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examBoard: Cambridge
examType: IGCSE
lessonTitle: Human Activities and Flood Risk
While flooding is a natural process, human activities have significantly altered flood patterns and increased flood risk in many parts of the world. Understanding how our actions contribute to flooding is essential for developing effective flood management strategies.
Key Definitions:
Urban development dramatically changes how water moves through an area and is one of the most significant human contributors to increased flood risk.
When we replace natural vegetation and soil with buildings, roads and car parks, we create impermeable surfaces that prevent rainwater from infiltrating into the ground. This increases the volume and speed of surface runoff, overwhelming drainage systems and causing flash floods.
Urban areas rely on drainage systems that can become overwhelmed during heavy rainfall. Older cities often have combined sewage and stormwater systems that can back up during floods, causing contamination. Even modern separate systems have capacity limits that can be exceeded.
Urbanisation creates a cycle that increases flood risk:
Studies show that converting just 10-20% of a catchment area to impermeable surfaces can double the amount of runoff compared to a natural catchment.
Forests play a crucial role in regulating water flow and preventing floods. When we remove forests, we disrupt this natural flood protection system.
Tree canopies catch rainfall, slowing its journey to the ground and allowing some to evaporate directly back to the atmosphere.
Tree roots create channels in the soil that increase water absorption and reduce surface runoff.
Without tree cover, soil erodes more easily, reducing its water-holding capacity and increasing sedimentation in rivers.
When forests are cleared for timber, agriculture, or urban development, the land loses its natural ability to absorb and slow water. This leads to faster runoff, higher peak flows in rivers and increased flood risk downstream.
Modern farming methods have transformed landscapes in ways that often increase flood risk.
Heavy farm machinery compacts soil, reducing its ability to absorb water. Compacted soil can have 90% less infiltration capacity than healthy soil, leading to increased surface runoff.
Artificial drainage systems installed to improve crop growth can rapidly channel water into streams and rivers, increasing downstream flood risk by concentrating water flow.
The types of crops grown and how fields are managed significantly impact flood risk:
Human interventions in river systems can both reduce and increase flood risk, sometimes with unintended consequences.
On 16 August 2004, the village of Boscastle in Cornwall experienced devastating flash floods after 200mm of rain fell in just 5 hours. Human factors that contributed to the severity included:
The flood destroyed 58 buildings, washed away 116 cars and required the rescue of 150 people. After the flood, management strategies included widening the river channel, installing larger bridges and creating upstream storage areas.
Human-caused climate change is altering precipitation patterns globally, often increasing flood risk:
These climate changes interact with other human activities to further amplify flood risk in many areas.
Understanding how human activities increase flood risk helps us develop better strategies to reduce it:
Incorporating permeable surfaces, green spaces and sustainable drainage systems into urban design.
Reforestation, protecting wetlands and promoting agricultural practices that improve soil health and water retention.
Flood-aware planning regulations, incentives for sustainable land management and integrated catchment management.
There's growing recognition that working with natural processes can effectively reduce flood risk:
These approaches often provide multiple benefits beyond flood management, including improved biodiversity, carbon storage and water quality.
Human activities have significantly altered natural water cycles and increased flood risk through:
By understanding these connections, we can develop more effective approaches to reduce flood risk while maintaining the benefits of development. The most successful strategies often combine engineered solutions with natural flood management and careful land use planning.
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