LONDON’S GLOBAL UNIVERSITY Green Infrastructure for London: A review of the evidence A report by the Engineering Exchange for Just Space and the London Sustainability Exchange. Authors: Alison Fairbrass, Kate Jones, Aimee McIntosh, Zeyu Yao, Liora Malki-Epshtein, Sarah Bell 19 February 2018 Supported by the Natural Environment Research Council A public engagement pilot project Abstract Green infrastructure is a strategic, planned network of natural, semi-natural and artificial features and networks designed and managed to deliver a wide range of ecosystem services and quality of life benefits (European Commission, 2016; European Commission, 2012; Tzoulas et al., 2007; Bowen & Parry, 2015). In an urban setting, green infrastructure networks may include traditional parks, woodlands, wetlands, rivers, private gardens, street trees, allotments, playing fields, cemeteries and newer innovations such as green roofs and sustainable drainage systems (SuDS) (GLA, 2015a; Wilebore & Wentworth, 2013). This report reviews the benefits, costs and risks of green infrastructure for air quality, surface water management, biodiversity and human health and wellbeing in London. Green infrastructure can improve air quality by providing barriers to sources of pollution such as busy roads. Plants also remove pollution from the air. Surface water management that aims to reduce local flood risk and water pollution can benefit from green infrastructure which slows down runoff, captures pollutants and increases the amount of water soaking into the ground instead of running into drains. Increasing habitat and connectivity of green spaces in London can encourage greater abundance and diversity of species. A diversity of planting encourages invertebrate diversity, which provides a food source for animals such as birds and bats. Access to green spaces has been demonstrated to improve human physical and mental health. Physical activity may be higher in areas with access to good quality green space. Exposure to nature and a green environment reduces anxiety and improves mental ill-health. Green spaces and infrastructure may also be associated with improved wellbeing, lower crime rates and a stronger sense of place, but this needs to be considered in a social context. ‘Green gentrification’ can benefit wealthier, able-bodied residents to the detriment of more vulnerable groups. Evaluating the costs and benefits of green infrastructure is complicated by its multi-functional nature. The costs of green infrastructure need to be considered on a project-by-project basis. It is difficult to assign costs to specific services or benefits provided by a green infrastructure component. In addition to economic costs for installation and maintenance there may be other dis-benefits that need to be accounted for and managed. Trees and plants may have negative impacts due to pollen dispersal and emission of volatile organic compounds and ozone which can contribute to air pollution. Tree roots and branches may also damage roads and pavements, and leaves require sweeping. Insects, birds and other species can contribute to increasing the cost of pest control and cleaning. Not all green infrastructure components are suitable in all conditions. More detailed monitoring of air pollution, biodiversity and surface water is needed to support better prediction of environmental quality and the impact of green infrastructure. There is a risk that green infrastructure components may be implemented inappropriately, undermining benefits and increasing costs and likelihood of failure. There is also the risk that, unless green infrastructure is well integrated into the urban environment, it can become a space that is visited for a specific activity, rather than being used and experienced on a daily basis. There are concerns that infrequent use of green space may reduce its capacity to provide health and wellbeing benefits and limit social cohesion (GLA, 2015a). Green infrastructure provides considerable benefits to London, and better integration and connection within the city could further enhance London’s ability to respond to these problems. Accounting for the costs and risks associated with green infrastructure, and addressing the need to strengthen the evidence base about its function and impacts alongside its benefits, will allow for more robust decision making and adaptive approaches to planning and management. Green Infrastructure for London 1 Table of Contents Abstract ................................................................................1 4. Health and Wellbeing ....................................................33 What is the problem? ......................................................33 Introduction ..........................................................................3 Physical health ...........................................................33 1. Air Quality .........................................................................7 Mental health ..............................................................33 How can green infrastructure help? .................................34 What is the problem? ........................................................7 Physical health ...........................................................34 Street canyons and air quality.......................................8 Mental health ..............................................................35 How can green infrastructure help? ...................................9 Social wellbeing ..........................................................35 Airflow and pollution dispersion ....................................9 Built environment aesthetics .......................................36 Pollution deposition and absorption by plants ............10 Local food production ................................................36 Urban cooling .............................................................11 Skills and employment ...............................................37 Costs ..............................................................................12 Nature tourism and leisure activities............................37 Risks ...............................................................................12 Human health and wellbeing ......................................37 2. Water ...............................................................................15 Costs ..............................................................................38 What is the problem? ......................................................15 Risks ...............................................................................38 How can green infrastructure help? .................................16 5. Design and Management ...............................................43 Green roofs and walls .................................................17 Design .............................................................................43 Rainwater harvesting ..................................................18 Vegetation structure ...................................................43 Infiltration systems ......................................................18 Scale ..........................................................................43 Permeable surfaces ....................................................19 Character ...................................................................43 Filter strips and drains ................................................19 Management ..............................................................43 Bio-retention systems ................................................20 Strategic actors ..........................................................44 Detention basins ........................................................20 Long-term management.............................................44 Swales .......................................................................20 Costs ..............................................................................20 Conclusions ........................................................................45 Financial costs ............................................................20 What is the problem? ......................................................45 Opportunity costs .......................................................21 How can green infrastructure help? ............................45 Risks ...............................................................................21 Costs ..............................................................................45 3. Biodiversity .....................................................................25 Risks ...............................................................................45 Green infrastructure for London ..................................46 What is the problem? ......................................................25 How can green infrastructure help? .................................25 References ..........................................................................48 Semi-natural green spaces ........................................26 Parks and commons ..................................................26 Domestic gardens .....................................................26 Urban waterways ......................................................27 Green roofs and walls ................................................27 Grass verges ..............................................................28 Artificial structures ......................................................28