Wise viewers, welcome to Planet Earth: Our Loving Home for the first in our two-part series on green roofs or rooftops covered with vegetation to reduce the Urban Heat Island effect, promote energy savings, improve air quality, grow fresh produce, minimize storm water runoff and lessen climate change.

There are two main types of green roofs - intensive and extensive. The former requires a large flat surface area, features many kinds of plants including trees and shrubs, has greater than １０ centimeters of soil substrate and is high-maintenance. The latter has less than １０ centimeters of soil substrate, is generally made up of herbs, grasses, mosses and other types of groundcover and is low-maintenance.

Today we will focus on the greening of building rooftops in metropolitan areas. In large cities, skyscrapers, concrete buildings, infrastructure and pavement trap heat from the Sun, as well as waste heat from cars, air conditioning units, factories and other sources, creating “Urban Heat Islands” or UHIs.

This effect can raise the temperature in a city two to １０ degrees Celsius higher than if it was a vegetation-filled rural area. The United Nations Intergovernmental Panel on Climate Change states in its Third Assessment Report, “It is well-known that compared to non-urban areas urban heat islands raise [both] night-time temperatures [and] daytime temperatures.”