⏳ Estimated Reading Time: 8 - 10 minutes

Describe the effects of urbanization on the environment.

Urbanization

A cityscape at night. — **City living is convenient and can be beautiful, but there are environmental consequences of having so many people living close together.**

Early communities were hubs of trade. Many people lived outside of the community and only traveled into it to pick up supplies or trade excess goods. These hubs eventually became the towns and cities with which we are familiar today.

Growing communities resulted in more jobs and opportunities and this resulted in a general movement from country living to city living. Cities began to grow larger and urban living became the dominant way of life. This movement into cities by human populations is known as urbanization.

As the human population increased, more people elected to live in densely populated cities to take advantage of the jobs and resources available. Cities became more densely populated with humans and problems such as waste disposal, air quality, and water quality began to be commonplace.

Urban Sprawl

a well-organized suburban neighborhood. The houses are closely packed, showcasing a variety of designs and colors, surrounded by neatly trimmed lawns and trees. — **Urban sprawl is when people move out of the city and into suburban areas.**

Urbanization can lead to urban sprawl, a condition in which cities grow outward, enveloping more and more natural environments. Urban sprawl is a far-flung urban-suburban network of low-density housing areas, shopping malls, industrial parks, and other facilities tied loosely together by multilane highways. Sprawl is measured using 4 different factors:

Residential density: the lower the density, the more sprawl
Neighborhood mix: the less mixed, the more sprawl
Accessibility of street networks: poor connections and few routes mean more sprawl
Strength of activity centers and downtowns: the less well-defined a downtown, the more sprawl

Many people now live in the suburbs and commute (use transportation) to the city for work. Sprawl, however, provides little to no advantage in commute times. People are still traveling between 30 to 60 minutes to work.

traffic clogging a roadway — **Sprawl increases energy demands, especially fuel for vehicles.**

Areas with large amounts of urban sprawl also have larger energy demands, especially petroleum. The people living and working in these areas need to be able to drive to work, shopping, and their homes and all of this requires gasoline.

Essential Knowledge

Urban sprawl is the change in population distribution from high population density areas that spread into rural lands, leading to potential environmental problems.

Urban Blight

an image of a dilapidated and abandoned industrial building. — **Exurban migration can initiate a positive feedback loop known as urban blight.**

Even more recently, a trend has begun where people move to the exurbs, which are areas similar to suburbs, but even farther away from the city center. When considering where to live, people tend to make choices based on personal good rather than the common good, and it's hard to blame them.

This exurban migration, or relocation of people from inside the city to outside the city, means that city populations have been declining over the last 50 years, causing a vicious cycle of problems in urban areas. Urban sprawl accentuates the concentration of poor people in high-density, inner-city, or aging suburban communities because these people cannot afford to move away from these areas.

Local governments are responsible for public schools, local roads, police and fire protection, waste collection and disposal, water and sewers, and recreational services. Property taxes are the major source of revenue to pay for these services. When the richer people move away from the cities, the only ones left to pay property taxes are the poorer residents. This reduces the revenue available to the city, which in turn reduces the funding for those services that the city is responsible for providing. This causes a positive feedback loop with more and more people moving away from the cities, reducing revenue, reducing the quality of public services like schools, and further causing people to move away from the cities. This positive feedback loop is known as urban blight or urban decay.

A revitalized city, looking clean and new — **Many cities are experiencing revitalization, which is a trend in which people and businesses move BACK to the city.**

Revitalization

Some urban areas, however, have experienced a revitalization, or trend in people and businesses moving back to the city.

Revitalization can break the positive feedback loop associated with exurban migration leading to better living conditions in urban areas. As living conditions improve, more people and businesses seek to move into the urban area which then increases the tax base. Increased tax revenue leads to more improvements in infrastructure which further improves living conditions. Revitalization is a slow process for the most part, but it is ongoing in many large urban areas of the United States.

Impacts of Urban Areas

Urbanization has wide-ranging impacts on the environment and humans. For example, my brother lives in Washington D.C. and is asthmatic. He started wearing a mask before COVID and continues to wear the mask. If he doesn't wear it, he will get sick. But he loves the convenience of living in the city, so he wears the mask.

Explore the tabs below to learn more about each impact on urban areas. Have you noticed any of these issues in your city or if you've visited a large city?

Water Cycle
Atmosphere
Natural Areas
Human Health

Impacts on the Water Cycle

A large, round tunnel opening is visible at the base of a concrete wall. The ground in front of the tunnel is covered with water, suggesting that this might be a drainage system or outlet for excess water.

Large concentrations of humans in one place have significant impacts on water resources in the area. Many cities developed near rivers, lakes, or coastlines to take advantage of water for drinking, transportation, and waste disposal. Because of waste disposal, waterways began to become severely polluted, first with human waste and, later, with chemicals and fertilizers from industries and homes.

