Mitigating the negative effects of the urban heat island in the UK on an urban block scale. An approach towards sustainable neighbourhood design
The thermally massive and impermeable concrete cities that have evolved over time have produced separate urban microclimates. The trapping of solar energy in the urban fabric and waste anthropogenic heat causes an urban heat island (UHI), which in London can cause the centre to be up to 6-8°C hotter than the surrounding countryside (GLA, 2006). The urban heat island causes an increase in building cooling loads, water use, air pollution, sickness and discomfort, and it is expected it to increase with climate change.
Regional strategies are currently being developed for London and Manchester to combat today’s UHIs, but there is little guidance on how future UHIs could be mitigated through intelligent design of new developments. Such neighbourhoods will be around for the next 40 or 50 years, when the UK is expected to experience significantly hotter drier summers, and so may need to be retrofitted with mitigation measures in the future.
This research examines a number of the available mitigation techniques. They are studied for their wider engineering, environmental, social and economic impact. Thermal imagery is used to assess their effect on surface temperatures. They are also analysed against a case study site, the planned Cambridge Railway Station neighbourhood scale development, known as cb1. A list of wider impacts to consider and the techniques they are affected by are presented.
The result of this research is a set of guiding questions that can be used to help develop an urban strategy to mitigate UHI. It is determined that although the cb1 development is unlikely to significantly increase the atmospheric UHI, this site is at risk in the future of being in the centre of a larger UHI. The process by which a designer should then build mitigation of the UHI into a new neighbourhood development design is presented. It is found that to produce a sustainable urban environment a range of mitigation technologies are needed and that their effectiveness and wider impacts will depend on how they are used within the site