01 Why can deforestation in an upper watershed increase flooding downstream?
Answer and explanation
Correct answer: A. Infiltration decreases and runoff reaches downstream rapidly
Explanation: The governing hydrological concept is the effect of vegetation on infiltration, interception, and runoff. Forest canopies intercept rainfall, roots hold soil, leaf litter increases surface roughness, and porous soil allows more water to infiltrate and recharge groundwater. When forests are removed, these processes weaken. More rainwater flows quickly over the surface, carrying sediment into channels and increasing the volume and speed of downstream discharge. Thus option A is correct, although the size of the flood also depends on rainfall intensity, soil, slope, drainage, and channel conditions. Option B has no necessary connection with deforestation. Option C is not an immediate consequence of cutting trees in one watershed. Option D is false because deforestation does not stop rainfall. The key mechanism is faster runoff and lower infiltration.