Green Infrastructure Evidence Base

Executive summary

Introduction

The value of ‘green infrastructure’ in urban landscapes is becoming increasingly recognised by health professionals, water managers, planners, policy makers and designers around the world. The rapid expansion of towns and cities contains the real risk of creating unliveable, unhealthy environments. The contention is that human habitats need to be healthy and friendly places that use and recycle resources wisely, are clean, safe and accessible, are protected as far as possible from extreme weather conditions, and where natural systems are not only recognised and valued for the critical functions and services they provide, but are assisted in delivering these services.

Green Infrastructure is the network of green places and water systems that delivers multiple environmental, social and economic values and services to urban communities. This network includes parks and reserves, backyards and gardens, waterways and wetlands, streets and transport corridors, pathways and greenways, farms and orchards, squares and plazas, business and institutional green areas, roof gardens and living walls, sports fields and cemeteries.

Green Infrastructure (GI) is critical to the health, liveability and sustainability of urban environments. It strengthens the resilience of towns and cities to respond to the major current and future challenges of growth, health, climate change and biodiversity loss, as well as water, energy and food security. Two key features of Green Infrastructure which distinguish Green Infrastructure from its ‘grey’ counterparts are mutifunctionality and connectivity. Importantly, Green Infrastructure can deliver multiple benefits from the valuable urban space it occupies, compared with single purpose engineering infrastructure. Green Infrastructure also ‘value adds’ by linking and connecting existing green assets, which provides benefits both for people, by enhancing public use opportunities, and for the environment by improving urban ecosystem health and countering habitat fragmentation.

Supporting research

A great deal of research in many parts of the world has firmly established the many and diverse benefits of contact with nature and, inversely, the problems arising from lack of contact with nature. While a wealth of studies focus on human physical and mental health issues, much work has also been done in defining the importance of urban nature in improving temperatures and climatic conditions, water management, economic prosperity, biodiversity and habitat, urban food production and liveability and safety issues.

In 2012 Dr. Martin Ely was commissioned to work with the Green Infrastructure Project to help develop an Evidence Base for Green Infrastructure in South Australia. This study includes a wide ranging literature review with emphasis on the most recent peer reviewed research from around the world. A compelling body of evidence suggests that Green Infrastructure is not only beneficial but essential in the design and development of healthy urban environments.

Ecosystem Services

Healthy ecosystems provide goods and services that are essential to human health and well-being, and therefore underpin GI. Ecosystem concepts apply to cities and towns not just "natural" areas. Ecosystem services include provisioning (food and materials), regulating (moderate environmental conditions and quality), cultural (aesthetic and psychological benefits) and supporting (underlie all ecosystem services) services that apply at a range of scales from the global (such as contributing to the mitigation of climate change) to the local (such as more sustainable management of the local urban water cycle).

Human health and well-being

A large body of research over the last twenty years has investigated the many connections between contact with nature and human health and well-being. Health and well-being are usually defined in the broadest sense to mean not only the absence of disease, but a state of physical, mental and social well-being (World Health Organisation 1946). Research has focused on the three areas of physical health and well-being, psychological health and well-being, and social interaction and community building.

Clear links have been identified between urban greening, physical activity and health, with widespread recognition that physical activity is promoted by ready access to well-managed green spaces and ‘walkable streets'.

The psychological benefits of contact with nature are well-documented, including the ‘restorative’ powers of contact with nature in cities and the general positive emotions engendered by natural settings. Many studies, for instance, confirm the therapeutic power of plants and garden environments in speeding up recovery from injury, surgery and other medical or traumatic events. A wide body of evidence also links animals with human health; documented benefits of pet ownership include lower levels of minor health problems, fewer doctor visits, reduced stress and longer life spans than in people without pets. The ‘biophilia hypothesis’ claims that contact with nature is fundamental to human health because we have an innate need to affiliate with living things. This is further supported by studies on self-regulation of mood and on favourite places, indicating that green settings are preferred as places for restorative experiences such as thinking about problems, recovering focus, forgetting worries, emotional release and relaxation.

Also important are the many enhanced opportunities for social interaction and fostering of community relationships and sense of identity that are facilitated by attractive and welcoming urban green spaces. Such social interaction has been found to be fundamental to human health and well-being.

Green Infrastructure has particular benefits for specific demographic groups, such as older people and children. Access to green space contributes to older people staying active and enhances quality of life through increased physical activity and social interaction. The emerging increase in physical and mental health issues in Australian children has been partly attributed to a decline in physical activity and outdoor play. Writer Richard Louv has coined the term ‘Nature-Deļ¬cit Disorder’ to describe the effects on children of the alienation from nature increasingly prevalent in cities. An emerging and powerful body of evidence shows that contact with nature during childhood can play a significant role in the prevention and management of physical and mental health problems, and improve lifelong well-being.

Community liveability

Green Infrastructure enhances the general attractiveness and ‘liveability’ of urban neighbourhoods. The term ‘community liveability’ covers a range of themes. Some of these are intangible benefits, difficult to quantify, such as cultural or visual and aesthetic values. Research into community liveability is drawn from a wide range of disciplines and looks at a number of issues: cultural and heritage values such as attachments, meanings and symbolism; the visual and aesthetic roles of Green Infrastructure including place making, spatial definition and attractiveness; enhancements to urban amenity such as comfort and safety. Green Infrastructure also provides more easily quantified benefits such as air quality improvement and noise abatement.

