As the body of knowledge surrounding the impacts of infrastructure projects on surrounding communities grows, Low Impact Development (LID) and Green Infrastructure (GI) designs are being increasingly chosen over their ‘grey’ alternatives. GI/LID projects can result in positive externalities, or spill-over benefits, to local communities, including improved local water quality, habitat enhancement, increased recreational space, reduced flooding risk, improved health, and improved air quality.
These benefits can vary based on the type of infrastructure being built, as well as the location of the project. The benefits of investing in a stormwater management project with GI/LID characteristics in a hot and dry climate, for instance, will have to be calculated while considering region-specific variables, including scarcity of resources, local population characteristics (e.g. population density, income), and local weather patterns. Determining a reliable and agreed upon method to quantify these benefits is the key to enabling universal adoption of GI/LID practices into infrastructure development.
In more humid parts of the country, it is easy to intuitively imagine that premiums from investing in GI/LID practices can be justified by considering impacts on water quality and water usage alone. Many of these communities have combined sewer systems, so excessive rain events can lead to sewer overflows, resulting in high contaminant and bacteria levels in local bodies of water. This damages local habitats, reduces the amount of recreational space (water is often not suitable for swimming for several days until the levels of bacteria drop), and poses health risks to local residents. GI/LID practices can be cost-effective in these regions because they enhance the potential for reducing or eliminating the risk of these sewer overflows. Furthermore, the potential for contaminant migration in stormwater tends to be more limited in hot and dry environments because bodies of water are few and groundwater is deep.
Stormwater management in hot and dry environments also has particular importance because the use of stormwater can offset the reliance on other potable water sources. Similarly, vegetation watered with stormwater has the potential to decrease energy usage as well as reduce risks of depletion of other sources of water, such as underground aquifers. So, environments where water is scarce can see substantial impacts from GI/LID practices in stormwater management projects due to both improved local water quality and quantity.
GI/LID practices can also improve quality of life by reducing the urban heat island effect. Especially in areas where the climate is very hot and dry, the inclusion of enhanced green building characteristics into an infrastructure project can reduce local temperatures, leading to substantial impacts on the health and even the mortality rate of local residents. The Center for Neighborhood Technology (CNT) produced a report discussing the benefits of GI practices, including the effects on urban heat islands. “The urban heat island (UHI) effect compromises human health and comfort by causing respiratory difficulties, exhaustion, heat stroke and heat-related mortality … Various studies have estimated that trees and other vegetation within building sites reduce temperatures by about 5°F when compared to outside non-green space. At larger scales, variation between non-green city centers and vegetated areas has been shown to be as high as 9°F.” Reduced temperatures can be a large benefit for a project.
The largest problem being faced is not in convincing decision makers that, qualitatively, the benefits from GI/LID practices are worthy of a premium investment; the main hurdle is the need to justify the usual premiums that accompany GI/LID projects from a quantitative perspective. As a result, agreement over a method to quantify the value of these impacts between project categories, as well as between different locations, is crucial to drive adoption of GI/LID practices. To help overcome this hurdle, some communities are creating GI/LID Guidance Manuals to facilitate the adoption of green practices. In reality, it will likely require a combination of guidance manuals, some policy, and tools that quantify the benefits of infrastructure projects to make the business case for GI/LID adoption.
 The Value of Green Infrastructure – A Guide to Recognizing Its Economic, Environmental and Social Benefits, Center for Neighborhood Technology 2010, p. 14, downloaded from: http://www.cnt.org/repository/gi-values-guide.pdf . September 27, 2013.