forest
Type

Acres

High

Coniferous

1727

Deciduous

1343

$59,253

$153,908

Total

3070

$135,448

$351,822

$44

$115

Note. The annual value of nutrient reduction for the entire forest was calculated using the value
of nutrients per acre per year from table 2, multiplied by the area of each forest type.

29

By applying the annual cost per acre for the water filtration that forests provide, I found
the annual value of nutrient reductions for all of Olympia’s urban trees. Assuming these trees are
mature and still remain, I conclude Olympia’s urban trees generate $135,448 - $351,822 annually
in water quality benefits across the entire city. In contrast, the city of Snoqualmie’s annual value
for improved water quality of urban forests ranges from $117,780 to $301,880 (Christin,
Davisson, Maguire, & Anderson, 2020). While Olympia’s water quality benefit values are
higher, it’s important to note Snoqualmie is a smaller city and therefore has less urban tree
coverage.

Yauger Park Case Study

Figure 5
Olympia’s Storm and Surface Water Utility

30

Using the Green Values Calculator Methodology, Green Values show estimates of the
savings on energy costs the home or building owner will receive, community benefits, and
estimated real estate value as a percentage of the current value represented in Table 4 below.

Table 4
Homeowner and Community Benefits of Urban Trees
Benefit

Annual
Value

Unit

$36

Per Tree

$0.18

Per Tree

Carbon Sequestration from Trees $0.12

Per Tree

Compensatory Value of Trees

Per Tree

Owner Benefits
Reduced Energy Use from Trees
Community Benefits
Reduced Air Pollutants from
Trees

$275

Water Treatment Cost Reduction $29.94

Per acre feet

Groundwater Replenishment

Per acre feet

$86.42

Note. Annual value of urban tree benefits. Source: Green Values Stormwater Calculator, n.d.
Yauger Park in Olympia is critical to the city’s stormwater management system. In 1977,
the park incorporated a stormwater facility consisting of 29-acre retention pond when the Capitol
Mall was built. Before the city built the park’s stormwater facility, rainstorms caused nearby
roads to flood. By design, Yauger Park is intended to flood, serving as a giant stormwater
retention pond during heavy rainstorms to reduce runoff. The pond can hold up to nearly 27
million gallons of stormwater when full, preventing flooding from nearby roadways, homes, and
commercial development (Stream Team, 2021). The retained and excess stormwater slowly
31

drains to Black Lake Meadows Reserve through a combination of conveyance pipes and wetland
channels where it is eventually released into Budd Inlet (Stream Team, 2021). Using Yauger
Park as an example, I was able to calculate the total water treatment cost reduction of stormwater
of the retention pond represented in Table 6. I also converted acre-feet into U.S. gallons to match
the unit of Yauger Park’s retention volume capacity as shown in Table 5.
Table 5
Reduction Rate Conversion
Stormwater Benefit

Reduction Rate

Water Treatment Cost $/Acre Foot
Reduction
1

$/gal
325,852

Note. A common unit of measurement in hydrology is the acre foot, which measures the volume
of one foot of water on an acre of land. This equals to about 325,852 U.S. gallons.
Table 6
Total Water Treatment Cost Reduction of Yauger Park
Amount of Stormwater
Detained (U.S. Gal)

Reduction Rate
(Acre Foot)

Value/Unit (Acre
Foot)

Total Reduction
Cost Rate

27 million

82.85

$29.94

$2,481

Note. Yauger Park detains up to 27 million gallons, which is equivalent to 82.85 acre-feet. Using
the cost reduction value of $29.95/acre-foot, the cost reduction rate of Yauger Park is estimated
to be around $2,480.

Based on the Green Values calculator, the total estimated cost of water treatment
reduction for Yauger Park is $2,481. On average, Olympia, WA receives 57.7 inches of
32

precipitation annually with January, November, and December being the wettest months out of
the year (Weather and Climate, n.d.). Based on this, I was able to estimate the retention pond
floods, on average, about three months out of the year. As a result, Yauger Park's retention pond
will save about $223,241 annually on water treatment expenses, assuming it rains enough for the
pond to reach its maximum 27 million gallons.

