Increased flood resilience can reduce damage to property, infrastructure, and environmental amenities. It also reduces adverse health risks associated with exposure to flooding and basement backups, avoids emergency response and cleanup costs, and limits the economic impacts of street or business closures from flooding. The benefit of projects that reduce flood risk can be calculated based on the costs of these avoided impacts.

Federal agencies and others have developed well-established methods and tools for assessing avoided flood damages. These approaches are generally applicable to larger-scale riverine and coastal flooding and involve modeling to estimate the flood damage costs that will be avoided over the life of a project. Data on the depth and extent of flooding under various storm return intervals (e.g., 10-year, 100-year storm events) and information on the characteristics of the affected area (e.g., information on structures, businesses, land uses, population impacted) are necessary to run these models.

The benefits of projects that address localized or nuisance flooding can be more difficult to estimate. Smaller storm events may cause little flood-related damage without the project but can inconvenience residents and community members by causing unsafe conditions, road closures, and/or basement backups. Analysts have quantified the benefits of reductions in localized flooding based on WTP by households to avoid flood risk, avoided basement back up costs, or impacts on the value of properties affected by a flood risk reduction project. These methods require different inputs.

Another method for valuing the benefits of nature-based solutions for flood risk reduction is quantifying the avoided costs of alternative flood control options (e.g., managing flooding through gray infrastructure approaches). This method can be applied to projects that reduce larger scale flooding and flooding associated with smaller storm events.

Avoided flood damages – projects that address larger scale flooding

The benefits associated with larger-scale riverine and coastal flood risk reduction projects can also be valued based on the flood-related damages that will be avoided over the life of the project. This method is appropriate to use when comparing the project to a “no action” alternative. Depending on the extent and severity of the flooding event, avoided damages may include structural damages to buildings, loss of building contents, damages to infrastructure or critical facilities, loss of wages and profits to businesses, emergency response costs, displacement, injury or loss of life, and post-flood cleanup costs.
To calculate avoided damages, practitioners must estimate and compare flood damages with and without the project. Key steps are outlined below:

Step 1: Define and inventory the area over which flooding will be mitigated
A floodplain inventory is needed to identify the types of buildings and other assets at risk. Key data requirements include size, population, property type, property values, and structure characteristics within the management area. This does not have to involve an extensive study – the US Army Corps of Engineers (USACE) developed and maintains the National Structure Inventory (NSI), a repository of structure point data containing building-level attributes in a GIS base layer that can be used for this purpose.

Step 2: Conduct hydrologic and hydraulic modeling.
The next step is to understand how the extent and depth of flooding will change with and without the proposed flood risk mitigation measures. This can require a rainfall-runoff (hydrologic) model to route rainfall over the landscape. A hydraulic model may also be needed to understand the performance of the stormwater and wastewater system during rain events. This cannot always be done in house and municipalities often hire consultants to perform this modeling.

Step 3: Estimate damages with and without project
Depth-to-damage functions are then used to translate the depth of flooding into physical damages, given the existing stock of buildings and their classification (e.g., residential, commercial, industrial classification codes), and nonphysical damages (e.g., emergency response, displacement, flood cleanup costs). The range of storm event return periods and their expected damage amounts are used to calculate expected annual damages across all storm event types. This process accounts for the probability of occurrence of different flood events. Damage estimates can be conducted using tools developed by USACE or FEMA that provide standardized relationships for estimating flood damages and other costs of flooding.

Avoided infrastructure costs

If the baseline scenario includes an alternative project for addressing flood risk reduction (e.g., through a gray infrastructure project), the costs of the avoided project can be included as a benefit of the green infrastructure or nature-based resilience project. Costs of the avoided project should include lifecycle costs – from design, construction, to maintenance over time. Costs should be calculated for the period over which the project would have been implemented for appropriate comparison in present value terms. Consideration should be given to the expected life of the avoided project. For example, if the nature-based resilience project has an expected life of 50 years (or is being evaluated over a 50-year period), and the avoided project has a useful life of 30 years, replacement costs (or decommissioning costs as relevant) incurred at the 30-year mark should also be included as an avoided cost.

