Question

Given below are two statements, one is labeled as Assertion (A), and the other one is labelled as Reason (R).
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.
In light of the above statements, choose the most appropriate answer from the options given below:

• 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:

The protective effect of canopy cover ($C$-factor) is expressed exponentially as $C = e^{-b \cdot \% \text{cover}}$, which shows that even small increases in vegetative cover can significantly reduce soil erosion.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Soil loss via water erosion depends on rainfall erosivity, soil erodibility, topography, and cover management factors, as described by the Universal Soil Loss Equation (USLE).

Step 2: Detailed Explanation:
- Assertion (A) is incorrect: The relationship between soil erosion and vegetative ground cover is highly non-linear.
Erosion rates typically decrease exponentially or sigmoidally as vegetative cover increases.
This non-linear relationship is due to canopy storage, interception, and surface roughness effects.
- Reason (R) is correct: The rainfall erosivity factor ($R$-factor in USLE) is calculated as:
\[ R = E \cdot I_{30} \] where $E$ is the total kinetic energy of the rainstorm and $I_{30}$ is the maximum 30-minute rainfall intensity.

Step 3: Final Answer:
Assertion (A) is incorrect, but Reason (R) is correct.