Economic Footprint

With these estimates, the values of Olympia’s stormwater benefits for urban trees and
Yauger Park alone equals to about $358,696 - $575,069 annually as shown in Table 7. This does
not include other types of green infrastructure and vegetation in Olympia, such as grass cover,
urban parks, rain gardens, porous pavement, etc., which undeniably contribute to the overall
water quality values. It is important to note that these two values are not related and are two
different benefit transfer methods. The annual water quality for urban trees takes in account the
nutrients sequestered from stormwater while the water treatment of Yauger Park contributes to
cost reduction of avoided runoff. Regardless, both values contribute to stormwater quality and
mitigation for the city of Olympia.

33

Table 7
Annual Stormwater Benefits for Olympia’s Urban Trees and Yauger Park
Annual Water Quality
Benefits of Urban Trees

Annual Water Treatment
Cost Reductions of Yauger
Park

Total

Low

High

$223,247

Low

High

$135,448

$351,822

$358,696

$575,069

Note. The combined annual values of stormwater quality and benefits from urban trees and
Yauger Park. Totals are rounded to the nearest dollar.
In contrast, new and retrofitted grey infrastructure projects typically have large costs for
planning, design, maintenance, and construction (EFC, 2019). Currently, more than 100
stormwater outfalls connect to the downtown drainage system with Budd Inlet and Capitol Lake.
According to Olympia’s Capital Facilities Plan, the total cost estimate to improve water quality
and manageability in Olympia’s surface water through projects that treat contaminated
stormwater water is around $3,000,000. Projects under the Capital Facilities Plan cover periods
of five years (2020-2025) and this cost was calculated on a per-year expenditure. Overall, these
water quality values provided by Olympia’s urban trees highlight the substantial cost savings
natural infrastructure contributes to water quality and stormwater management. These cost
savings will also continue to provide water quality benefits if they are continued to be protected
and well taken care of.

34

Benefits
Using Snoqualmie’s Natural Infrastructure Assessment to apply data to Olympia’s urban
forests and trees not only highlights the benefits the role of urban trees in Olympia has for
stormwater management but also allows for more research into the unexplored possibilities of
Olympia’s natural infrastructure. Snoqualmie also represents a relatively small town that has
experienced rapid development due to population growth over the past several decades, similar
to Olympia. On top of that, as the effects of climate change are predicted to worsen, shifting
investment priorities and policy toward the protection and restoration of ecological resources can
offer a more stable and sustainable basis for future economic and societal progress in Olympia.
The estimates from the analysis presented here can also help the city regulate, protect, and plant
more trees or build more green infrastructure as investments in protecting and implementing
more tree planting provisions as well as other green infrastructure types generate positive
economic and social outcomes.
Additionally, attempting to quantify the value of urban trees and the benefits they provide
for stormwater management allows planners and policymakers to compare the capital costs and
value of conventional infrastructure and manage natural resources more sustainably (Blackwell
et al., 2012). This can have an impact on current and future city planning budgets for stormwater
and wastewater. A dollar is a unit of value that is universally recognized, makes it easier for
people to understand not only their economic value but also their relational value and ecosystem
services they provide for urban communities. In exchange, monetary values on environmental
services can influence our behaviors toward the environment, such as putting more effort into
protecting natural resources. In terms of costs and advantages, it can also be helpful prioritizing
between gray infrastructure and green infrastructure (Baptista et al., 2020).
35

