6.11 Challenges of Urban Sustainability

• Sprawl: low-density growth spreads cities over farmland and natural land, increases driving and makes services more expensive to provide.
• Sanitation: in many fast-growing cities, sewer and waste systems can't keep up, so untreated waste reaches rivers and spreads disease.
• Air and water quality: traffic, industry and burning fuels pollute the air, as in Delhi, India, where winter smog is a major health threat. Runoff from streets and parking lots pollutes rivers.
• Water supply: Cape Town, South Africa, came close to running dry in 2018 during a severe drought, and Mexico City has pumped so much groundwater that parts of the city are sinking.
• Energy use: cities use most of the world's energy for buildings, transportation and industry.
• Climate change: coastal cities face sea-level rise and flooding, and pavement and buildings trap heat, creating urban heat islands several degrees warmer than the countryside. Jakarta faces both flooding and sinking land, one reason Indonesia began building a new capital, Nusantara, on Borneo.

A city's ecological footprint is the area of productive land and water needed to supply its resources (food, water, energy, materials) and absorb its waste, including carbon emissions. A large city's footprint is many times larger than the city itself, because it draws food, water and energy from far away. Wealthy, high-consuming cities tend to have larger footprints per person than poorer ones.

• Regional planning: coordinating transportation, housing and land use across many local governments in a metro area, instead of each town acting alone.
• Urban growth boundaries (UGBs): legal lines that separate land where urban development is allowed from farmland and forest outside it. Oregon's 1973 land-use law required them, and the Portland area's boundary dates from 1979.
• Brownfield remediation and redevelopment: cleaning up old industrial sites contaminated by pollution, then reusing them. The U.S. EPA estimates there are more than 450,000 brownfields nationwide. Atlanta's Atlantic Station was built on the site of a former steel mill.
• Farmland protection: buying development rights from farmers or zoning land for agriculture only, as in Lancaster County, Pennsylvania.
• Green infrastructure: parks, street trees, green roofs and wetlands that absorb stormwater and cool the city.

Each response has trade-offs. Portland's growth boundary has protected farmland and encouraged denser neighborhoods, but critics argue it limited land for housing and contributed to rising prices. Brownfield cleanups reuse land and remove pollution, but they're expensive, and new development can raise nearby rents and displace residents. Farmland protection keeps local agriculture alive but can push development farther out. Strong answers name a response, explain how it works, and weigh at least one cost.