Reduced soil water-holding capacity and infiltration
Explanation
Forests act as natural sponges in the hydrological cycle. Vegetation cover regulates the movement of water through processes such as interception (catching rain on leaves), infiltration (water soaking into the ground), and transpiration. The removal of this cover fundamentally alters surface hydrology.
Option Analysis:
- Increased precipitation due to lack of trees is incorrect: Deforestation generally leads to reduced evapotranspiration, which can decrease local humidity and precipitation levels rather than increasing them. Floods are not caused by increased precipitation resulting from the lack of trees.
- Reduced soil water-holding capacity and infiltration is correct: Tree roots loosen the soil, creating macropores that facilitate water infiltration, while leaf litter absorbs impact and slows surface flow. Deforestation removes these mechanisms, leading to soil compaction and reduced water-holding capacity. Consequently, rainwater flows over the surface as runoff rather than seeping into the ground, causing rapid and intense flooding.
- Accelerated melting of glacial ice is incorrect: While deforestation contributes to global warming-which in turn accelerates glacial melting-this is an indirect, long-term climatic consequence. It is not the primary direct process linking deforestation to immediate flood incidence in a specific catchment area.
- Physical obstruction of river channels by timber is incorrect: Physical obstruction by timber may occur in specific instances, but it is not the fundamental hydrological process responsible for the widespread correlation between deforestation and increased flood frequency.
Key Takeaway: The primary link between deforestation and flooding is the loss of the soil's infiltration capacity, which dramatically increases surface runoff and reduces the time taken for water to reach river channels.