Water needs to get to the residents but can also become polluted easily. Aquatic species declined and sanitation became problematic due to the presence of human waste in drinking water. A concerted effort to deal with sewage (human waste) led to the establishment of sewage treatment plants which largely solved the problem of human waste pollution. Laws such as the Clean Water Act 💧 made it illegal for companies to dump their waste directly into waterways and, over time and with help from humans, aquatic ecosystems and species made a remarkable comeback.

A muddy terrain with water partially covering the surface. In the foreground, there is a round, metallic object, resembling a manhole cover, partially submerged in the mud. — **Impervious surfaces increase the amount of runoff and decrease the amount of infiltration.**

Today’s water pollution problems around urban areas relate mostly to stormwater runoff, which is water that runs off into waterways during rainstorms. Impervious surfaces such as concrete and pavement don’t allow rainfall to percolate down into the soil. Pollutants on these paved surfaces are also carried by runoff to surface waters, degrading water quality. It has to go somewhere so it runs off into the nearest drains, streams, and rivers. Stormwater runoff adds tons of pollution into waterways in the form of oil leaked from vehicle engines, fertilizers from lawn applications, animal waste, salt from roadways salted in winter, and discarded plastic litter, just to name a few contaminants.

Runoff is such an important issue in urban areas, that we will discuss it further in the next lesson.

Impacts on the Atmosphere

A cityscape captured under a hazy sky, giving an impression of air pollution or fog. — **When millions of people live in an urban setting, air pollution becomes a significant issue.**

When millions of people live in an urban setting, air pollution also becomes a significant issue.

Air pollution in early cities resulted from burning materials for heating homes and buildings along with heat needed for industrial processes and cooking. Wood, and then coal, was the primary choice of fuel. With the invention of the internal combustion engine combined with the discovery of oil, fossil fuels derived from petroleum began to dominate.

Transportation, though, is the biggest culprit when it comes to air pollution in urban areas. From 1950 to 2007, oil consumption tripled, even though the population only doubled. This translates to a 63% increase per capita in gasoline consumption.

Additionally, transportation accounts for 28% of greenhouse gas emissions, so it is a significant contributor to global climate change and the increasing warming of our planet.

Burning fossil fuels also disrupts the carbon cycle as more and more carbon dioxide and carbon monoxide is added to the atmosphere, accelerating global climate change.

Industrial processes, construction, and other businesses emit other types of air pollutants - particulate matter, nitrogen oxides, and sulfur oxides to urban air.

a traffic scene where multiple cars are emitting exhaust fumes and chemical formulas "CO2", "SO2", and "NO2" are labeled near the respective smoke plumes, indicating the types of gases being emitted. — **Vehicles produce 80% of the air pollution in metropolitan areas.**

Some of these air pollutants chemically mix together in the atmosphere form substances such as ozone which damages certain human-made materials as well as impacting human health, which we will discuss on the last tab.

Impacts on Natural Areas

An aerial view of a landscape divided into different sections by roads. — **A loss of agricultural land is probably the most serious problem with urban sprawl in the long run.**

Sprawl also causes a loss of agricultural land. This is probably the most serious problem with urban sprawl in the long run.

Our population is growing exponentially, yet cropland is declining at a rate of 1.3 million acres/year. On average, food now travels 1000 miles from farm to table. Between 1982 and 1992, we developed about 1.4 million acres/year. From 1997 to 2003, we developed 1.75 million acres/year, so we are increasing our development, causing the fragmentation of wildlife areas, habitat destruction, and a loss of biodiversity.

Impacts on Human Health

An image of a person wearing a mask, standing outdoors with a cityscape in the background. — **Urban air pollution can have a negative effect on the respiratory system of residents.**

Sprawl also has human health effects.

More people own vehicles and are driving farther and farther distances to work. With more time spent in a car, less time is spent outside and on physical activity, causing all the health effects that a sedentary lifestyle produces – obesity, diabetes, heart disease, etc.

Additionally, becoming stuck in traffic jams exposes the occupants of vehicles to air pollutants such as carbon monoxide, a colorless, odorless gas from car exhaust that can lead to headaches and other health issues.

Essential Knowledge

Urbanization can lead to depletion of resources and saltwater intrusion in the hydrologic cycle.

Impervious surfaces are human-made structures - such as roads, buildings, sidewalks, and parking lots - that do not allow water to reach the soil, leading to flooding.

Urbanization, through the burning of fossil fuels and landfills, affects the carbon cycle by increasing the amount of carbon dioxide in the atmosphere.

AP Exam Tip

Urbanization has wide-ranging effects on the environment. You should know how sprawl affects the area surrounding cities.

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