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With cities being challenged by climate change extremes, a variety of leading cities around the world are implementing blue-green infrastructure solutions to enhance resilience to climate change while restoring the health of ecosystems.

While traditional grey infrastructure systems have, over many decades, proved to be effective in collecting stormwater runoff and draining it from the city, reliance on them has led to numerous unintended negative consequences relating to water quantity and water quality. They include:

Traditional grey infrastructure used to manage stormwater will be challenged by extreme weather caused by climate change. During wet weather events, heavier storms will mean increased amounts of water and wastewater in combined sewer systems for short periods of time. As such, current designs, based on critical ‘design storms’ defined through analysis of historical precipitation data, need to be modified. Meanwhile, during extended periods of dry weather soils dry up and shrink, resulting in the cracking of water mains and sewers, making them vulnerable to infiltration and exfiltration of water and wastewater. A combination of high temperatures, increased pollutant concentrations, longer retention times and sedimentation of solids may lead to corrosion of sewers, shorter asset lifetimes, more drinking water pollution and higher maintenance costs.

Faced with climate change and environmental degradation many cities are turning to Blue-Green Infrastructure (BGI) solutions to enhance climate resilience as well as restore the health of ecosystems. BGI is a strategically planned network of “…natural and semi-natural areas, ranging in size from rain gardens right up to green streets, that are designed and managed to deliver a wide range of environmental, economic, and social benefits including improved water quality”.

A key aspect of BGI is its multifunctionality, specifically, its ability to perform several functions and provide several benefits within the same spatial area. This means BGI harnesses the interrelationships between vegetation and the water cycle to improve living conditions in the city. In turn, this enhances both sustainable development and water- and greenery-related ecosystem services. For example, a green roof can reduce stormwater runoff and the pollution load of the water, while also decreasing the urban heat island effect, improving the insulation of the building and providing a habitat for species. It is important to note that not all green spaces or environmental features qualify as being BGI. In addition to being high quality, they must also form an integral part of an interconnected BGI network and deliver multiple benefits. For instance, an urban park might be considered an integral part of BGI if, in addition to absorbing excess water runoff, it offers recreational opportunities and enhances wildlife.

BGI provides multiple benefits including:

Cities can use fiscal tools to encourage the implementation of BGI practices on both public and private properties as well as new developments and existing developments (retrofits). Fiscal tools are easy to implement and provide decision-makers with the flexibility and creativity to tailor programmes to specific priorities or to geographic areas in a community. This enables a city to focus its resources and programme efforts on a more manageable scale and can provide the opportunity to pilot new incentives to determine the potential for city-wide application. Common fiscal tools include stormwater fees/rates, grants, and rebates and installation finance.

The Los Angeles Department of Water and Power (LADWP) is developing a stormwater incentive programme for the infiltration and on-site use of stormwater from industrial facilities and designing. In addition, the city is designing and constructing ‘green streets’. Under the stormwater incentive programme, all industrial facilities regulated by the Industry General Permit and within LADWP’s service area/areas of interest will be eligible to participate in the program. The total rebate amounts will be based on yield for each respective facility, with the rebate amount of $1,100/acre foot (AF) for infiltration and $1,550/AF for onsite reuse. An example of one green street is the Laurel Canyon Boulevard Green Street Project that will see a series of vegetated infiltration swales and dry wells installed. During storm events, these BGI solutions will capture and treat stormwater runoff from an approximate 123-acre drainage area and infiltrate it into the San Fernando Groundwater Basin. During a normal year, the project will be able to replenish 13 million gallons of rainwater into underground aquifers.

To incentivize BGI retrofits on private property, the city’s Department of Environmental Protection (DEP) will be releasing a Request for Proposals to procure a Program Administrator to launch and administer a new BGI Private Incentive Retrofit Program. The five-year contract will have a value of $43-$58 million with a goal of retrofitting 200 greened acres. DEP has also released a streamlined fast-track review process for private green roof projects funded through its Green Infrastructure Grant Program. The funding schedule sets reimbursement rates for green roof projects based on growing media depth and planted area. These upfront reimbursement rates eliminate uncertainty over how much funding is available for potential projects and by giving this information to applicants in advance. This means DEP can fast-track green roof grant applications, with anticipated design approval within 90 days from the submittal date.

Cities can implement a variety of non-fiscal tools — voluntary mechanisms– to encourage the development of BGI on public and private land including new developments and retrofits. As non-fiscal tools are less intrusive than fiscal tools, they create less resistance from stakeholder groups and allow policymakers to test and refine programmes that may one day develop into mandatory requirements. Common non-fiscal tools include information and awareness campaigns, fast-tracking of BGI project applications by city agencies, pilot and demonstration projects, and leading by example.

Amsterdam is developing various types of BGI at different spatial scales in both existing and new neighborhoods to achieve a variety of benefits including enhanced climate resilience, increased biodiversity, and improved human health. Amsterdam’s BGI will increase the retention and reticulation of rainwater, all the while having a cooling effect on surface temperatures, provide habitats for indigenous plants and animal species, and provide opportunities for recreation and relaxation. The city’s range of BGI being developed includes:

To raise awareness of the issues of stormwater quality and surface runoff, Melbourne Water has developed the Water Smart City Model. This model is an educational activity suitable for all ages which can be used at community events and festivals. The activity involves the audience building a model city with roads and buildings made from Lego building blocks. Food dye, representing pollutants, is placed on the city and rainfall is simulated over the model, carrying the pollution over the impervious surfaces and into the ‘bay’. A variety of features including rain gardens, rainwater tanks, swales and rooftop gardens are then added. Pollution is again added to the model and rain simulated. The amount of surface runoff is significantly decreased due to the retention capabilities of the new features, reducing risks of flooding. Pollution is also captured in the features so the water flowing into the ‘bay’ is cleaner.

BGI not only enhances the resilience of cities to climate change but provides multiple economic, social, and environmental benefits. BGI can be constructed at various spatial scales. BGI is not only about managing too much water but also important in replenishing precious water supplies. A variety of fiscal and non-fiscal tools can be used to enhance the uptake of BGI including grants, fast-tracking of applications, and the educating of the public on the benefits of BGI.

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