Regulating urban surface runoff through nature-based solutions – An assessment at the micro-scale. Zölch,T, Henze, L, Keilholz, P & Pauleit, S. Environmental Research, Volume 157, August 2017, Pages 135–14.
- Runoff after heavy rain events accounts for approx. 95% of total precipitation in highly sealed urban areas.
- By enhancing water storage capacities green infrastructure reduces runoff by max. 14.8% compared to the baseline.
- Green roofs and trees both show to be effective but due to different functions.
- The reduction of runoff is larger with higher shares of green cover in the case area.
Urban development leads to changes of surface cover that disrupt the hydrological cycle in cities. In particular, impermeable surfaces and the removal of vegetation reduce the ability to intercept, store and infiltrate rainwater. Consequently, the volume of stormwater runoff and the risk of local flooding rises. This is further amplified by the anticipated effects of climate change leading to an increased frequency and intensity of heavy rain events. Hence, urban adaptation strategies are required to mitigate those impacts.
A nature-based solution, more and more promoted in politics and academia, is urban green infrastructure as it contributes to the resilience of urban ecosystems by providing services to maintain or restore hydrological functions. However, this poses a challenge to urban planners in deciding upon effective adaptation measures as they often lack information on the performance of green infrastructure to moderate surface runoff. It remains unclear what type of green infrastructure (e.g. trees, green roofs), offers the highest potential to reduce discharge volumes and to what extent.
Against this background, this study provides an approach to gather quantitative evidence on green infrastructure’s regulation potential. We use a micro-scale scenario modelling approach of different variations of green cover under current and future climatic conditions. The scenarios are modelled with MIKE SHE, an integrated hydrological modelling system for building and simulating surface water and groundwater flow, and applied to a high density residential area of perimeter blocks in Munich, Germany. The results reveal that both trees and green roofs increase water storage capacities and hence reduce surface runoff, although the main contribution of trees lies in increasing interception and evapotranspiration, whereas green roofs allow for more retention through water storage in their substrate. With increasing precipitation intensities as projected under climate change their regulating potential decreases due to limited water storage capacities. The performance of both types stays limited to a maximum reduction of 2.4% compared to the baseline scenario, unless the coverage of vegetation and permeable surfaces is significantly increased as a 14.8% reduction is achieved by greening all roof surfaces.
The authors conclude that the study provides empirical support for the effectiveness of urban green infrastructure as nature-based solution to stormwater regulation and assists planners and operators of sewage systems in selecting the most effective measures for implementation and estimation of their effects.
Urban green infrastructure as nature-based solution to regulate surface runoff becomes increasingly important, as climate change and urbanisation alter the urban water balance. The present study assessed the performance of two urban green infrastructure (UGI) types, trees and green roofs, on relevant hydrological processes, especially surface runoff. The two measures were applied in scenarios of different greening quantity and for heavy rain events of different intensities as projected for the future. This scenario approach revealed that both trees and green roofs contribute positively by interception, evapotranspiration and infiltration. Differences in their performance showed to be dependent on the greening quantity, share of permeable surfaces leaf area index (LAI) and finally, intensity of the rainfall event. Generally, their effectiveness remains low under heavy rain events, unless a significant proportion of the case area is greened to provide sufficient water storage capacities (Artmann, 2014).
For urban planning the presented results have practical implications for the selection of UGI types to reduce surface runoff volumes and in consequence reduce discharge loads, the sewage system has to handle. An effective nature-based solution increases the storage capacities within the area of interest as much as possible, while using open spaces that have not been used previously and/or while providing benefits to other areas of urban planning. Trees increase the storage capacity mainly by intercepting and evapotranspiring rainwater, their infiltration capacity is limited to the tree pits. But trees can normally not be implemented in large quantity in dense urban areas due to their requirements of open space. Green roofs on the other hand, provide storage capacity mainly by retaining rainwater in their substrates and can be implemented at larger scale on previously unused roof surfaces.