For projects intended to manage larger-scale riverine or coastal flooding, these avoided costs may be best developed based on high-level engineering cost estimates (if available). For green infrastructure projects that address localized flooding, avoided costs can include the cost of managing stormwater runoff to local standards (e.g., MS4 permit requirements) using traditional gray infrastructure. For example, R.S. Means, a widely used database for construction cost estimating, reports capital/construction costs for managing a square foot of impervious area using traditional methods (i.e., underground storage and drainage networks). In 2024 USD, this value amounts to $3.68 per square foot of impervious area managed. Multiplying the impervious area managed with the green infrastructure project/nature-based solution by the unit value avoided cost ($3.68 per square foot) yields a total avoided cost benefit. This can be supplemented by local cost data for managing stormwater runoff within the public right-of-way. In addition, this is a onetime avoided construction cost; maintenance costs should also be estimated and included in the avoided cost estimate.

Importantly, the cost for managing stormwater runoff includes costs for meeting both volume and water quality based standards. Thus, if this approach is used to estimate the benefits of projects that reduce localized flooding, water quality benefits should not be separately evaluated.

Additional methods for estimating flood risk reduction benefits of projects

The types of flooding targeted by green infrastructure also does not always result in the types of damages captured in the models described above. Economists have developed alternative approaches for valuing flood risk reduction benefits associated with these projects. For example, researchers have used stated preference surveys to estimate the willingness to pay (WTP) of households to avoid street flooding, basement flooding, or basement backups. Across studies, household WTP ranges from $50 – $88 per year.

Others have used hedonic pricing methods to investigate the effect that flood risk has on housing prices. For example, several studies have found that the value of homes within the 100-year floodplain are 2% – 8% lower than equivalent homes outside the floodplain. Another study found that on-site retention to mitigate flooding can increase property values by 2% – 5% for properties located in the flood plain.

Local planning data or knowledge of flood damages can also be used to estimate project benefits. For example, if a green infrastructure or other nature-based project is implemented to address basement backups in a neighborhood, local knowledge can inform estimates on the frequency and number of basement backups that occur each year, as well as the costs associated with clean up. This can yield an order of magnitude estimate of the damages that will be avoided by the project.

Finally, a simple way to estimate the flood risk reduction value of some nature-based practices is to rely on ecosystem service values developed by the Federal Emergency Management Agency (FEMA)  for different land use types. Using benefits transfer and existing academic studies, FEMA estimates national average values for flood and storm hazard reduction for several applicable land use types (Table 1).

Local planning documents and data can inform relatively simple calculations of flood risk reduction benefits. Additional resources include:

US Army Corps of Engineers National Structure Inventory (NSI) includes information about the location, type, and value of buildings and infrastructure.

Tools developed by the Federal Emergency Management Agency (FEMA) for estimating benefits of flood risk reduction projects: HAZUS, FAST, Benefit-Cost Analysis Toolkit, and Ecosystem Service Values.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool) is an Excel-based benefit-cost assessment tool that allows users to quantify the financial, social, and environmental benefits of green infrastructure solutions. The green infrastructure TBL Tool contains a module that allows users to estimate the avoided infrastructure costs associated with more traditional gray infrastructure projects for stormwater management, including projects that reduce flood risk and improve water quality.

Like flood risk reduction benefits, water quality improvements from green infrastructure and other nature-based resilience projects can be estimated based on the avoided costs of alternative water quality treatment options. Avoided treatment costs depend on the pollutant load reductions resulting from nature-based projects, such as pounds of nitrogen, phosphorous, or total suspended solids (TSS) removed. Unit treatment cost values (e.g., $ per pound of pollutant treated at a wastewater treatment plant) can be applied to pollutant removal estimates to determine the value of total water quality benefits. When using avoided costs to estimate the water quality benefits of nature-based solutions, care must be taken to avoid double counting with any avoided infrastructure costs calculated as a flood risk reduction benefit.