Economic prosperity

The monetary value of a number of services and benefits provided by Green Infrastructure are calculable, including the benefits of ecosystem services, amenity values and perceived attractiveness.

Recently developed methods for quantification of net economic values of the ecosystem services provided by Green Infrastructure have led to the quantification of benefits (such as those provided by urban trees) and include air pollution reduction, storm water runoff reduction, and carbon sequestration and storage. The amenity or replacement value of the green asset can also be calculated.

Evidence shows that well-designed Green Infrastructure enhances the economic attractiveness of commercial precincts, increases residential property values, and creates improved opportunities for tourism and economic regeneration.

Potential and significant savings for health care expenditure through increased human physical, mental and social health as a consequence of well-designed and maintained urban green space have been identified in a number of studies.

Climate modification

The modification of urban climates, especially through temperature reduction, is one of the outstanding benefits of Green Infrastructure. A large body of recent research has shown that vegetation and water can assist in mitigating the ‘urban heat island’ effect in cities. The urban heat island refers to a metropolitan area that is significantly warmer than surrounding suburbs or rural areas as a result of urban development including the construction of more buildings and paved surfaces that retain heat. The urban heat island is recognised as a significant contributor to health risks in large cities including increased distress and mortality rates in extreme weather events such as ‘heat waves’, especially among the aged.

Global climate changes in general and recent droughts in particular have further highlighted the need to make better use of Green Infrastructure in the public realm. Plants and water systems play an important role in both climate change mitigation and adaptation. Green Infrastructure assists in reducing temperatures in cities through shading, evapotranspiration and wind speed modification while also providing protection during extreme weather events, reducing water runoff and flooding, and improving air quality.

Water management

Vegetation plays a critical role in the natural water cycle, modifying rainfall inflows, soil infiltration and groundwater recharge, and patterns of surface runoff. Urbanisation has seen the natural water cycle replaced by an artificial ‘urban water cycle’, with extensive impervious surfaces and highly efficient drainage systems, which dramatically increase the quantity, while reducing the quality, of urban storm water runoff. This negatively impacts on ‘receiving’ aquatic ecosystems and also removes a valuable water resource from the city. Green Infrastructure provides efficient and effective contributions, including alternatives, to conventional engineering infrastructure in the process of integrated water cycle management and Water Sensitive Urban Design (WSUD).

Water Sensitive Urban Design now embraces the many ways in which smart and more appropriate water management can contribute to the liveability and resilience of our cities. Along with provision of safe, secure and affordable water supplies, WSUD supports green landscapes that significantly enhance urban amenity, help to cool urban environments, improve the health of waterways and provide opportunities for active and passive recreation.

Urban ecology

In an historical sense, nature and the city have been seen as separate and ‘mutually exclusive’. An urban ecology approach, however, sees people, nature and the city as part of the same ‘urban ecosystem’. Healthy biodiversity plays a fundamental role in the functioning of ecosystems and their ability to deliver long-term ecosystem services, with biodiversity loss an issue of increasing global concern. Nature and biodiversity in cities contribute to our human sense of place, identity and psychological well-being. Green Infrastructure supports biodiversity by creating or conserving habitat patches linked by corridors, thereby reducing habitat fragmentation. While the ‘urban nature’ found in cities may be different from ‘wild nature’, it still contributes to healthy ecosystem function and has both intrinsic and human well-being values.

Food production

The quest for food security along with the health imperative to eat well and be active increasingly brings the subject of ‘food’ into focus in towns and cities. Green Infrastructure and urban food are intimately related through the perceived needs to retain productive agricultural land on the urban fringe and to integrate food production into urban areas. Methods of urban food production are many and varied, ranging from private and school kitchen gardens to verge gardens and urban farms, and result in a wide range of health and well-being outcomes.

Community gardens have received particular attention for their multifunctional role in providing access to healthy food options, physical activity, social interaction and the fostering of community relationships.

Green Infrastructure guiding principles

To design, establish and maintain Green Infrastructure necessitates, in many cases, a new way of thinking about urban environments. To achieve the many potential benefits of Green Infrastructure it must be embraced as an integral element of the urban landscape. Government, industry and community sectors require a thorough understanding of the benefits as well as a robust capacity for design, development and maintenance. Planning and investment in Green Infrastructure need to be guided by principles that reflect and ensure a full acceptance of the concept.

We suggest that successful Green Infrastructure is underpinned by the following five principles:

  • Integration: Green infrastructure is fundamental to urban planning and design frameworks for both new growth areas and redevelopments.
  • Nature-based: Green Infrastructure utilises natural processes to provide essential services and functions that improve the quality of urban water, air, soil, climate and wildlife habitat.
  • Collaboration: The design, development and maintenance of Green Infrastructure require open and on-going collaboration between government, industry and communities.
  • Evidence: Green Infrastructure policy, planning and design are grounded in science and the lessons of experience, and are informed by emerging practices and technologies.
  • Capacity: Green Infrastructure requires commitment to building motivation, knowledge, skills and access to resources.