How does turning land into a city change the way water, heat and pollution move through it?
Topic 5.10 Urbanization: explain the environmental effects of urbanization, including impervious surfaces, runoff, the urban heat island, sprawl and saltwater intrusion.
A focused answer to APES Topic 5.10, covering urbanization, impervious surfaces and increased runoff, the urban heat island effect, urban sprawl, depletion and saltwater intrusion, and the benefits of smart growth, with a worked impervious-surface calculation.
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What this topic is asking
The College Board (Topic 5.10) wants you to explain the environmental effects of urbanization: more impervious surface and runoff, the urban heat island, sprawl, groundwater depletion and saltwater intrusion, and how smart growth reduces these.
Impervious surfaces and runoff
The urban heat island
Sprawl, depletion and intrusion
Reducing the impact
Smart growth concentrates development, mixes land uses and supports public transit; green roofs, permeable pavement, rain gardens and urban green space restore infiltration and cooling; public transit cuts car emissions. These reduce runoff, heat and sprawl.
Why this matters
Urbanization is where most people live, so its impacts on watersheds (Topic 4.6), water quality, climate and habitat are central. It connects to runoff reduction (Topic 5.13), the ecological footprint (Topic 5.11), and sustainability (Topic 5.12), and is a key application of land-use planning.
Try this
Q1. Identify the effect that makes cities warmer than surrounding rural areas. [1 point]
- Cue. The urban heat island effect.
Q2. Explain how converting farmland to a paved suburb increases local flooding. [2 points]
- Cue. Paving creates impervious surfaces that stop rain from infiltrating, so far more of it becomes fast surface runoff; this larger, quicker flow overwhelms drainage and raises peak flows, causing flooding.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2022 (style)4 marksSection II (FRQ). (a) Explain how impervious surfaces in a city increase stormwater runoff. (b) Describe the urban heat island effect and one of its causes. (c) Identify one environmental problem caused by urban sprawl. (d) Describe one strategy that reduces the environmental impact of urban development.Show worked answer →
A 4-point FRQ on urbanization.
(a) Explain (1 point): impervious surfaces (roads, roofs, car parks) prevent rain from infiltrating, so almost all of it becomes fast surface runoff, increasing peak flows and flooding.
(b) Describe (1 point): the urban heat island effect is the tendency for cities to be warmer than surrounding rural areas, caused by heat-absorbing dark surfaces (asphalt, concrete), waste heat, and lack of vegetation.
(c) Identify (1 point): urban sprawl consumes farmland and habitat, increases car dependence and emissions, and extends impervious cover and infrastructure.
(d) Describe (1 point): a strategy such as smart growth, green roofs, permeable pavement, public transit, urban green space, or rain gardens.
Markers reward blocked infiltration for runoff, the warmer-than-rural definition with a cause, a real sprawl impact, and a valid mitigation strategy.
AP 2019 (style)1 marksSection I (multiple choice). The urban heat island effect is best described as: (A) cities being cooler than surrounding rural areas (B) cities being warmer than surrounding rural areas (C) increased rainfall over oceans (D) cooling caused by tall buildings shading streets. Justify your choice.Show worked answer →
A 1-point MCQ on urbanization. The answer is (B).
The urban heat island effect is the tendency for urban areas to be warmer than nearby rural areas, because dark paved and roofed surfaces absorb and re-emit heat, vehicles and buildings release waste heat, and there is little cooling vegetation. (A) is the opposite; (C) is unrelated; (D) is wrong because cities are warmer, not cooler. The trap is the direction; cities are warmer, not cooler, than their surroundings.
Related dot points
- Topic 5.13 Methods to Reduce Urban Runoff: describe methods such as permeable pavement, rain gardens, green roofs and retention ponds that reduce urban stormwater runoff.
A focused answer to APES Topic 5.13, covering methods to reduce urban stormwater runoff (permeable pavement, rain gardens, green roofs, retention ponds, planting trees), how each restores infiltration and filters pollutants, and their benefits, with a worked runoff-reduction calculation.
- Topic 5.11 Ecological Footprints: define the ecological footprint, explain what it measures, and compare footprints between countries and lifestyles.
A focused answer to APES Topic 5.11, covering the ecological footprint, what it measures, the factors that raise or lower it, biocapacity and overshoot, comparison between countries, and how to interpret footprint data, with a worked footprint calculation.
- Topic 5.9 Impacts of Mining: compare surface and subsurface mining and explain their environmental consequences, including acid mine drainage and tailings.
A focused answer to APES Topic 5.9, covering surface mining (strip, open-pit, mountaintop removal) and subsurface mining, their environmental consequences, acid mine drainage, tailings, habitat destruction, and reclamation, with a worked overburden calculation.
- Topic 4.6 Watersheds: define a watershed, describe the factors that affect its characteristics, and explain how land use changes runoff and water quality.
A focused answer to APES Topic 4.6, covering the definition of a watershed, divides, the factors that shape watershed behavior (area, slope, vegetation, soil), runoff versus infiltration, and how land use affects flooding and water quality, with a worked runoff comparison.
- Topic 5.12 Introduction to Sustainability: define sustainability and sustainable yield, and explain the indicators used to assess whether resource use is sustainable.
A focused answer to APES Topic 5.12, covering sustainability, sustainable yield, the difference between renewable and non-renewable resources, indicators of sustainability (biodiversity, soil, water, productivity), and the link to natural capital, with a worked sustainable-yield calculation.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)