Climate Change Cities and the Urban Heat Island

Climate Change, Cities, and the Urban Heat Island Mark Mc. Carthy, 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

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

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 Mc. Carthy © Crown copyright Met Office

A simple urban scheme for a climate model Atmosphere SW H LE LW C(d. T/dt)+G=Rn-H-LE-Qf Ground Best et al. 2006: Boundary layer Meteorology 118: 503 -525 © 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. 530 -543 © Crown copyright Met Office

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

Energy use • Mark Mc. Carthy © Crown copyright Met Office

Energy use and urban heat islands. © Crown copyright Met Office Energy use data courtesy of London Energy and CO 2 inventory 2003

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

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

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 Mc. Carthy © Crown copyright Met Office

Urban heat islands in Had. RM 3 – offline ‘v’ coupled Model Obs © Crown copyright Met Office London Weather Centre St James Park Heathrow Northolt 2 o. C

Seasonality and magnitude of a heat island simulated by RCM LWC – Wisley Observations SJP – Wisley Observations © Crown copyright Met Office Had. RM 3 London

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 + 25 Wm-2 = 4. 2 • Coupled urban + 75 Wm-2 = 4. 4 • With 2. 5 o. C Climate Change: • No urban = 3. 5 • Coupled urban = 14. 6 • Coupled urban + 25 Wm-2 = 16 • Coupled urban + 75 Wm-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 Had. CM 3 • Local heating is significant additional driver of change • Feedbacks are important in 25 km 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 – 9 am Weds) • Collaborations to develop urban planning tools and impact assessments: • SCORCHIO (SCORCHIO - Sustainable Cities: Options for Responding to Climate c. Hange Impacts and Outcomes. http: //www. sed. manchester. ac. uk/research/cure/research/scorchio/ • CIRCE – Climate Change and Impacts research: The Mediterranean environment http: //www. circeproject. eu/ © Crown copyright Met Office