People living in neighbourhoods without much greenspace

 

Credit: JRF/Tim Smith

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On this page:

 

• Introduction
• How green infrastructure can regulate the local environment
• Heatwaves and green infrastructure
• Flooding and green infrastructure

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Introduction

 

People living in neighbourhoods with very little greenspace, especially in urban areas, may experience more extreme impacts from events like flooding and heat-waves. 'Green infrastructure' provides a way to improve local neighbourhood environments and better regulate climate change and extreme weather impacts. 
 

The impacts of climate change and extreme weather events can affect anyone, but people living in certain types of neighbourhoods have the potential for more serious harm. Neighbourhoods which are more built up than others are more likely to be associated with higher temperatures, especially during heat waves¹.  They can also be associated with higher rates of runoff from extreme rainfall, although this is also affected by other factors such as drainage infrastructure and topographic characteristics².
 

 

How green infrastructure can regulate the local environment

 

‘Green infrastructure’ can be used to increase community resilience to a range of climate-related impacts and provide wider benefits for human health and wellbeing. It can be comprised of natural or semi-natural areas of vegetation, water bodies and other non built-up land and can exist as managed or unmanaged, public or private and small or large zones³,⁴. Therefore components of green infrastructure can include gardens, green walls and roofs, trees, shrubs and hedges through to parks, allotments, ponds, woodlands, fields, lakes, canals and rivers. Together they provide “an interconnected network of green space that conserves natural ecosystem values and functions and provides associated benefits to human populations”⁵. Benefits are often thought of as ‘ecosystem services’: including the supply of food and fuel (provisioning services); flood, temperature and erosion control (regulating services); opportunities for recreation and relaxation (social/cultural services) and areas for biodiversity (supporting services)⁶. The importance of these services for health and wellbeing, sustainability and climate resilience is recognised by central government through its national ecosystem services assessments and associated programme of activities, tools and recommendations^7,8.

 

This section shows how elements of green infrastructure can help to regulate local neighbourhood environments and therefore reduce people’s exposure to climate impacts and related extreme weather. It particularly centres on providing evidence about how urban green spaces (which can include related ‘blue’ space) help to modify high temperatures and the characteristics of surface water runoff.

 

The regulating services provided by green spaces are particularly valuable for adaptation in towns and cities given that this is where such services are often lacking and where most people live. Although this section centres on one set of functions, it should be remembered that green infrastructure is multi-functional. It provides a role in climate mitigation (carbon storage and sequestration), supports biodiversity and has wider health and wellbeing impacts which influence community resilience ^9,10 including:

• Regulating other environmental processes, such as air, water and noise pollution which in turn has financial benefits¹¹.
• Encouraging and providing space for exercise since people are 24% more likely to meet recommended standards of physical exercise if they live within 500m of accessible green space¹².
• Helping to support psychological wellbeing, education and child development¹³.
• Providing spaces for social interaction and improving neighbourhood cohesion¹⁴.

 

The tendency of some neighbourhoods to increase the exposure of people to climate impacts can be compounded by other personal, environmental and social factors which make their residents particularly vulnerable. These include personal factors associated with sensitivity (e.g. due to age or poor health), factors associated with building characteristics (e.g. living in high rise buildings or buildings with basement accommodation) and social factors associated with adaptive capacity, including being on a low income, being socially isolated or being a tenant. People experiencing multiple causes of vulnerability are the most extremely socially vulnerable. See also Which places are disadvantaged?

 

 

Heatwaves and green infrastructure

 

Cities are prone to the 'Urban Heat Island' (UHI) effect, meaning that temperatures in cities are generally higher than in the rural areas which surround them^15,16.  The extent of these differences varies with weather conditions, season and time of day, often being most marked during the night-time and sometimes not been shown at all. During heatwave events, temperatures in city centres can be particularly high since the weather conditions associated with such events – e.g.  low wind speeds and cloud-free conditions – also favour the development of the UHI effect. During the August 2003 heat-wave, a night-time UHI intensity of up to 9 degrees C was recorded in London¹⁷.  During 2010, air temperature measurements showed that Manchester’s daytime UHI was most commonly around 1 degrees C in both summer and winter, increasing to 1.5 degrees C during summer nights¹⁸. Extreme UHI intensities of up to 8 degrees C were recorded during some summer nights with even greater values during winter nights¹⁹, when the UHI effect generally provides benefits for people living in urban areas.

 

The UHI benefits urban residents in winter but can make people more likely to experience heat-related stress and discomfort in summer. Climate projections for the 2050s suggest that average summer night-time temperatures will be around 2-3 degrees C higher than today (based on the central estimate of the medium emissions scenario relative to 1961-90)²⁰. This temperature increase will be felt most acutely in urban areas.

 

Heat-wave thresholds (Table 1) used to issue warnings and guidance to organisations and the wider public differ across the UK in recognition of the different temperatures which people are used to as a result of where they live in the country. However, they do not account for differences between urban and rural areas, except in London, by virtue of London having its own threshold value.

 

Region	Day max (°C)	Night min (°C)
North East England	28	15
North West England	30	15
Yorkshire and the Humber	29	15
West Midlands	30	15
East Midlands	30	15
East of England	30	15
Southeast England	31	16
London	32	18
Southwest England	30	15
Wales	30	15

Table 1: Heat-wave thresholds used as part of the Heat-Health Watch system which runs from 1^st June to 15^h September each year. Temperatures must be forecast to exceed thresholds on at least 2 consecutive days to trigger warnings²¹.

