The purpose of green infrastructure (or urban green infrastructure, UGI) is to leverage natural or semi-natural systems and processes to address complex societal and urban challenges, particularly those exacerbated by climate change and rapid urbanization, while simultaneously providing human well-being and biodiversity benefits.
Green infrastructure is considered a Nature-Based Solution (NBS) for resilience.
Primary Purposes and Functions of Green Infrastructure
Green infrastructure goes "beyond aesthetics" to serve multifaceted, practical purposes in urban environments. Its core purpose is encapsulated in three interconnected domains: climate resilience, environmental quality, and social/economic benefits.
1. Enhancing Climate Resilience (Adaptation and Mitigation)
The primary purpose of green infrastructure is to help cities adapt to and mitigate the impacts of climate change, especially extreme urban heat and flooding.
• Mitigating Urban Heat Island (UHI) Effect and Thermal Extremes: Green infrastructure is vital for cooling cities, which tend to be significantly warmer than surrounding rural areas due to the UHI effect.
◦ Providing Cooling and Shade: Urban forests and trees provide shade, reducing surface temperatures, and cooling the air through evapotranspiration (the process of water movement through a plant and its evaporation). Greenery can reduce surface temperatures by up to
C.
◦ Reducing Energy Consumption for Cooling: By mitigating heat, green roofs and vegetation reduce the demand for mechanical cooling, leading to lower energy consumption and cost savings for end-users.
◦ Reducing Risk from Extreme Events: Green/natural and blue infrastructure can reduce energy use and the risk from extreme events like heatwaves, flooding, heavy precipitation, and droughts.
• Stormwater Management and Flood Prevention: Green infrastructure mimics natural processes to manage excess water, mitigating the effects of increased impervious surfaces that exacerbate stormwater runoff and flooding.
◦ Filtering and Absorbing Runoff: Elements like permeable pavements, rain gardens, and bioswales allow rainwater to infiltrate the ground, reducing the volume and speed of runoff, lessening the risk of flooding, and aiding groundwater recharge.
◦ Flood Control: Wetlands and riparian buffers provide natural flood control. Ecosystem-based Adaptation (EbA) approaches, such as urban greening and restoration of wetlands, have been effective in reducing flood risks.
• Carbon Mitigation: Increasing urban green space enhances a city's capacity for carbon sequestration by absorbing carbon dioxide (GHG emissions) through photosynthesis, contributing to global climate change mitigation. Urban green infrastructure is also listed as a technically viable mitigation option.
2. Improving Environmental Quality
Green infrastructure serves to maintain and improve the health of urban ecosystems and natural resources.
• Air Quality Enhancement: Trees and other vegetation act as natural air filters, absorbing pollutants such as nitrogen dioxide, sulfur dioxide, and particulate matter, leading to healthier respiratory environments.
• Water Quality Protection: Green elements like rain gardens and wetlands act as natural filters, removing sediments, nutrients, and other contaminants from stormwater runoff before it reaches waterways.
• Supporting Biodiversity and Ecosystem Health: Green spaces create and connect habitats, providing refuge and resources for wildlife. Green corridors are vital as they connect fragmented green spaces, allowing for wildlife movement and promoting ecosystem resilience and biodiversity. Green infrastructure also supports pollinator health, which is crucial for local ecosystems and food security.
3. Delivering Social and Economic Benefits
Green infrastructure contributes directly to human welfare, social cohesion, and urban economic vitality.
• Enhancing Well-being and Public Health: Green spaces provide opportunities for recreation and relaxation, reducing stress levels, improving mood, and yielding better mental and physical health outcomes for urban residents. It also reduces heat-related morbidity and mortality.
• Fostering Social Cohesion: Green spaces serve as gathering places that foster social interaction and a sense of belonging, strengthening community bonds and social capital.
• Boosting Economic Vitality: Investing in green infrastructure creates job opportunities in design, construction, and maintenance, supporting the growth of the green economy. Properties located near green spaces often have ** higher values**.
In summary, the purpose of green infrastructure is to move beyond the limitations of purely traditional ("grey") infrastructure by using multi-functional, nature-based solutions to build comprehensive urban heat resilience.
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