Question

Given below are two statements:

Statement (I): Penman proposed an equation for evaporation from an open water surface based on a combination of energy balance and sink strength.

Statement (II): For converting PET into ET, suitable crop coefficients should be evolved for different crops, soils and climatic conditions and also for different stages of growth for the same crop.

In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Recall what the Penman equation combines and how PET is converted into actual crop water use.

Answer 1

The Correct Option is A

Step 1: Check each statement against the known background of the Penman equation and crop coefficient practice.

Step 2: Statement (I) is correct. Penman's 1948 equation for open water evaporation is a combination method, it blends the energy balance approach (net radiation driven evaporation) with the aerodynamic or mass transfer approach (sometimes called sink strength, related to wind and vapour pressure deficit) into a single formula.

Step 3: Statement (II) is correct. Potential evapo-transpiration is converted to actual crop evapo-transpiration using a crop coefficient, ET equals Kc times PET. Since water use differs by crop type, growth stage, soil and local climate, separate crop coefficients are worked out for different crops, different growth stages of the same crop, and different regions.

Step 4: Both statements are correct, so option 1 is the answer.