Urban Heat Islands

An urban heat island is a metropolitan area which is

significantly warmer than its surrounding rural areas.

Bare earth and vegetation

Water

Albedo

Buildings and the Ground Store Heat

Sources of Heat

Cityscapes v landscapes

Energy in and out

London, 2000

British Museum

Richmond Park

London, Summer 2000

Sunrise sunset

Chicago

The urban heat island is biggest…

• At night (before sunrise)

• In the summer

• When there is no wind

• When the sky is clear

• When the weather doesn’t change through the night

Excess mortality rates in early August 2003 indicate about 40,000 heat-related deaths

Daily mortality in Baden-Württemberg

observationsHadCM3 Medium-High

2003

2050s

Tem

per

atu

re a

no

mal

y (w

rt 1

961-

90)

°C

European 2003 summer temperatures

“Right now, we average about 14 days each summer above 90

degrees in New York. In a couple of decades, we could be experiencing 30

days or more,”

What’s that got to do with the UHI?

• London – 600 heat related deaths in August 2003

• Up to 9 °C warmer than surrounding rural areas• Mortality increases with temperature when

temperatures are over 22°C• Mortality particularly linked to warm night time

temperatures• Mortality linked to age, sex, deprivation etc.• Challenge now to design buildings and urban

areas for the future – which will see more people living in cities, and will be warmer.

Other Consequences

• The growing season can be up to 15 days longer in a city!

• Warmer in a city in winter

• Rainfall

How to reduce urban heat islands