Abstract
Urban areas face a conundrum, they need to reduce their greenhouse gas emissions and consumption of resources, whilst also increasing their resilience to climate change and extreme weather, and improving wellbeing. However, it is widely recognized that well intended intervention to address one of these sustainability objectives in isolation can undermine other objectives. This paper presents a framework to efficiently identify spatial development strategies that provide the best outcomes against multiple objectives. The framework has been applied to London (UK) to identify strategies that can simultaneously: (i) minimize exposure to future heat wave events; (ii) minimize the risk from flood events; (iii) minimize transport emissions; (iv) minimize urban sprawl; (v) maximize brownfield development; and, (vi) prevent development of greenspace that is recognized as important to wellbeing. Prioritizing each objective in isolation leads to considerably different spatial planning structures, exposing conflicts between many objectives. These include tradeoffs between urban heat risk and transport emissions; and also previously undocumented conflicts between minimizing flood and heat risks. Allowing greater flexibility in development density is shown to provide benefits in terms of heat risk reduction, whilst not significantly affecting mitigation objectives. The framework is shown to significantly improve upon the London Spatial Development Strategy for the objectives analyzed. Further analysis identifies optimal spatial strategies to achieve a Low Carbon, Low Risk or Low Density city - however, these cannot be simultaneously maximized. This work shows there are difficult, and often irreconcilable, choices to be made in the spatial planning of sustainable cities. Spatial search and optimization tools strengthen the evidence-base for planning. Rapid identification of development strategies that satisfy, and minimize conflicts between, multiple objectives helps planners to develop strategies that simultaneously improve urban sustainability and reduce the risks from natural hazards.
Highlights
There is sufficient data available in London to analyse a number of climate risk and sustainability objectives, and strong engagement with key stakeholders in the Greater London Authority (GLA) and other organisations who have articulated a wide range of planning choices
Planners in London have to address a tradeoff between increases in heat risk, or higher transport emissions and urban sprawl
If reducing transport emissions leads exposes more people to heat risk this can be fed into the planning process, and permission to develop only granted if the development is designed to mitigate urban heat island effects, for example through use of green spaces, rooftop gardens and uses of surfaces with a higher albedo that reflect more heat
Summary
Most urban growth is expected to be concentrated in locations susceptible to natural hazards (McGranahan, Balk, & Anderson, 2007). This coupled with the often poor design of cities (Mitchell, 1999) will significantly increase the environmental risks faced by cities in the future (Hunt & Watkiss, 2011), especially from more frequent and severe extreme weather events due to projected climate change (IPCC, 2013). London, governed by the Greater London Authority (GLA), is a focal point for sustainable development initiatives in the UK and internationally (Walsh et al, 2013) and with population projected to increase by approximately a million people between 2011 and 2031 (GLA, 2011a), London will require substantial new development. The Mayor of London has set an ambitious target to reduce greenhouse gas emissions by 60% from 1990 levels by 2025 (GLA et al, 2011)
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