A sustainable city is a city which has been designed with environmental concerns in mind. A large percentage of the human population around the world lives in cities and urban areas, underscoring the need for sustainable practices in these environments. Sustainable cities aim to change the way they operate for the benefit of future generations, ensuring that they do not put a strain on resources which will cause such resources to vanish before future generations have an opportunity to benefit from them.
Sustainability is a complex topic. On a basic level, it involves practices which are designed to be sustainable in the long term, meaning that people can continue using these practices without harming the environment, and possibly with some benefit to the environment. On a city-wide level, sustainability encompasses a wide variety of changes, all of which are intended to reduce the environmental impact of the city as a whole. These changes can include individual lifestyle changes made by citizens as well as city-wide shifts in policy.
One goal of a sustainable city is to reduce needs and reliance on surrounding areas. In addition to being environmentally sustainable, this can also be economically beneficial, and may allow a city to be more secure in the event of a natural or civil emergency. Reduction of reliance on surrounding areas includes growing food in a city, reducing water needs and reusing water as much as possible, and generating energy inside the city. The city may become independent of the surrounding area, reducing strain on outlying communities.
A sustainable city must also think about what it is putting out into the surrounding environment. Sustainable cities want to reduce waste in addition to lowering pollution. This is especially important in cities with limited processing capacity for things like waste, as such materials may be pushed onto surrounding communities unless the city takes responsibility for them.
Some examples of things a sustainable city might implement include: green roofs, rooftop gardens, solar panels, bike lanes, better public transit, water recycling, centralized recycling facilities, energy efficient heating and cooling systems for large buildings, reuse of building materials, changes to the workweek which reduce congestion, tougher air quality controls, permeable pavement, wind energy, and community service programs. These changes may not have immediate effects and they can take years or decades to implement, but over time, they can have a cumulative benefit. Just installing green roofs in a sustainable city, for example, can radically reduce the rise in temperature commonly associated with cities.