The construction and maintenance of infrastructure is one of a municipality’s largest expenses. It is estimated that about 3.8 percent of global GDP ($3.3 trillion per year) needs to be invested into infrastructure O&M. In comparison to grey infrastructure, Green Infrastructure (GI) can be a low-cost, low-maintenance and low-carbon emission alternative that allows cities to build resilience and safeguard their social and economic assets.
CONSTRUCTION AND O&M COST REDUCTION BENEFITS
One cost-benefit analysis of GI in the United States found that when compared with grey infrastructure, GI initiatives generally had reduced built capital (e.g., equipment, installation) costs, reduced land acquisition costs, reduced external costs (i.e., off-site costs imposed on others), reduced operation costs, and reduced repair, maintenance and replacement costs. The majority of municipalities surveyed in the US and Canada (85%) stated that GI either reduced costs or was comparable in costs to grey infrastructure.
A CBA conducted as part of the storm management plan for the City of Philadelphia found that the benefits of GI for stormwater control ranged from $1.94 billion to $4.45 billion, while grey infrastructure benefits ranged from only $0.06 billion to $0.14 billion over a 40-year period (Stratus Consulting 2009). The City of Philadelphia, through the same plan, converted two square miles to GI and estimates it has saved the city $340 million (US EPA 2010).
A life cycle assessment (LCA) is a useful exercise to evaluate all costs (e.g., construction, O&M and disposal) of a specific GI intervention, providing a basis for the comparison of different green and grey infrastructure.
While initial capitalization costs vary and, in some cases, can be higher than those of grey infrastructure, GI can provide similar levels of environmental or climate risk reduction with lower O&M costs and life cycle cost over time compared to grey infrastructure. For instance, parking lots constructed with permeable pavement, despite having higher initial capital costs, can have significantly lower maintenance costs compared with traditional asphalt. Restoring and conserving wetlands, floodplains, shorelines and other natural systems can be less costly than building and maintaining concrete and steel structures (The Nature Conservancy 2014). While grey infrastructure depreciates over time, functions provided by well-maintained GI are likely to increase over time.
ENERGY EFFICIENCY BENEFITS
GI also provides cost savings via greater energy efficiency. Increasing shade, extra insulation in buildings, and reducing the energy needed to treat stormwater all results in lower municipal costs.
Green roofs increase building energy efficiency by lowering absorption of solar radiation and thermal conductance, thus lowering electrical costs. The green roof on the Target Center Arena in Minneapolis covers 113,000 square feet and has cut annual energy costs by $300,000. The Center for Sustainable Systems estimated that if commercial developers in the United States installed green roofs on the approximately 40 billion square feet of buildings being constructed between 2003 and 2035, property owners could save $95 billion in avoided heating, cooling and roof replacement costs.
Pumping and treating wastewater are energy-intensive processes; for municipal governments, drinking water and wastewater plants are typically the largest energy consumers, often accounting for 30–40 percent of total energy consumed (US EPA 2018). GI interventions that capture precipitation and manage it locally through natural processes can help reduce the energy needed. For example, green roofs, swales, retention ponds and rainwater harvesting can prevent stormwater from reaching the sewerage system, reducing the amount of water that needs treatment. These methods also assist with recharging local groundwater supplies that could reduce the need to transport water from distant sources.
Source: Engaging the Private Sector in Green Infrastructure Development and Financing: A Pathway Toward Building Urban Climate Resilience (Chemonics International Inc. for USAID and ATLAS), October 2018
Toni Pogue
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