Impacts of Urbanization (College Board AP® Environmental Science): Study Guide

Resource depletion and saltwater intrusion

Resource depletion due to urbanization

• Urbanization increases demand for natural resources, such as water, energy, and raw materials

  • This leads to rapid depletion of these resources

• As cities expand, more land is cleared for housing, industry, and infrastructure

  • This reduces forests and agricultural land

• Freshwater consumption increases due to growing populations and industries

  • This puts stress on local water supplies

• Higher energy demands lead to greater reliance on fossil fuels

• Overuse of groundwater lowers the water table

  • This makes it harder for communities and agriculture to access water

  • Example: California’s Central Valley experiences water shortages due to excessive groundwater pumping for agriculture and urban use

Saltwater intrusion and its causes

• Saltwater intrusion occurs when seawater seeps into freshwater aquifers

  • This makes the water undrinkable and unsuitable for agriculture

• Excessive groundwater extraction lowers natural pressure

  • Normally, freshwater in underground aquifers is under natural pressure, which helps keep saltwater from seeping in

  • When too much groundwater is removed, the pressure weakens, reducing the ability of the aquifer to block saltwater

  • This allows saltwater to enter freshwater reserves, contaminating the supply

• Coastal urban areas are especially vulnerable

  • Many rely on groundwater wells for drinking water

• Rising sea levels from climate change contribute to increased saltwater intrusion

  • This has made the problem of saltwater intrusion even worse in coastal cities

  • Example: Miami, Florida faces saltwater intrusion as excessive groundwater use and rising sea levels threaten freshwater supplies

Impacts of urbanization on the carbon cycle

How urbanization affects the carbon cycle

• Urbanization increases carbon dioxide (CO₂) emissions, disrupting the natural carbon cycle

  • The burning of fossil fuels releases large amounts of CO₂, contributing to climate change

  • Landfills generate methane (CH₄), a potent greenhouse gas, as organic waste decomposes

Sources of carbon emissions in urban areas

Transportation

• Vehicles powered by gasoline and diesel burn fossil fuels, releasing CO₂

• Increased traffic congestion leads to higher per capita emissions

Industrial activities

• Factories and power plants rely on coal, oil, and natural gas, emitting large amounts of CO₂

• Some industries, such as cement production, release CO₂ directly through chemical reactions

Electricity generation

• Many urban areas depend on coal and natural gas power plants, leading to significant carbon emissions

• High electricity demand in cities increases the reliance on fossil fuel-based energy sources

Deforestation and land-use changes

• Expanding cities require land clearance, leading to loss of trees that absorb CO₂

• Concrete, asphalt, and buildings store little to no carbon, unlike forests or natural landscapes

Landfills and waste management

• Organic waste decomposes in anaerobic conditions, producing methane (CH₄), which is 25 times more potent than CO₂ in trapping heat

• Improper waste management further contributes to greenhouse gas emissions

Urban impervious surfaces

What are impervious surfaces?

• Impervious surfaces are human-made structures that do not allow water to penetrate the soil

  • Examples include roads, buildings, sidewalks, and parking lots

  • These surfaces prevent natural water infiltration, altering the hydrologic cycle

Impacts of impervious surfaces

Increased surface runoff

• Water that cannot infiltrate the soil accumulates on impervious surfaces, leading to excessive runoff

• Higher runoff volumes increase flood risks, especially in urban areas with poor drainage systems

Water pollution

• Runoff from impervious surfaces collects oil, heavy metals, pesticides, and other pollutants

• Contaminated runoff flows into rivers, lakes, and oceans, harming aquatic ecosystems

  • Example: Stormwater runoff in densely populated cities like New York and Los Angeles carries pollutants into waterways

Reduced groundwater recharge

• Less infiltration into the soil means groundwater supplies are not replenished

• Lower groundwater levels can cause water shortages

  • Example: Regions with high urbanization, such as Southern California, struggle with groundwater depletion

Urban heat island effect

• Impervious surfaces absorb and retain heat, raising local temperatures

• Higher temperatures increase energy demands for air conditioning, leading to more fossil fuel consumption

  • Example: Cities like Tokyo experience extreme heat due to extensive impervious surfaces

What is urban sprawl?

Definition of urban sprawl

• Urban sprawl is the expansion of low-density residential areas into previously undeveloped rural land

  • This shift moves populations from high-density urban centers to suburban and exurban areas

  • Often results in larger homes, increased car dependency, and reduced reliance on public transit

Causes of urban sprawl

Population growth

• As cities grow, housing demand increases, leading to expansion into surrounding rural areas

• Affordable housing in suburban regions attracts families away from urban centers

Transportation advancements

• Highway development makes commuting from distant areas more convenient

• Availability of cars enables people to live farther from workplaces and city centers

Land availability and lower costs

• Land in suburban and rural areas is cheaper than in urban centers

• Developers construct single-family homes and shopping centers, spreading communities outward

Desire for a suburban lifestyle

• Many people prefer larger homes, green spaces, and quieter neighborhoods

• Lower crime rates and better schools often attract families to suburban areas

Environmental impacts of urban sprawl

Habitat destruction

• Expanding suburban developments replace forests, wetlands, and farmland

• Loss of biodiversity as wildlife habitats are fragmented

Increased air pollution

• More cars on the road due to longer commutes increase CO₂ emissions

• Reduced public transit use leads to higher per capita fuel consumption

Water resource depletion

• Greater demand for water for new homes, lawns, and landscaping

• Impervious surfaces like roads and parking lots reduce groundwater recharge

Higher energy consumption

• Suburban homes require more energy for heating and cooling due to larger sizes

• Spread-out communities increase reliance on fossil fuels for transportation and daily activities