Question

Assertion (A): The effective rainfall erosion index of a given area is linearly proportional to the percentage of ground that is not covered by vegetation.
Reason (R): The rain erosion index includes both the kinetic energy of rain and the maximum 30-minute rain intensity.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
• C. (A) is correct but (R) is not correct.
• D. (A) is not correct but (R) is correct.

Hint:

Always evaluate logical connections in assertion-reason type questions independently of correctness.

Answer 1

The Correct Option is B

Both statements are individually true. However, the rain erosion index is a measure of erosivity and is not directly proportional to vegetation cover. Vegetation affects erosion but not through the definition of the index.

Answer 2

Conceptual check of each statement independently:
In the Universal Soil Loss Equation framework, the rainfall erosion index (commonly \( EI_{30} \)) is defined purely from a storm's rainfall characteristics: \[ EI_{30} = E \times I_{30} \] where \( E \) is the total kinetic energy of the storm and \( I_{30} \) is the maximum 30-minute intensity. This makes Reason (R) a factually correct definition. Separately, field studies show that as the percentage of bare, unvegetated ground increases, measured soil loss for a given storm rises in a roughly linear fashion, so Assertion (A) is also observed to be true. However, notice that (R) explains how erosivity itself is calculated from rainfall energy and intensity alone, with no vegetation term appearing anywhere in that formula. Therefore, while both statements are correct, (R) cannot be the explanation for why (A) holds.