6.2 Urban Heat Islands

The NASA website provides an excellent summary of urban heat islands. How do you think the land use planning in urban heat islands could be used to reduce the scale of such islands?

Heat is trapped in urban areas for a number of reasons. These mostly boil down to:

1. Lack of convection, which would distribute the heat. This is caused by tightly packed, high-rise buildings that trap air at street level.
2. Lack of evaporation. The impermeable surfaces that cover our cities and the efficient water drainage systems reduce the effect of heat loss through evaporation.
3. Heat absorption. The buildings, roads and pavements absorb heat during the day, releasing it at night, keeping the temperature high.
4. High pollution levels/ released heat from air conditioning systems.

So, to reduce this, planners might want to think about:

1. Lower-rise, more distributed buildings (obviously this has big spatial and financial implications in itself, as it would take up a lot more area, so not really practical).
2. More lakes, parks and trees. These all help with the evaporation of water and parks are proven to be cooler than the surrounding built-up areas. Also using, for example, permeable paving, which has many benefits, but costs vary a lot.

These pictures of Baltimore show the surface temperature (top) where the darker the colour, the cooler it is, and the level of development (bottom) where red is highly developed and white is low development/green space. note where the parks in the city are... The full details can be found on the Earth observatory site HERE.

3. Paint roofs white, or use reflective roofing, which would reduce the radiation hitting the building. Or green roofs, which are fantastic for so many reasons. (Exeter Uni has these at Tremough). Rooftop gardens would also help and create a lovely space for residents…
4. We can all try to reduce emissions in cities. Plus, the use of some of the above mitigation methods would start the cooling, and then we wouldn't have to use the a/c so much, therefore pumping less warm air into the neighbourhood, reducing the problem further!

Sorted!