The value of water quality improvements can also be estimated based on public WTP for higher quality rivers, streams, and lakes. Several studies have estimated WTP for water quality improvements in different contexts. These studies can provide relevant estimates for benefits transfer. Applying this method requires data on the baseline level of water quality, expected water quality improvements resulting from the project, and the scale of water quality improvements relative to water quality impairments within the local municipality/watershed.

Avoided infrastructure costs

If the baseline scenario includes an alternative project for addressing water quality impairments, the costs of the avoided project can be included as a benefit of the green infrastructure or nature-based resilience project. Costs of the avoided project should include lifecycle costs – from design, construction, to annual maintenance. Costs should be calculated for the period over which the project would have been implemented for appropriate comparison in present value terms. Consideration should be given to the expected life of the avoided project. For example, if the nature-based resilience project has an expected life of 50 years (or is being evaluated over a 50-year period), and the avoided project has a useful life of 30 years, replacement costs (or decommissioning costs as relevant) incurred at the 30-year mark should also be included as an avoided cost.

Household willingness to pay for water quality improvements

The WRF green infrastructure TBL Tool allows users to calculate household WTP for water quality improvements. This method can be used to approximate the value of water quality improvements for an individual project by estimating how much the project contributes to overall waterbody health. It requires some judgement from the user to make reasonable assumptions related to key inputs; it is intended to provide a reasonable approximation of value associated with the average change in water quality and aquatic habitat across affected/target water bodies. Follow the steps below to estimate benefits to water quality:

Step 1: Determine level of water quality improvement in affected water body
The ten-point water quality ladder serves as the basis for measuring the water quality improvements that will result from a green infrastructure project. This in turn influences household WTP for those improvements.

Using the water quality ladder (see figure to the right), estimate current water quality conditions prior to the project. For example, if a water body is currently acceptable for rough fishing and provides satisfactory habitat for some wildlife, it would receive a rating of 4.3. The table shown below the water quality ladder can help to inform these judgements.

Next, based on the expected outcomes of the project, estimate the extent to which the green infrastructure project or nature-based solution will improve water quality for the area it impacts, and the number of points that this improvement will represent. For example, if the project was expected to improve water quality from a 4.3 to a 5.3 on the water quality ladder, the expected improvement would be 1 point.

Step 2: Estimate household willingness to pay for water quality improvements
The WRF Green Infrastructure TBL Tool requires the following inputs to estimate household WTP for water quality improvements, including:

• • • Whether the water quality change occurs in an estuary
    • Whether the water quality change affects only local freshwater bodies (i.e., those within a city or a small portion of a state) – this should be a “Yes” for the types of projects covered here.
    • State in which the project is located
    • Median household income for the local area (deflated to 2010 dollar value)
    • Whether the affected water body supports recreation, and if so, the percent of affected population that use the resource for recreation

Step 3: Scale total value to estimate benefits of individual project
The next step is to scale the percentage of total WTP or households that should be included in the calculation of for the project(s) being analyzed. This will vary depending on the nature and scale of the project but can be determined in several ways. For example, the user may base it on the percentage of total stream miles affected in a watershed or the percentage of a total stormwater management goal that the project helps to meet (e.g., number of greened acres, percentage of uncontrolled impervious acres treated, percentage of total costs necessary to meet TMDL requirements or a city’s stormwater management goals). The green infrastructure TBL Tool calculates the total value of water quality improvements by multiplying average household WTP by the number of households and the “percent project contribution” values entered by the user.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool) is one of the easiest ways to calculate the value of water quality benefits in this context. The tool requires inputs for water quality baseline point value and point improvements, recreational usage estimates, percentage of improvements to estuaries, household median income, and the number of households impacted.

