OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

Why are areas of desertification more prone to flooding?

1. Increased forest cover slows down rainfall

2. Soil loss and river siltation lead to increased flooding risks

3. Lack of vegetation helps absorb rainfall

4. Frequent droughts cause drought-resistant plants to die

The correct answer is: Soil loss and river siltation lead to increased flooding risks

Areas of desertification often experience soil loss due to erosion and degradation of the land, which can create a situation where the soil's ability to retain water is significantly diminished. This soil degradation leads to reduced infiltration rates, meaning that when it does rain, the water cannot easily seep into the ground. Instead, the water runs off the surface, which can lead to increased flooding. Additionally, river siltation, which can occur due to the increased runoff erosion in desertified areas, can make river channels shallower and narrower over time. As this happens, there is less capacity to hold the water during heavy rainfall, further contributing to flooding risks. The combination of these factors—soil loss and reduced capacity of rivers to manage water—makes areas of desertification more susceptible to flooding when significant rainfall occurs.