Changes to Flood Behavior
- Floods are dynamic events shaped by natural processes and human activities.
- Understanding how these factors interact is crucial for managing flood risks and protecting communities.
Urbanization: Impermeable Surfaces and Increased Runoff
- Imagine a city during a heavy rainstorm. Water cascades off rooftops, rushes down streets, and pools in low-lying areas.
- Why does this happen more in urban areas than in natural landscapes?
- The answer lies in impermeable surfaces.
- Surfaces that do not allow water to infiltrate into the ground, such as roads, pavements, and buildings.
- Increased Runoff: Water that would naturally soak into the ground is forced to flow over the surface, increasing the volume of runoff.
- Higher Peak Discharge: More water reaches rivers and streams quickly, raising the peak discharge and increasing flood risk.
- Shorter Lag Time: The time between peak rainfall and peak discharge is reduced, giving less warning before floods occur.
In a forested area, rainwater is absorbed by soil and vegetation, reducing runoff. In contrast, a city with extensive concrete surfaces channels rainwater directly into storm drains and rivers, overwhelming the system.
NoteUrban hydrographs typically show a steeper rising limb, higher peak flow, and shorter lag time compared to rural hydrographs.
Deforestation: Reduced Interception and Infiltration
- Forests play a vital role in regulating the hydrological cycle.
- When trees are removed, the landscape's ability to manage water is significantly altered.
- Reduced Interception: Without tree canopies to catch rainfall, more water reaches the ground, increasing surface runoff.
- Lower Infiltration: Tree roots help maintain soil structure, promoting infiltration. Deforestation compacts soil, reducing its ability to absorb water.
- Higher Peak Flows: More water enters rivers quickly, raising peak discharge and flood risk.
It’s a common misconception that deforestation only affects local areas. In reality, it can disrupt entire watersheds, increasing flood risks downstream.