The US Census Bureau American Community Survey (ACS) data contains household level information that can be used as WRF Tool inputs. Necessary information can be found in a Census area’s location profile, which are one of the first results when searching for a place. Alternatively, ACS tables “B19013” and “CP04” contain data on median household income and total households, respectively. Applying the impacted location as a filter on the Census data website yields the data for the relevant location.

Quantifying the recreational benefits of nature-based resilience projects requires knowledge of the types of recreation available at a site, current visitation levels (if the site currently supports recreation), and a project’s ability to increase recreational opportunities, use, and enjoyment.

Recreational visits are associated with a person’s WTP to participate in a recreational experience, also referred to as a direct use value. This value reflects the quality and enjoyment associated with a recreational experience, and can vary by activity type. Direct use values represent WTP per visit to participate in a recreational activity.

The total value of recreation at a given site is a function of direct use values and the recreational trips (often referred to as “user days” or visitor days) taken to the site. Factors that affect visitation and/or direct use values include the type and quality of recreational amenities available at a site, the availability of similar recreational opportunities nearby, characteristics and proximity of residents, ease of access, and the aesthetic nature of the site

Estimating the economic benefits of recreational amenities is a three-step process.

Step 1: Estimate the number of new recreational users by activity type
Recreational benefits depend on the number of new recreational visits to a site each year, as well as the primary activities in which visitors participate.

For sites that currently support recreation but where the proposed project will increase or enhance recreational opportunities, increases in recreational use may reflect an increase in the frequency of visits by existing users and/or the addition of new users. For projects that will create new recreational opportunities, most visits may be considered “new visits.” However, the number of new visits may need to be adjusted downwards if there are several similar recreational opportunities nearby (i.e., in this case, some visits may be a transfer from one site to another rather than a true net gain in recreational visits).

The WRF Green Infrastructure TBL Tool contains a module that allows users to estimate visitation to neighborhood “pocket parks” and to larger parks. Local planning documents and data can also provide insights into a site’s existing recreational use. Planners can use this information to evaluate the impact of an assumed percentage increase in existing visitation. In absence of sufficient data, rules of thumb can be applied to estimate visitation. A project’s proportional impact may be useful a proxy for estimating the increase in recreational opportunities. For example, if a project increases total green space in a neighborhood by 10%, it can be assumed that the project generates a 10% increase in community recreation. Visitation may also be estimated based on assumptions regarding the average number of visits per year by households located within a certain distance of the area.

Relatively simple information regarding participation by activity type is needed at this stage. Specifically, if a site offers fishing, hunting, boating, or a specialized activity, the percentage of visitors that participate in these activities should be estimated. All other activities can be considered “general recreation” for the purposes of valuation.

Step 2: Determine direct use values
It can be challenging to determine direct use values, as original estimates rely on stated preference surveys and/or revealed preference studies. In some cases, local or state studies may report direct use values for different activity types. These values can be applied using benefits transfer to estimate the value of recreation associated with a project.

When local data is unavailable, the US Amy Corps of Engineers (USACE) Unit Day Value method can be used to estimate direct use values. This method allows users to calculate values for general recreation, fishing and hunting, and specialized recreation activities based on site characteristics. It can be used to estimate differences in direct use values for projects that enhance recreational opportunities and/or quality at existing recreational sites, as well as for projects that create new recreational opportunities.

The Oregon State Recreation Use Values Database is another potential resource for direct use values. It provides national and regional values for specific recreational activities.

Step 3: Calculate project benefits
In this step, multiply the number of new recreational user days by activity type (i.e., number of new visits relative to the baseline) by the corresponding direct use value to calculate the project’s total recreational benefits.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool) utilizes the USACE methodology for estimating direct use values associated with recreational opportunities generated by green infrastructure projects. It also helps users estimate visitation to community parks, pocket parks, and wetland areas, and recreation associated with general neighborhood greening. The methodology employed is applicable to both small and larger scale nature-based projects that create or enhance recreational sites.

