At present, cities allover the world are experiencing rapid
growth because of the rapid increase in the world population
and the irreversible flow of people from rural to
urban areas [1]. In the coming decades, the world’s rapid
urbanization will be one of the greatest challenges to ensure
human welfare and global environment. According to recent
estimates, cities occupy about four percent of the world’s
terrestrial surface, yet they are home to almost half of the
global population, consume close to three-quarters of the
overall natural resources, and generate three-quarters of its
pollution and wastes. The UN estimates that virtually all net
global population and economic growth over the next 30
years will occur in cities, leading to a doubling of current
population [2].