Furthermore, both types are multifunctional and can provide co-benefits for urban planning. The approach represents a first step in allowing planners as well as operators of sewage systems to estimate reductions in runoff volume when locally implementing UGI measures. These estimations could be further improved by integrating additional stormwater management practices and the drainage system in more detail into the modelling setup. Thus, conducting a larger systematic study of UGI scenarios would allow for including e.g. more UGI types, different species and LAI values as well as planting conditions. Such a study could enhance the provision of empirical evidence for climate resilient urban planning.
In March 2013 the Landscape Institute published an updated Mission Statement, ‘Green Infrastructure: An integrated approach to land management’. The document was described as,
“An opportunity to showcase a range of successful strategic GI work and completed
projects. The aim is to give public and private sector bodies, clients and natural and built environment professionals fresh insights into the benefits GI can bring by creating multifunctional landscapes and show how people can collaborate to deliver it.”
Following our recent post discussing the new report launched by Arup, Cities Alive: Towards a walking world, further research to support links between good urban design and well-being has been published in The Lancet – see reference link below. The Arup report, is a collaboration between Arup’s Foresight + Research + Innovation, Transport Consulting and Urban Design teams, and discusses the benefits of walkable cities – economic, social, environmental and political, setin out measures for improving walkability.
Abstract: Urban design can promote walking: people physically active for up to 1.5 hours more per week in activity-friendly neighbourhoods
Source: Sallis, J.F., Cerin, E., Conway, T.L., Adams, M.A., Frank, L.D., Pratt, M., Salvo, D., Schipperijn, J., Smith, G., Cain, K.L., Davey, R., Kerr, J., Lai, P.-C., Mitáš, J., Reis, R., Sarmiento, O.L., Schofield, G., Troelsen, J., Van Dyck, D., De Bourdeaudhuij, I. & Owen, N. (2016). Physical activity in relation to urban environments in 14 cities worldwide: a cross-sectional study. The Lancet. DOI: 10.1016/S0140-6736(15)01284-2. This study is available at: http://www.ipenproject.org/documents/IPEN-Research-Brief%20Lancet%20paper%2004-16.pdf
People who live in the most ‘activity-friendly’ neighbourhoods do up to 1.5 hours more physical activity a week than those in the least supportive neighbourhoods. This is according to a new international study which measured levels of exercise — mainly walking for recreation or transport — in relation to the urban environment across 14 diverse cities. The results show how urban design — such as parks and local amenities — can promote healthy lifestyles which also bring environmental benefits, such as better air quality, through reduced car use.
Globally, physical inactivity is responsible for 5 million deaths per year through its effects on diseases such as diabetes, heart disease and some cancers1. It is known that people who live in very ‘walkable’ neighbourhoods tend to be more physically active than those in less walkable areas. The WHO thus recommends improving the urban environment to support ‘active transport’ (walking and cycling) and recreation in its Global Strategy on Diet, Physical Activity and Health.
This study further explores the link between the urban environment and exercise by providing objective data on activity levels in a diverse range of cities. Data were used from 6 822 participants in the study who wore accelerometers around their waist for 4–7 days. Accelerometers assess vertical movement of the body and mainly detect walking. Participants lived in one of 14 cities across 10 countries (Belgium, Brazil, Colombia, the Czech Republic, Denmark, China (Hong Kong), Mexico, New Zealand, the UK and the USA).
The researchers related activity levels to urban features which are thought to affect walkability found in a 0.5 km and a 1 km zone around each participant’s home. Six features were considered: number of residential dwellings; number of street junctions (accessible to pedestrians); mixture of land use (indicating easy access to retail areas and public buildings); number of bus, rail or ferry stops/stations; distance to nearest public transport stop/station; and number of parks.
Average activity levels varied greatly by neighbourhood. Participants with the most activity-supportive environmental features within 1 km of their home did up to 89 minutes more physical activity a week, on average, than those in 1 km zones with the fewest activity-supportive features. For 0.5 km zones, the difference in activity levels was 68 minutes. On average, participants across all 14 cities did 37 minutes of physical activity per day. Baltimore, USA, had the lowest average rate of activity (29.2 minutes per day) and Wellington, New Zealand, had the highest (50.1 minutes per day).