US Amy Corps of Engineers (USACE) Unit Day Value method can be used to estimate direct use values.

The value of habitat improvements can be difficult to quantify because habitat and biodiversity are generally not bought and sold in a market. As result, quantifying this value depends on the methods economists have developed for valuing “non-market” goods and services. For example, stated preference methods use advanced survey techniques to elicit estimates of WTP for specified improvements in – or avoided degradation of – habitat or water quality, based on the species affected, nature of the improvements, and other local factors. Units are typically in terms of WTP per household or totaled to produce total WTP per acre of habitat.

The simplest approach for valuing habitat is to apply per acre values to the new or restored habitat area. This requires information on the project size/footprint, type of vegetation/land use, and applicable WTP values. In some cases, a project might benefit a key species, including a threatened or endangered species. In these cases, studies may be available that report higher values for WTP due to the unique nature of the site. To estimate these values, practitioners can search academic literature to find applicable benefit transfer values (see description of Ecosystem Values Reference Inventory, EVRI, below).

High level habitat values can be estimated using benefit transfer of published per acre habitat value. Follow the steps below to estimate benefits to wildlife habitats and biodiversity.

Step 1: Define the habitat area/type
The first step is to determine the new or restored area of habitat, the type of habitat/and use, and key species that could potentially benefit from the project. When restoration occurs over existing habitats, the impacted area may be estimated based on a percentage of total restored land, the extent of improvements, and prior degradation. This requires some professional judgement.

Applying per acre habitat values is the simplest approach and more accurately reflects aggregate WTP by all households. However, some projects may be more unique in that they provide habitat for highly values species (e.g., threatened or endangered species). Studies may be available that estimate WTP per household for providing habitat for these species. To apply these studies, an estimate of the number of households located within a certain distance of the project is necessary. The distance will depend on the scale of the project and may be determined from the study being relied on for benefit transfer estimates. This approach would require some professional judgement.

Step 2: Apply WTP values
The next step is to determine the applicable WTP values for the project. Two key sources can be used. The FEMA Benefit Cost Analysis Toolkit (BCA Tool) is an Excel-based tool that is publicly available for use. The tool helps users assess ecosystem service benefits associated with nature-based flood mitigation actions based on the land use types associated with their project (e.g., urban green space, wetlands). The tool values ecosystem services across four categories (consistent with the widely recognized ecosystem services classification framework) and for 14 subcategories. Values taken from academic literature are applied to each subcategory by land cover type, resulting in dollar per acre estimates. Table 2 shows values for the habitat subcategory for relevant land use categories. For urban green space, FEMA also reports a pollination value of $406 per acre per year (2024 USD). This can be added to the habitat value.

Another resource is the WRF green infrastructure TBL tool, which provides national average estimates for different green infrastructure types (Table 3). The values in the Tool are based on existing research related to wetlands and a relative comparison of the habitat values associated with other green infrastructure practices.

Rare habitat or habitats that provided unique ecological benefits can have higher WTP values associated with their protection. Teams determining the WTP for ecosystem restoration and improved biodiversity should note the higher WTP values for habitats such as estuaries, sea turtle nesting dunes, spawning streams, and other rare or endangered ecosystems.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool)contains a module for valuing habitat and biodiversity benefits associated with green infrastructure practices and projects.

FEMA Ecosystem Service Values (June 2022) provides ecosystem service values for a range of categories, including habitat and pollination, by land use type.

Environmental Valuation Reference Inventory (EVRI) is a searchable database of summaries of environmental and health valuation studies. The EVRI is a Canadian-run resource that provides information on the economic value of environmental benefits and human health effects. The database includes summaries of over 5,000 valuation studies, with information on the study location, the environmental assets being valued, the methodological approaches, and the estimated monetary values.

