Climate Change

Climate change is recognised as a serious and cross cutting issue and the UK is the first country in the world to have introduced legally binding climate change legislation under the 2008 Climate Change Act.

According to Safeguarding our Soils, a Strategy for England (Defra 2009) soil plays a vital role in the fight against climate change. Open spaces and previously developed  land (PDL) can and will make a valuable contribution to helping both to reduce concentrations of greenhouse gases in the atmosphere (the cause of climate change), and to help adapt effectively to the impacts of change (building resilience to a changing climate).

Urban greening is a cost effective way of moderating harsh climates at a local level. Trees and vegetation have a natural cooling effect as they provide shade, potentially reducing surface temperature, by 5°C, to 20°C. In addition, evapotranspiration from vegetation consumes a significant proportion of the available heat energy in the atmosphere. This energy is used to convert water in the leaves into water vapour, which is then transpired through the trees. For some locations, it has been estimated that evapotranspiration can reduce peak summer temperatures by 5°C.

Green infrastructure provides areas where natural processes, such as evapotranspiration and runoff interception, can continue to occur. However, ecosystem services provided by green infrastructure are often overlooked and undervalued. Instead, harmful processes such as tree felling to reduce hazards near roads, development of infill in gardens and the redevelopment of biodiverse “urban wastelands” degrade the ability of the city to regulate temperature and provide other valuable services to inhabitants.

The functionality of open green spaces becomes increasingly important when viewed against the backdrop of a changing climate. The UKCIP09 climate change scenarios suggest increases in the average summer temperature of between 1°C and 5°C by the 2080s and an increase of 30% in average winter rainfall. These scenarios do not take the urban surface into account and the factor of increase is likely to be significantly higher in densely urbanised areas.

A different climate will have implications for the costs of, and approaches to, maintaining spaces such as increased watering during droughts, greater pressure on spaces as they are used more intensively and an effect on the health of some species of vegetation. Urban green spaces require an effective program of maintenance and limitations on water use, which can often stem from extended dry periods, and can affect the health of vegetated surfaces. As greenery dies its temperature moderating effects approach those of dry bare soil. Although sub-optimal, dead vegetation’s climate moderating effects remain an improvement on traditional roofing mediums.

Even as climate change tests the strategies of designers and planners, it provides them with opportunities. For example, it provides an opportunity to remodel or create outdoor spaces. The need to manage high temperatures and reduce the effects of floods and droughts justifies the creation and maintenance of green infrastructure. This leads to further positive spin-offs, as urban green spaces play a significant role in improving air quality and preserving biodiversity.

Courtyards, especially when coupled with vegetation and water features, help to moderate the microclimates of surrounding environments. Central courtyards or semi-open shaded spaces provide “cool pools” for cross ventilation of nearby spaces. The temperature of air drawn into courtyards is cooled by each courtyards mass, vegetation and a lack of insolation. This natural ventilation reduces the need for mechanical cooling and thereby the carbon footprint of a building.

Reducing the need for mechanical cooling in buildings has been a focus for UK planning guidance for some time and there is a growing interest in using design techniques to alter the temperature balance of cities. The rising recognition of the importance of green infrastructure has implications for policies that encourage infill development, higher housing densities and the reduction or loss of gardens.

In fact, policies should be used to encourage the optimal composition of urban green space through green space strategies. It may even be feasible to consider influencing the public through education, social pressure and incentives to improve the likelihood that people will change their behaviour to improve conditions. However, there are limiting factors that cannot be altered, such as soil type, and designers need to find innovative ways of incorporating adaptations into new buildings.

Figures produced by PriceWaterhouseCoopers show how a shift in spending from grey to green of just 0.5% could increase investment in urban green space by 141%. Using these figures, CABE has urged government to set up a national green infrastructure taskforce and for local government to be equipped with the skills necessary to design and manage green infrastructure. CABE argues that a shift is needed in public spending from grey projects, like road building and heavy engineering projects, to green schemes like street trees, parks, green roofs and waterways. For example, flood protection requires super-sized storm water pipes. But a combination of living roofs, large trees and soft landscaping can absorb heavy rainfall, store and recycle it for summer irrigation.

Climate change is a complex area. Clear guidance is needed for local authorities and other practitioners on how to manage public urban green spaces to respond to a warmer future. There is a need to adopt innovative design and engineering approaches to reduce urban temperatures and adapt to the future climate.

Green infrastructure supplies a route to climate change adaptation that can be applied across a range of urban settings, helping to reduce urban temperatures and carbon emissions. However, it is important to ensure that local conditions are properly considered and planned for. A high level of flexibility needs to be maintained as the future remains uncertain. Future proofing adaptation techniques need to take account of emerging technologies, the embedded carbon of solutions and the constraints imposed by future requirements. As such, green infrastructure represents the state of the art and the high level of adaptability required to cool our cities for decades to come.