Green infrastructure encompasses technologies and practices that use natural processes (or artificial systems that simulate natural processes) in order to improve the overall quality of the environment and provide social, ecological, and economic benefits. Green infrastructure is based on the idea that human societies can benefit from the protection of natural ecosystems and from the integration of these very ecosystems and natural processes into territorial planning and development.

Two key characteristics of green (or natural) infrastructure are its interconnectivity and multifunctionality. The first term highlights the importance of linking natural and man-made ecosystems and connecting natural processes to human infrastructural needs. The multifunctionality aspect refers to the ability of green infrastructure to deliver multiple benefits, meaning that the adoption of a nature-based strategy can provide versatile solutions for decision makers.


Green Infrastructure Can Reduce Flood Risks

The world faces a range of water-related challenges that are set to intensify over time. Increasing water demand, decreasing water availability, deteriorating water quality and extreme weather-related events are contributing to worsening global water security. All these problems can be mitigated—to different extents—by appropriate infrastructure.

Infrastructure can ensure that controls are in place to mitigate or avoid water contamination, promote resilience in the face of flooding or droughts, and curtail water withdrawals and reduce water losses in various processes. Green infrastructure stands out for its ability to create solutions to these problems through the restoration and preservation of natural ecosystems, which in turn contribute to enhanced water security.


Case Study: The Yolo Bypass - From Water Management to Food Security and Wildlife Protection

Yolo Basin Wetlands (Courtesy Pxhere)

Most of California’s territory is prone to flooding. The Public Policy Institute of California holds that “one in five Californians and more than $580 billion worth of structures are vulnerable” to floods. Severe flooding can disrupt a number of sectors, including transportation, energy, water supply, agriculture and sewer networks.

A system of canals, reservoirs, dams and bypasses make up California’s water management system. This web of grey infrastructure supplies water to the agricultural and industrial sectors and to residential users, while also being used for flood management and hydropower generation. But in terms of flood prevention, the system has often failed to meet expectations and has also resulted in a series of negative impacts on the Golden State’s natural ecosystems. Around 95 percent of California’s wetlands have disappeared since the late 1800s due to a combination of unprecedented growth in grazing and the construction of water and flood control projects. This has resulted in decreased water supply in cities spanning from the Bay area to San Diego and in water shortages for farms within the southern Central Valley, which have experienced declining crop yields and soil quality due to increasing salinity levels.

California’s Yolo Bypass represents a green infrastructure success story in the state’s water management system. In the early 1900s, after decades of flooding in the Sacramento Valley, engineers started realizing that the practice of building levees close to the main channel to transport mining debris downstream was narrowing the river channels, increasing the water level and the risk of floods in large storm events. In order to provide for higher flow capacities to protect the population from floods, a new solution was developed mimicking the natural aquatic system of Sacramento River’s floodplains.

This effort resulted in the construction of a network of weirs and bypasses, including the Yolo Bypass, which became part of the Sacramento Flood Control Project developed by the U.S. Army Corps of Engineers. By the early 1930s, much of the system had been installed. Presently, when the Yolo Bypass floods, it generates a wide shallow water habitat covering around 24,000 hectares.

The Yolo Bypass has been providing flood protection to Sacramento residents for almost 90 years now, but its functions are not limited to flood control. In terms of land use, when the Bypass is not flooded, it is dominated by agriculture, which takes up about two-thirds of the area, producing rice, wild rice, sugar beets, tomatoes, safflower and corn, representing a key production zone for Yolo County, which relies on agriculture as a source of revenue.

The remaining one-third of the Bypass area consists of wetlands, perennial wetlands, riparian forests, pond areas and riparian uplands, constituting a natural ecosystem for the region’s wildlife. The Yolo Basin Wetlands, with its 1,250 hectares, is one of the largest wetlands projects in the western United States, providing an essential stopover for more than 200 species of migratory birds. The wetlands are home to 42 species of fish (15 of which are native) and sustain the highest salmon population in California thanks to phytoplankton-rich waters.

The Yolo Bypass is a good example of how a green solution to a water management problem (flooding) can yield multiple positive results in different fields. The Bypass also shows how an engineered system can still embody the principles of green infrastructure and deliver the same benefits.


Green Infrastructure Can Reduce Water Runoff While Growing Food

Agriculture has a large environmental footprint. Currently, it accounts for about 70 percent of global water withdrawals and will remain the largest user over the coming decades. Nevertheless residential and industrial demand for water is set to increase at a faster pace throughout the world, due to urbanization and industrialization. Agriculture will, therefore, face stress from its own increased water demand and also from fiercer competition for water from other sectors. Climate change will add to this stress, by affecting the seasonal timing of rainfall.

Agriculture requires vast amounts of land, which, in combination with its water needs, often results in changes to aquatic and terrestrial ecosystems. As highlighted in the first case study, the removal of existing natural structures (wetlands, trees, marshes, floodplains) can negatively affect the ecosystem and create long-term and structural issues that affect water, food, energy and human security.