Limitations
There are inherent limitations and disadvantages to any study, especially when the
subject includes complex natural systems and transfer values. Although benefit transfer methods
have many advantages, they also have their downsides.
These cost-benefit estimates may not be accurate. Reporting of existing studies may be
inadequate to draw needed implications and conclusions on Olympia forests and current
stormwater quality conditions.
Hill et al.'s 2013 study used data and literature from 2000-2012, therefore unit values of
estimates were outdated by the time the article was published. Additionally, although the
Western Mountains ecoregion in the study included western Washington, it also included areas
such as Montana, Utah, New Mexico, Colorado, and California. This is likely due to similar tree
species composition, but sequestration rates may not represent Washington as a whole
considering climate characteristics and location can affect forests’ ability to sequester nutrients.
This is also true for the health of the forest, growth rate, size and maturity, and demographic
structure. Averaging nitrogen and phosphorus sequestration rates for different states while taking
these different factors into consideration may not be illustrative of the PNW or western
Washington in general.
Local estimates of urban trees within Olympia were also outdated. Considering the city of
Olympia has become increasingly urban, has made plans to build more green infrastructure for
stormwater management (US EPA, 2015), and on the surface has pro-environmental attitudes,
it’s unknown whether the acres of forest have increased or decreased. That being said, given the
dire need for more green infrastructure due to climate change and a growing population, the City

36

of Olympia should keep this data updated. Additionally, data related to forest types, such as
private vs. public, right of ways, species of trees, etc., were also limited.
Lastly, nutrients in the study were also limited to nitrogen and phosphorus. These
nutrients are not only common, extensively researched, and are typically filtered by grey
infrastructure, but were also limited in Snoqualmie’s assessment. Although nitrogen is the
primary contributor to hypoxia, which causes algae blooms and extreme stress on aquatic
ecosystems (City of Olympia Public Works Water Resources, 2010; Hostetler et al., 2011), other
pollutants in stormwater, such as tire particles (6PPD-Quinone), motor oil, and other particles,
were not included in the analysis. Knowing how much of these pollutants can be avoided from
runoff by Olympia’s urban trees is beneficial considering these pollutants are ubiquitous in urban
environments and cause degradation to water quality and marine ecosystems (McFarland et al.,
2019).

37

Conclusion
Rapid development, along with climate change, poses serious threats to urban
communities. As our cities grow, the urban trees and vegetation are replaced with impervious
surfaces. Roads and other components of the built environment pollute water sources, such as
Budd Inlet and Capitol Lake in Olympia, WA. In contrast, urban trees provide ecosystem
services that are the foundation of economic prosperity and environmental health, mitigating
ecological calamities associated with growing cities specifically stormwater management and
water quality benefits. Healthy urban trees and other types of green infrastructure (GI) generate
less runoff (reduces the amount of stormwater), allow infiltration (recharges groundwater), and
minimize pollutants (decreases surface water contact), that flow into local waterways.
In this study, I found that Olympia’s urban trees provide an estimated $358,695 $575,068 annually towards water quality and stormwater quality benefits. Olympia still lacks
adequate data relating to GI and its role in stormwater management with outdated data on urban
tree acreage. These limitations highlight the need for more research on the stormwater systems
associated with green infrastructure in Olympia as well as keeping tree inventory data updated.
Despite the limitations to these estimated values, nature provides many services and
benefits for human survival. Urban trees and forests provide significant stormwater services,
enhancing water quality, while simultaneously providing other benefits such as economic
prosperity and healthy urban environments. However, not everyone acknowledges the services
and economic importance nature provides. As a result, some people may overlook the
interconnectedness of life on Earth and unintentionally exploit their natural resources (Bilmes,
2021). When the value of natural systems is acknowledged, it becomes evident that conservation
and restoration projects can generate valuable socio-economic and environmental benefits in
38

return. Unlike built infrastructure, natural structures don't lose value over time. Protecting and
preserving natural systems from deterioration, development, unsustainable extraction, and other
effects is essential if they are to remain effective and sustainable. If Olympia’s forests are
properly managed and continue to be healthy, the city's residents will receive these economic
benefits each year and indefinitely. Thus, GI provisions are an essential component in climate
change mitigation and resilience in urban communities.

39

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The Evergreen State College Masters Theses: Environmental Studies

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