Information on the amount of carbon sequestered by trees and other types of vegetation is necessary to estimate carbon reduction benefits. This varies over time and by vegetation type, and can involve complex modeling to produce precise estimates. However, average annual carbon sequestration rates (e.g., per tree or per square foot of vegetation) can be applied for the purposes of high level benefits analysis.

If a nature-based resilience project reduces energy use through building energy savings and/or avoided stormwater pumping and treatment, it is necessary to estimate the total energy savings and associated avoided GHG emissions. Emission rates from power generation depend on regional fuel resource mix and other factors. Publicly available data from the U.S. EPA reports CO₂ and other GHG emission rates from electricity production (by U.S. region), in terms of pounds per MWh of electricity produced.

Economists typically value the benefits of CO₂ reductions using the “social cost of carbon” (SCC), which represents the aggregate net economic value of damages from climate change across the globe. In 2016, the U.S. Government’s Interagency Working Group (IWG) on Social Cost of Carbon issued updated guidance on recommended SCC values (per ton of CO₂) for regulatory benefit-cost analysis. The Working Group’s estimate reflects the worldwide net benefit of reducing one ton of atmospheric CO₂, on average.

Follow the steps below for estimating benefits of carbon sequestration.

Step 1: Estimate carbon sequestration from new vegetation
The first step is to estimate the amount of CO2 removed from the atmosphere by green infrastructure or nature-based resilience projects. Table 4 shows average annual carbon sequestration by trees for different climate regions of the U.S. (see map below).

These estimates were calculated using i-Tree tools (developed by the U.S. Forest Service, USFS) and information from the USFS on the typical mix of tree species by region and their average size.  They reflect the amount of carbon sequestered by trees at full tree growth (assumed to be 30 years and beyond), and have been translated from carbon (C) sequestered from the atmosphere to equivalent reductions in CO2. To estimate benefits over time, these estimates can be scaled over 30 years. A simple way to do this is to assume that a newly planted tree (year 1) would capture 10% of the amount of carbon sequestered in year 30.

Carbon sequestration rates for other types of vegetation vary. The WRF Green Infrastructure TBL Tool applies the following assumptions to estimate carbon sequestration for different types of nature-based resilience projects. These estimates can be used as rules of thumb:

• Wetlands: 0.41 kg CO2/m2 per year
• Bioretention, rain gardens, and bioswales 1.01 kg CO2/m2 per year
• Green roofs: 2.04 kg CO2/m2 per year for three years post implementation. Green roof capacity to store carbon is limited, as their soil substrate is often between 3 and 12 inches. This means that after a few years they typically reach equilibrium in terms of net carbon storage.

Step 2: Estimate CO2e emissions reductions
Building energy savings from trees and green roofs can be estimated using USFS i-Tree software and the National Green Roof Energy Calculator, respectively. Table 5 also shows energy savings from street trees by U.S. climate region (estimated using i-Tree tools and information from the USFS on the typical mix of tree species by region and their average size), which can also be used for this purpose. For combined sewer communities, the WRF Green Infrastructure TBL Tool reports national average energy use associated with stormwater pumping and treatment as 2,000 kWh/MG and 2,520 kWh/MG, respectively. These estimates can be tailored to individual projects and communities.

Table 6 shows emissions rates for CO₂ equivalents (which translate all GHGs into an equivalent CO₂ unit). It also shows average electricity grid loss percentages. This data is published by the U.S. EPA for different energy producing regions of the U.S., referred to as eGrid regions.

To calculate avoided emissions, multiply the avoided energy use associated with green infrastructure/nature-based resilience projects by the relevant emissions rate for the relevant eGrid subregion (see map), accounting for grid transmission losses. For example, an energy savings of 5 MWh per year in the ASCC Alaska Grid (AKGD) would be multiplied by the corresponding avoided emission rate of 1,058 lbs/MWh, and again by the transmission loss rate of 5.00% plus 1. This yields an estimate of 5,555 lbs of CO_2eemissions avoided per year (5 MWh * 1,058lbs/MWh * 1.05 = 5,555 lbs CO2e).

