Question

Reference crop evapotranspiration (\(\text{ET}_0\)) is dependent on

• A. Climatic factor only
• B. Climatic factor and crop factor only
• C. Crop factor only
• D. Climatic, crop and soil factor only

Hint:

$\text{ET}_0$ = Atmospheric evaporative demand (Climatic factors only). $\text{ET}_c = K_c \cdot \text{ET}_0$ (incorporates Crop factor).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
FAO-56 defines reference crop evapotranspiration (\(\text{ET}_0\)) as the evapotranspiration rate from an extensive hypothetical green grass reference surface of uniform height (0.12 m), actively growing, completely shading the ground, and not short of water.
Key Formula or Approach:
\[ \text{ET}_c = K_c \times \text{ET}_0 \]

Step 2: Detailed Explanation:
By standard FAO definition:
- Reference Crop Evapotranspiration (\(\text{ET}_0\)): Represents the atmospheric evaporative demand and is governed solely by climatic parameters (solar radiation, air temperature, relative humidity, and wind speed).
- The biological characteristics of specific crops are incorporated through the crop coefficient (\(K_c\)).
- Soil moisture constraints are incorporated through the water stress coefficient (\(K_s\)).
Thus, \(\text{ET}_0\) itself depends exclusively on climatic factors.

Step 3: Final Answer:
Hence, \(\text{ET}_0\) is dependent on Climatic factor only, matching option (A).