Three urban features were strongly associated with higher activity levels:
- High residential density. This is needed to support important components of a walkable neighbourhood, such as local shops and a frequent public transport service.
- High density of public transport stops. Interestingly, distance to the nearest transport stop was not associated with activity levels. Instead, the researchers suggest that a high number of transport options is more likely to meet residents’ needs and thus increase the likelihood of walking to a stop. Good access to public transport is necessary for a less car-dependent lifestyle, they state.
- Parks. These are not just locations for recreation in themselves, but destinations that people choose to walk to.
Studies usually associate mixed land use with physical activity, but not in this case. However, the researchers say this may be due to limitations of their method; for example, they did not map unregistered shops, such as informal markets, which are common in middle-income countries. Street-junction density, which indicates connectivity, showed some influence on walking levels, but results on this feature were mixed.
Importantly, the links between built environment and physical activity were generally similar across all the cities. This suggests that improving urban design is a solution that applies everywhere.
The study recommends that decision makers in the public health, environmental, transport and park sectors work together to promote physical activity as way of cutting air pollution and greenhouse gas emissions and energy usage, whilst achieving health benefits.
- Lee, I.M., Shiroma E.J., Lobelo F., Puska P., Blair S.N., & Katzmarzyk P.T. (2012). Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet, 380: 219–99.
Characteristics that promote creativity and innovation
The paper discusses urban design and sustainability assessment methods plus characteristics that promote creativity and innovation. Eight key characteristics that promote creativity and innovation in urban design were identified:
risk-taking in idea generation
team understanding and commitment
clear, and ideally visionary, brief and strategy
access to relevant information and appropriate and sufficient resources
ownership of ideas
good communication skills, including visualisation and diplomatic skills
working well with stakeholders outside the design team
The interviews with UK built environment professionals on the relationship between sustainability assessment methods and creativity and innovation in urban design confirm many of the core findings within urban sustainability research. The authors have established that sustainability assessment methods do impact creativity and innovation in urban design, and that many current methods are described more negatively than positively in terms of their impact upon creativity and innovation.
There also was broad recognition of the value that sustainability assessment methods have in elucidating sustainability issues and in providing guidance on how they might be addressed. This, in turn, provides a platform from which urban designers can be creative and innovative, both at specific points in the urban design process and throughout the process. Based on the above findings, the authors propose the following principle: a sustainability assessment method will promote creativity and innovation in urban design if it engages competently with sustainability, works at a scale that allows for breadth and depth (typically greater than the building scale), and incorporates a set of eight key characteristics designed to promote creativity and innovation. This principle should guide any new sustainability assessment methods under development.
The findings also suggest that the people creating sustainability assessment methods should think more broadly about those who will use their methods and for what purpose(s). At the moment, many methods appear to be designed to work within a more deterministic, normative, empirical and scientific framework. They either fail to understand or ignore the creative and innovative aspects of urban design and the designers who use them (and who work in a more ‘designerly’ way) (Cross, 1982). Perhaps, when sustainability is more embedded in society, sustainability assessment will naturally encourage creative processes as well as creative and sustainable design solutions.
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The UK’s Department for Communities and Local Government has recently published revised green infrastructure guidance as part of the National Planning Practice Guide (PPG). Green infrastructure now has its own section under ‘Natural Environment’ (along with landscape, biodiversity and ecosystems and brownfield land). It provides a definition of green infrastructure and describes its value to delivering sustainable development and planning policies, including building a strong, competitive economy and delivering a wide choice of high quality homes.
What is green infrastructure?
Green infrastructure is a network of multifunctional green space, urban and rural, which is capable of delivering a wide range of environmental and quality of life benefits for local communities.
Green infrastructure is not simply an alternative description for conventional open space. As a network it includes parks, open spaces, playing fields, woodlands, but also street trees, allotments and private gardens. It can also include streams, canals and other water bodies and features such as green roofs and walls.