Step 3: Value carbon reductions using Social Cost of Carbon
The final step is to apply the SCC to estimate the monetary value of carbon reductions each year. Table 7 shows SCC estimates for different years, reported in 2024 USD (in present value terms, assuming a discount rate of 3%). Increases in the SCC in later years are above and beyond inflation; this is because increased damages will occur from carbon over time as population grows and damages become cumulative. While the table shows SCC estimates in 5-year increments, values can be interpolated for intermittent years.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool) contains a module that allows users to calculate the carbon reduction values associated with various green infrastructure practices.

i-Tree is a software suite developed by the USDA Forest Service that allows users to estimate the full range of benefits provided by trees and forests. It calculates carbon and pollution reduction benefits from trees and energy savings, in addition to other benefits. Depending on the module, users input tree characteristics, lifespan, and project details to place tree projects in a specific area.

National Green Roof Energy Calculator is an online tool that allows users to estimate the energy savings and other benefits of green roofs in 100 U.S. cities.

Economic benefits to businesses

Greening multifamily residential buildings, shopping areas, and commercial corridors can increase neighborhood aesthetics, which in turn can increase rental rates and retail sales. Several studies have found that green infrastructure and similar nature-based improvements attract more customers, enhance customer experiences, and create reputational value for the business.² Studies looking at the effect of greening urban business districts and strip malls have concluded that consumers are willing to pay a premium on products, visit stores and restaurants more frequently, or travel farther to shop in areas with attractive landscaping, good tree cover, or green streets.³

Community enhancements and economic development

Nature-based resilience projects can provide significant quality of life and neighborhood improvement benefits when specifically designed for this purpose. For example, programs that pair stormwater management opportunities with vacant lot revitalization, community gardens, safe routes to schools, or neighborhood parks and green spaces can result in multiple benefits for residents, including human health benefits, community cohesion, and improved economic vitality. Larger-scale green infrastructure projects such as stream restoration or other projects that create recreational opportunities can attract new businesses, spur investments, and provide recreational opportunities that attract visitors.²

Value of neighborhood improvements

The value of nature-based improvements for local businesses and residents are often reflected in increased property values or rental rates, and/or enhanced economic activity (e.g., increased economic output or sales). The documentation associated with the WRF Green Infrastructure TBL Tool reports that well designed nature-based solutions can increase single family home values by as much as 7% to 12%, depending on the type of improvement, but that most estimates seem to range from 1% to 5%.

A study published by the Natural Resources Defense Council (NRDC) reports the following benefits from green infrastructure projects for office buildings, multi-family residential buildings, and retail centers based on the following estimates from the literature:

Economic multipliers or more comprehensive economic impact assessments (EIAs) that rely on input-output models can be used to examine the impact of increased economic activity within a region. These are described in more detail below.

• Multi-family residential property values increase from 2% – 5%
• Shade & landscaping increase rental rates for office buildings by 7%
• Rents in multifamily residential buildings with green roofs can be upwards of 16%, but typically within the range of 7% -10%
• Shoppers willing to pay 8% – 12% higher prices for shopping in areas with tree canopy

Economic multipliers or more comprehensive economic impact assessments (EIAs) that rely on input-output models can be used to examine the impact of increased economic activity within a region. These are described in more detail in the next section.

Community enhancement benefits (measured through increased property values)

To measure the value of aesthetic improvements associated with nature-based solutions and green spaces, economists typically employ “hedonic pricing” methods, which use statistical analysis to estimate the effect of different factors on the price of a home or property. Hedonic models attempt to isolate the effect of a specific characteristic, such as proximity to green infrastructure, on a property’s market value by controlling for all other factors. Developing hedonic models to assess property value increases is a time-consuming and resource intensive task. For a high level benefits assessment, practitioners can apply findings from existing well-executed studies on this topic. This approach is known as benefits transfer. The following describes key steps and considerations for applying benefits transfer in this context.

