Washington — Cities worldwide are busy planting trees to keep summer temperatures down, and for good reason.
A city with 1 million people is typically between 1 and 3 degrees Celsius warmer than the surrounding country because of the density of concrete and buildings. During the evening, the temperature discrepancy can be as high as 12 degrees Celsius.
Trees can give much-needed relief to such urban “heat islands.” In the United States, deciduous trees planted along the south side of buildings can reduce air conditioning costs by 20 percent, the U.S. Environmental Protection Agency has advised.
In Texas, home to several large cities, a program called Trees for Texas has planted 139,000 trees to cut pollution and save energy. The city of Sacramento in California has given out more than 350,000 free trees over the past decade for the same reason, and Honolulu in Hawaii now requires many parking lots to be shaded by a canopy of trees.
Similar initiatives are under way in many countries.
The Vietnamese city of Hanoi has adopted a long-term strategy to set aside 70 percent of the city for trees and water spaces. Nagoya in Japan adopted a policy in 2001 requiring tree planting for all new development plots that exceed 300 square meters. In Germany’s Stuttgart, there’s a local ordinance prohibiting the cutting of trees that have reached a certain size.
As anyone who has lived on the open plains can attest, trees can also help on a cold winter day. Howling winds can be stopped in their tracks by trees, helping households save on heating costs as well.
