Hot cities

The idea

Cities are warmer than surrounding rural areas because steel, concrete, brick and asphalt absorb solar radiation, retain heat and re-radiate it, while vegetated rural areas stay cool through shade and transpiration.

City and village

After a hot summer day, a night in the middle of a city feels warmer than a night in a village nearby.

Why might that be?

• Different surfaces hold heat differently
• Cities get more sunshine from the Sun
• Villages have no sunlight

Heat in two places

Press Next step.

An island of heat

The same sun shines on both places. The difference lies in what the ground is made of and what covers it. People change the land, and that changes the local climate.

Cities are warmer than surrounding rural areas because steel, concrete, brick and asphalt absorb solar radiation, retain heat and re-radiate it, while vegetated rural areas stay cool through shade and transpiration. This is the urban heat island effect.

Notes

Cities are warmer than rural areas because steel, concrete, brick and asphalt absorb, retain and re-radiate heat, while vegetation cools through shade and transpiration.

Check yourself

How do cities compare with the rural areas around them?

Which materials in cities absorb solar radiation and retain heat?

How do rural areas and forests stay cool?

What does the urban heat island effect show?

• They are warmer, especially in summer and at night — correct. Yes!
• They are cooler because buildings give shade. The chapter says cities are warmer. Their materials absorb solar radiation and retain heat.
• They have the same temperature. Cities are warmer than the surrounding rural areas.
• Trees, grass and other plants. Vegetation helps keep rural areas cool through shade and transpiration.
• Steel, concrete, brick and asphalt — correct. Yes!
• Shade and plant leaves. Shade and transpiration are what keep rural areas cool.
• By re-radiating stored heat at night. Re-radiated heat is what warms cities. Rural areas stay cool through shade and plant transpiration.
• By having more buildings of concrete. Concrete absorbs solar radiation and retains heat, so it warms an area.
• Through shade and plant transpiration — correct. Yes!
• Human land use can alter the local climate — correct. Yes!
• The Sun shines only on cities. The Sun shines on rural areas too. The difference comes from the surfaces and what covers them.
• Rural areas have more air conditioning. The chapter says warm cities need more energy for air conditioning.