Step 1: Identify the properties affected by the project.
This step involves applying professional judgement to identify the properties that would likely realize an increase in value because a green infrastructure or other nature-based resilience project is located nearby. Factors to consider include the scale of the green infrastructure project, the level of existing green space, landscaping, and/or tree canopy in the area, and any amenities provided by the project. For example, a green roof or rain garden located on a property might influence only the value of that property, while a green street or public open space would have a much greater impact, including for adjacent properties and beyond. In evaluating the effect of distributed green infrastructure, a study conducted in Philadelphia found property value increase for projects located within a quarter mile of green infrastructure improvements.

Step 2: Estimate the property value baseline for single family residential multi-family properties.
This information can be obtained from the American Community Survey (ACS), at the city or even Census tract level. The WRF Green Infrastructure TBL Tool offers a methodology and specific instructions for accessing and applying this data. Alternatively, many utilities may have access to more comprehensive local databases, such as through the County Assessor’s office that will allow them to calculate baseline residential and commercial property values. Online tools such as Zillow, which estimates home sale prices can also be used to estimate baseline property values.

Step 3: Apply property value increases from the literature to the aggregate value of affected properties.
The percent property value increase that might be expected from a nature-based resilience project(s) also requires some level of professional judgment. As in Step 1, factors include the type and scale of the project, the level of existing green space, landscaping, and/or tree canopy in the area, and any amenities provided by the project. Table 8 provides a range of estimates from the literature for property value increases associated with different types of nature-based practices.

Table 8. Range of property value increases from green infrastructure and nature-based practices, based on literature review of hedonic studies

As an important note, the property value increases associated with nature-based projects can reflect WTP for a range of benefits. Thus, property value increases are also likely capture other project benefits, such as related to recreation or flood risk reduction. As a rule of thumb, applying 50% of total property value benefits when summing benefits across categories can help to avoid double counting.

Economic impacts

Economic multipliers or more comprehensive EIAs can be used to examine the impact of increased economic activity within a region. For example, an EIA can estimate how increased visitor spending associated with an improved recreational site flows through the local economy, creating positive economic output and employment impacts. These same methods and tools can be used to estimate the effects of value added development or increased retail that occurs within a city or town because of a comprehensive nature-based project.

To estimate the economic impacts associated with a resilience project, a team can utilize state- or local- (e.g., County) level economic multipliers (e.g., published by the Bureau of Labor Statistics and the Bureau of Economic Analysis) or more comprehensive input-output models such as IMPLAN ,which is available (for purchase) for every county in the U.S. Multipliers and input-output models capture the ripple effects associated with increased economic activity in a local region, including direct, indirect, and induced impacts. For example, a resilience project that increases recreational opportunities and attracts visitors from outside the region, results in increased tourist spending (direct effects). Businesses that benefit from this increased spending purchase supplies from other local industries (indirect effects). Households employed by impacted businesses and industries benefit from this additional activity and often spend more money (in aggregate) in the local economy as employment increases (induced effects). Economic impacts are different than economic benefits (as they represent a transfer). Economic impacts (and particularly indirect and induced effects) should not be added to economic benefits used for benefit cost analysis purposes. Use of multipliers and input-output models typically require some level of expertise with EIA concepts to ensure the methodology is correctly applied.

Water Research Foundation (WRF) Green Stormwater Infrastructure Triple Bottom Line Tool (Green Infrastructure TBL Tool)contains a module that helps users quantify the property value increases associated with green infrastructure projects, walking users through data sources and key considerations for applying benefits transfer in this context.

IMPLAN is a cloud-based economic input-output model that allows users to calculate economic impact assessments at various scales. Data and modeling is available for all counties within the U.S. for purchase.

Green Infrastructure Impact Hub Guide to Understanding and Monetizing the Job Creation and Economic Development Benefits of Green Stormwater Infrastructure (2024).