High temperatures and heatwaves can cause large societal impacts by increasing health risks, mortality rates, and personal discomfort. These impacts are exacerbated in cities because of the Urban Heat Island (UHI) effect, and the high and increasing concentrations of people, assets and economic activities. Risks from high temperatures are now widely recognised but motivation and implementation of proportionate policy responses is inhibited by inadequate quantification of the benefits of adaptation options, and associated uncertainties. This study utilises high spatial resolution probabilistic projections of urban temperatures along with projections of demographic change, to provide a probabilistic risk assessment of heat impacts on urban society. The study focuses on Greater London and the surrounding region, assessing mortality risk, thermal discomfort in residential buildings, and adaptation options within an integrated framework. Climate change is projected to increase future heat-related mortality and residential discomfort. However, adjusting the temperature response function by 1–2 °C, to simulate adaptation and acclimatisation, reduced annual heat related mortality by 32–69 % across the scenarios tested, relative to a no adaptation scenario. Similar benefits of adaptation were seen for residential discomfort. The study also highlights additional benefits in terms of reduced mortality and residential discomfort that mitigating the urban heat island, by reducing albedo and anthropogenic heat emissions, could have.

Chris Kilsby (School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, UK ), Mark McCarthy (Met Office, Hadley Centre, Fitzroy Road, Exeter, UK ), Clare Goodess (Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norfolk, UK ), Duncan Smith ( LSE Cities, London School of Economics and Political Science, London, UK ), Nick Malleson (School of Geography, University of Leeds, Leeds, UK ), Mark Birkin (School of Geography, University of Leeds, Leeds, UK )