Explain how increasing urbanisation can lead to flooding in an area that was previously forested.

Cambridge International IGCSE Biology (0610) — 20.2 Habitat destruction · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Urbanisation removes trees, so less rainfall is intercepted by foliage.
2. Tree roots are lost, reducing the soil’s ability to absorb water.
3. Without trees, water runs off the surface more quickly, increasing the rate of flow.
4. The rapid surface runoff causes water to accumulate faster, leading to flooding.

Examiner tips

Use the exact phrases from the mark scheme (e.g., ‘interception of rainfall’, ‘tree roots to anchor the soil’).
Show the causal chain: removal of trees → less interception → less absorption → faster runoff → flooding.

Common mistakes

Confusing ‘interception’ with ‘runoff’ or omitting the role of tree roots.

Mark scheme (4 marks)

Trees are removed during urbanisation, reducing the interception of rainfall
Without tree roots to anchor the soil, water cannot be absorbed into the ground as effectively
Forests slow the rate at which water reaches the ground; without them, water reaches the ground faster
Water accumulates more rapidly on the surface, causing flooding

Key terms in this question

urbanisation · flooding