 

Green infrastructure has a cooling effect and helps to modify temperatures and the Urban Heat Island effect. For example, urban parks have been shown to be on average 1°C cooler than built-up areas and larger parks have a greater cooling effect²². The cooling effect can occur over considerable distances and be pronounced during the night-time when heatwaves can be particularly problematic. Measurements taken around Kensington Gardens (London) showed temperature reductions of up to 4°C and a cooling effect being felt up to distances of around 400m²³.  However, interventions on smaller scales and in different forms – such as green roofs and street trees – can also have a local impact and are an important part of green infrastructure planning especially since many urban areas have limited opportunities to establish new green spaces^24,25. The most effective measures include trees planted over grass, as long as grass is well watered²⁶. Various evidence reviews and practitioner summaries, are available, for example:

• Academic literature reviews ⁹, ¹¹,²⁷
• Evidence and policy summaries for particular urban areas^10,28,29
• National or generic guidance^12,32,33

Green infrastructure also helps to cool temperatures within buildings and reduces the demand for air conditioning, helping to meet wider mitigation policy goals. Neighbourhood green spaces like parks and street trees help to reduce peak summer temperatures over a broad geographical area and therefore also within buildings. Vegetation directly on or near a building also affects internal temperatures including through shading and, in the case of green roofs, through insulation. In summer, this reduces the demand for cooling energy and therefore carbon emissions and lowers the operating costs of any buildings which require artificial cooling^11,32. Furthermore, if vegetation is deciduous it allows sunlight through during the winter months when shading is not required.     

 

Green infrastructure may be important for supporting other adaptation measures. For example, since green spaces also help to reduce noise³³ and air pollution^34,36 they may help to encourage residents to cool bedrooms by leaving windows open during the night during periods of hot weather. (See also Adapting Buildings and Six Steps to Flood Resilience)

The benefits of green infrastructure are particularly helpful where neighbourhood communities are highly vulnerable due to personal, social or other environmental factors, such as building types. Interventions which cool neighbourhoods or provide cool spaces within them may be helpful in a range of cases, for example for:

• People on low incomes living in accommodation requiring adaptation who may not be able to afford the necessary adaptations to cool their homes in summer.
• People in accommodation maintained or managed by others who may have limited capacity to make changes.
• Sensitive people who may be living in accommodation which increases their exposure to high temperatures.   Older people who live in multi-occupancy flats may be particularly vulnerable because of a tendency for the flats to overheat and because it may be more difficult for occupants to easily gain access to outdoor spaces which may be cooler³⁷. In addition, restrictions on window openings in care homes or in high-rise flats can make it difficult for occupants to self-moderate temperatures during hot weather.

 

 

Flooding and green infrastructure

 

For those living in urban areas, increased surface sealing by roofs, roads, car parks, walkways and paved over gardens reduces the ability of drainage systems to remove runoff created during intense rainfall events or as a result of flooding.Where water cannot be absorbed into the ground because of built surfaces (or surfaces which are otherwise impermeable such as due to being frozen, very wet or very dry) it forms surface runoff. This runoff is quickly channelled into any drainage systems. If the rates of rainfall and subsequent runoff are higher than the capacity of the drainage system it can cause surface water flooding.  

 

There are many ways that water from any sort of flood event can enter buildings and damage its structure, services and contents³⁹. Although there are technologies available to prevent or reduce the problem, average costs of £4,700 per property⁴⁰ can be prohibitive, and unaffordable to those on low incomes⁴¹ (See also Adapting Buildings).

 

Green infrastructure has a potential to modify rates of water flow over the ground and also provide areas for water storage during high rainfall or other flood events. For example, the Victoria Business Improvement District in London includes plans for 25ha of green roofs with the potential for handling some 80, 000m³ of runoff in an area known to be susceptible to surface water flooding⁴¹. Such initiatives can be expected to have wider community benefits for people working in the vicinity. Runoff reduction has been shown experimentally in Manchester for trees and for greenroofs through partnership between the University of Manchester, Red Rose Forest and Manchester City Council^42,43. An analysis of 69 rainfall events in showed that an established green roof in Manchester city centre retained an average of two-thirds of runoff compared to only one third on a neighbouring conventional roof⁴⁴. Figure 1 quantifies the considerable reduction in runoff expected by trees and especially by grass relative to neighbouring asphalt surfaces⁴⁵. The reductions in runoff from tree and grass cover Trees in This reduction in runoff reduces the likelihood of drainage systems becoming overwhelmed. Green infrastructure is therefore often part of wider Sustainable Urban Drainage (SUDS) initiatives which may also include other design elements⁴⁶. Various evidence reviews and practitioner summaries, are available, for example:

• Academic literature reviews ⁹, ^11,47
• Evidence and policy summaries for particular urban areas^10,48
• National or generic guidance^{12,49, 50, 51}

Figure 1: Runoff proportions for different surface covers based on experimental plots in Manchester in 2011⁵²

 

Green infrastructure is particularly helpful where local communities are highly vulnerable due to personal, social or other environmental factors, such as living in buildings which may be more likely to be affected by flooding, such as basement homes. Interventions which reduce the potential for flooding in the wider community may be helpful in a range of cases, for example for:

• People on low incomes living in accommodation requiring adaptation.
• People in accommodation maintained or managed by others who may have limited capacity to make changes.

 

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