Why is green infrastructure important to delivering sustainable development?
Green infrastructure is important to the delivery of high quality sustainable development, alongside other forms of infrastructure such as transport, energy, waste and water. Green infrastructure provides multiple benefits, notably ecosystem services, at a range of scales, derived from natural systems and processes, for the individual, for society, the economy and the environment. To ensure that these benefits are delivered, green infrastructure must be well planned, designed and maintained. Green infrastructure should, therefore, be a key consideration in both local plans and planning decisions where relevant.
What is a strategic approach to green infrastructure?
To assist in planning positively for green infrastructure local planning authorities may wish to prepare an authority-wide green infrastructure framework or strategy. This should be evidence-based by, for example, including an assessment of current green infrastructure provision that identifies gaps in the network and the components and opportunities for improvement. The assessment can inform the role of green infrastructure in local and neighbourhood plans, infrastructure delivery plans and Community Infrastructure Levy (CIL) schedules.
Local Plans should identify the strategic location of existing and proposed green infrastructure networks. Where appropriate, supplementary planning documents can set out how the planning, design and management components of the green infrastructure strategy for the area will be delivered.
This strategic approach to green infrastructure may cross administrative boundaries. Therefore neighbouring authorities, working collaboratively with other stakeholders including Local Nature Partnerships (LNPs) and Local Enterprise Partnerships (LEPs), may wish to consider how wider strategies for their areas can help address cross-boundary issues and help meet the Duty to Cooperate.
How can green infrastructure help to deliver wider planning policy?
Green infrastructure can help to deliver a variety of planning policies including:
Building a strong, competitive economy
Green infrastructure can drive economic growth and regeneration, helping to create high quality environments which are attractive to businesses and investors.
Delivering a wide choice of high quality homes
Green infrastructure can help deliver quality of life and provide opportunities for recreation, social interaction and play in new and existing neighbourhoods. More broadly, green infrastructure exists within a wider landscape context and can reinforce and enhance local landscape character, contributing to a sense of place. Green infrastructure is also an important approach to delivering ecosystem services and ecological networks.
Requiring good design
Well-designed green infrastructure helps create a sense of place by responding to, and enhancing, local landscape character. Green infrastructure can also help create safe and accessible environments in new development and the regeneration of brownfield sites in existing built up areas.
Promoting healthy communities
Green infrastructure can improve public health and community wellbeing by improving environmental quality, providing opportunities for recreation and exercise and delivering mental and physical health benefits. Green infrastructure also helps reduce air pollution, noise and the impacts of extreme heat and extreme rainfall events.
Meeting the challenge of climate change, flooding and coastal change
Green infrastructure can help urban, rural and coastal communities mitigate the risks associated with climate change and adapt to its impacts by storing carbon; improving drainage (including the use of sustainable drainage systems) and managing flooding and water resources; improving water quality; reducing the urban heat-island effect and; where appropriate, supporting adaptive management in coastal areas. Green infrastructure networks also help species adapt to climate change by providing opportunities for movement.
Conserving and enhancing the natural environment
The components of green infrastructure exist within the wider landscape context and should enhance local landscape character and contribute to place-making. High quality networks of multifunctional green infrastructure provide a range of ecosystem services and can make a significant contribution to halting the decline in biodiversity.
How should green infrastructure be planned for in the long term?
As with other forms of infrastructure, green infrastructure requires sustainable management and maintenance arrangements to be in place if it is to provide benefits and services in the long term. Arrangements for managing green infrastructure, and for funding its management over the long-term, should be identified as early as possible when planning green infrastructure and factored into the way that it is designed and implemented.
How should green infrastructure be considered in planning decisions?
Where appropriate, planning proposals should incorporate green infrastructure in line with local and neighbourhood plan policies and site specific considerations. As a component of sustainable development, green infrastructure should be considered at an early stage of a planning proposal. Depending on individual circumstances, planning obligations, conditions or the Community Infrastructure Levy may all be potential mechanisms for securing and funding green infrastructure.