© Crown copyright Met Office Climate Change, Cities, and the Urban Heat Island Mark McCarthy, Martin Best, Richard Betts, Maggie Hendry

© Crown copyright Met Office Contents This presentation covers the following areas Human exposure to climate stress. A simple coupled urban-climate model. Energy use and the urban environment. Cities in a regional climate model.

© Crown copyright Met Office Impact of climate change on human settlements is driven by population dynamics and climate.

© Crown copyright Met Office Majority of population residing within urban areas Figure from the UN department of Economic and Social Affairs

© Crown copyright Met Office Human Exposure to climate stress Population dynamics and urbanisation will contribute to future exposure of humans to climate stress. Can we design climate models that are useful impacts and adaptation tools despite uncertainties?

© Crown copyright Met Office A simple urban climate model Mark McCarthy

© Crown copyright Met Office A simple urban scheme for a climate model Ground Atmosphere C(dT/dt)+G=R n -H-LE-Q f HLELWSW Best et al. 2006: Boundary layer Meteorology 118:

© Crown copyright Met Office Subgrid heterogeneity Urban parameters: Albedo Roughness length of heat and momentum Heat Capacity Anthropogenic heat release Impervious surface Essery et al. 2003: J. Hydrometeorology, 4, pp

© Crown copyright Met Office Urban Heat Island responds to climate feedbacks but not forcings in a 2XCO2 experiment Diurnal Temperature Range

© Crown copyright Met Office Energy use Mark McCarthy

© Crown copyright Met Office Energy use and urban heat islands. Energy use data courtesy of London Energy and CO2 inventory 2003

© Crown copyright Met Office Change in average temp. Change in 95 th %ile temp. Global mean change 2*CO2 2*CO2 + UHI 2*CO2 + UHI + 60Wm -2 2*CO2 + UHI + 20Wm -2

© Crown copyright Met Office Energy use and climate. Load data courtesy of EDF energy

© Crown copyright Met Office Energy use-climate-urban feedbacks Urban climates can change in response to climate change. Urban climates can change in response to local anthropogenic forcing. Local anthropogenic forcing can change in response to climate.

© Crown copyright Met Office Cities in a regional climate model Mark McCarthy

© Crown copyright Met Office Urban heat islands in HadRM3 – offline ‘v’ coupled Obs Model London Weather Centre St James Park Heathrow Northolt 2oC2oC

© Crown copyright Met Office Seasonality and magnitude of a heat island simulated by RCM LWC – Wisley Observations SJP – Wisley Observations HadRM3 London

© Crown copyright Met Office Anthropogenic heating and extremes. Avg annual no. of hot nights (>20 o C): Present day Climate: No urban = 0.45 Coupled urban = 2.9 Coupled urban + 25Wm -2 = 4.2 Coupled urban + 75Wm -2 = 4.4 With 2.5 o C Climate Change: No urban = 3.5 Coupled urban = 14.6 Coupled urban + 25Wm -2 = 16 Coupled urban + 75Wm -2 = 22

© Crown copyright Met Office Summary. Forcings and feedbacks between climate, local heat release, and the urban heat island require coupled climate-urban models. Met Office UM provides one such framework. Simple scheme captures UHI. Warming similar for vegetation and urban surface in HadCM3 Local heating is significant additional driver of change Feedbacks are important in 25km regional model Important for capturing extremes in night time temperatures.

© Crown copyright Met Office Objectives. Improved quantification of urbanisation and anthropogenic heating in climate change. Urban model development, assessment and uncertainty (Maggie Hendry – 9am Weds) Collaborations to develop urban planning tools and impact assessments: SCORCHIO (SCORCHIO - Sustainable Cities: Options for Responding to Climate cHange Impacts and Outcomes. CIRCE – Climate Change and Impacts research: The Mediterranean environment