But agriculture can also become a solution. If on the one hand, it weighs immensely on the water system and on natural ecosystems, on the other, if sustainably managed, it can provide multiple benefits.


Case Study: Urban Farms Reducing Water Runoff in New York

Urban farm systems take many forms, ranging from individual to community farms, and from rooftop gardens to urban orchards, but they are all commonly defined as the “production of crop and livestock within cities and towns.” Urban agriculture can include the cultivation of fruits, vegetables, spices, medicinal plants, mushrooms, and other types of productive plants.

From a food security perspective, urban agriculture represents a way to reduce cities’ lack of access to fresh produce. In particular, it can provide fresh produce to low-income residents who have limited access to bigger supermarkets usually located outside city centers. Urban agriculture can also decrease the price of food by eliminating transportation costs.

New York City is a prime example of how urban agriculture can provide increased access to fresh produce and lower prices while also addressing stormwater management. Along with many other cities, New York is facing problems arising from decaying infrastructure (extremely stressed urban water systems) as well as changes in precipitation patterns and increases in extreme weather events—both due to climate change. In particularly wet seasons, the city faces floods, raw sewage releases, sinkholes, and road washouts. An overwhelmed stormwater pipe system can lead to polluted runoff, decreased surface water quality, and increased energy consumption for wastewater systems.

New York has a combined sewer system, meaning that the same network of pipes is used to collect stormwater, domestic sewage and industrial wastewater. Unfortunately, New York wastewater treatment plants were not originally designed for a combined sewer system; they were meant to treat only sanitary waste. In wet seasons, the combination of these two factors makes New York particularly prone to untreated stormwater overflows, which, combined with untreated sewage and wastewater, end up contaminating nearby water bodies.

In light of these daunting challenges, the New York City Department of Environmental Protection has opted for a green infrastructure strategy to provide a sustainable urban solution. In 2010, New York City released the New York Green Infrastructure Program, which tackles the stormwater problem by trying to reduce water runoffs reaching the sewage system. This reduces the need for end-of-pipe stormwater storage and costly interventions in wastewater treatment plants. As of 2017, the Green Infrastructure Program had more than $410 million in funding, with an additional $1 billion earmarked for the next 10 years.

Since 2011, the Department has also committed $15 million to fund more than 30 green infrastructure projects in coordination with private property owners through the Green Infrastructure Grant Program. As a result of these investments, which were also supported by local nonprofits and the New York community gardening program GreenThumb, more than 500 community gardens were created across the city allowing families and individuals to grow food and providing communities with green spaces used for multiple social and recreational activities. Of these 500 community gardens, roughly 140 use rainwater-harvesting systems with a calculated total holding capacity of over one million gallons.

The Brooklyn Grange's rooftop urban farm
(Courtesy: Tania Gustave)

One of the main examples of the Grant Program’s successful urban farm projects is the Brooklyn Navy Yard and Brooklyn Grange project. With an initial investment of about $593,000, the city repurposed the industrial buildings that make up the Navy Yard, which previously served as a shipyard in the Second World War, and created one of the “world’s largest roof-top soil farms.” The Grange Farm covers almost one acre and is located on the roof space of Building No. 3. A variety of organic produce is grown in this urban agricultural space, including more than forty varieties of tomatoes, carrots, peppers, radishes, salad greens, and herbs. The farm is also home to a commercial apiary and keeps egg-laying hens. The produce is sold to community members, to local retail stores and restaurants, as well as to the larger public in weekly farmers’ markets in different neighborhoods. In terms of its impact on the water system, the Grange Farm collects roughly 3,700,000 liters of storm water per year (more than a million gallons) thanks to its permeable rooftop and agricultural water usage, helping reducing the combined sewer system flow into the East River.


Green Infrastructure Can Help Keep Hydropower Power Plants Running

In terms of global water withdrawals, the energy sector is second only to agriculture. The electricity generation sector represents the largest source of water withdrawals within the energy sector, while primary energy production (pumping oil and mining coal, for instance) is larger in terms of water consumption. Thermal power plants constitute the main source of water demand in the electricity generation sector, withdrawing large amounts of water (mostly surface water) that is used in the cooling process. Depending on the cooling technology, the quantities of water needed vary, along with the impacts on energy production costs and on water quality.

With regards to primary energy production, the quantity of water consumed depends on the type of fuel and on the stage of the fuel cycle (extraction, processing or transport). Both the extraction and processing of fossil fuels need large amounts of water, while energy production in general can degrade the quality of water and alter river flows’ timing, negatively impacting aquatic ecosystems.

Green infrastructure can represent a solution to certain water-related problems arising from the energy sector. Aside from preserving the water ecosystem and water resources in general, green infrastructure can be employed to increase the energy efficiency of power generation. When integrated with grey infrastructure, such as dams for hydroelectric power, green infrastructure can improve their longevity and efficiency.


Case Study: Hydropower in Costa Rica

The Pirris hydropower dam in Costa Rica
Credit: Tarrazu

One of the major issues in the management of artificial reservoirs, such as dams for hydroelectric power, is the gradual accumulation of sediments, which reduces the dam's storage capacity, limiting its functionality. Sedimentation also affects the dams’ safety, reduces production and discharge, causes abrasion and damage to various mechanical components, and increases the risk of floods. It is therefore necessary to control and limit sedimentation in dams. Green infrastructure solutions like reforestation of the watersheds above dams, can prevent soil erosion and naturally slow down the sedimentation process.

Hydropower accounts for more than 75 percent of Costa Rica’s electricity production, representing the largest source of energy in the country. In the 1990s, the hydroelectric sector in Costa Rica faced a serious crisis when landowners upstream of the dams started clearing land for agriculture and grazing. Deforestation then resulted in soil erosion, which caused higher levels of sedimentation in the reservoirs. The dams’ capacities diminished and turbines started deteriorating.

In order to address the issue, Costa Rica established the National Fund for Forest Financing (FONAFIFO) in 1995, which provides incentives for small and medium landowners and producers to contribute to forestation, reforestation and afforestation. Costa Rican hydropower company Energia Global (now Enel) and the government (financed by fuel and water tax revenues) both pay into the fund. The fund, in turn, makes cash payments to the upstream landowners who agree to reforest their lands, engage in sustainable forest-related practices, and generally preserve forests. The fund’s instalments ($48 per hectare per year) cover the opportunity cost of forgone land development for plantations and cattle raising.

Since its inception, the program has achieved important environmental improvements on roughly one million hectares, with the participation of more than 10,000 landowners. The restoration of the trees since has decreased soil erosion and, consequently, slowed down the sedimentation process, increasing the water storage and improving the general function of the hydroelectric dams. This type of green infrastructure solution also benefits the landowners by providing them with a fixed income for their good practices. At the same time, the restoration of the watershed’s vegetation through a reduction in grazing results in a healthier habitat that can host a richer variety of species, benefitting the aquatic and terrestrial ecosystems. Finally, a substantial increase in trees and green plants helps absorb carbon dioxide from the atmosphere, mitigating climate change.


Green Infrastructure Challenges

The most critical challenge green infrastructure faces at the moment is the lack of a well-structured, comprehensive and established way to calculate its costs and benefits, especially in comparison to grey infrastructure. This results in the generalized hesitance of decision-makers, industries, and public sector officials to invest in green infrastructure. Without substantial literature showing the economic and financial benefits green infrastructure solutions can provide, decision makers will be loath to commit resources to such projects. They need to be persuaded that green infrastructure is not only good for the environment, but also for their revenues and budgets.

Financial and economic assessments for green infrastructure have started to emerge, and a number of research centers and governmental institutions have been delving into the issue and have begun producing some interesting results. For instance, the U.S. Center for Sustainable Economy has developed a Green vs. Grey Analysis (GGA), which provides a framework to financially compare grey and green infrastructure solutions to determine whether investments in green infrastructure can represent a more cost-effective strategy. As more green infrastructure projects are completed and yield long-term results, such initiatives will have more data to work with, making their models more accurate.

Another, related, challenge is the financing of green infrastructure. The fundamental difference between grey and green infrastructure financing stems from the fact that the former relies on a top-down type of financing that has well-established, consolidated structures and mechanisms. With green infrastructure, financing needs to be structured in a different way, dictated by the unique characteristics of the natural solutions that are employed. For instance, Costa Rica had to find the right incentives to get landowners to protect forests on their lands. In New York, public authorities provide subsidies to private households and companies to engage in the urban farming effort. This type of financing requires a different kind of mindset, showing flexibility and openness to new market solutions. But this bottom-up approach might be difficult to scale up and could also represent a barrier to big private investors, who do not usually engage with the public.

Finally, the third major challenge to green infrastructure is the reluctance of policy-makers to adopt a less sector-specific perspective. By and large, the linkages between water, energy and food have been theoretically accepted, but in practical terms, it is still common to opt for a solution that addresses one specific problem, mainly because it is the established way of dealing with it. The same issue is present when policy-makers evaluate how to solve an infrastructure problem or fulfill an infrastructure need. Grey infrastructure constitutes a body of well-established practices, the mechanics, costs and purposes of which are known. It is just simpler to walk a well-trodden path, whereas it is very difficult to change a mindset that sees technological innovation and nature as separate and almost conflicting entities. Fortunately, in many cases green infrastructure can be developed at a very small scale, with very low costs. Modest initiatives at the community-level can lay the basis for the establishment of green infrastructure practices that will serve as blueprints for bigger and scalable projects.


Author: Pietro Morabito

Editor: Amaury Laporte



  • Ozment, S., DiFrancesco, K., Gartner, T., “Natural Infrastructure in the Nexus”, Nexus Dialogue Synthesis Papers. Gland, Switzerland: IUCN, 2015
  • World Economic Forum, “Water Security: the Water-Food-Energy-Climate nexus”, Island Press, 2011