Question

Consider the following for Crop Evapotranspiration estimation approaches A. Modified Blaney-Criddle method is only temperature based B. Modified Penman Monteith method requires more climate data C. Thornthwaite method is based on temperature data D. Crop coefficient is multiplied to get reference evapotranspiration by Pan evaporation method E. Radiation method requires air temperature and sunshine radiation Choose the correct answer from the options given below:

• A. A, B, D Only
• B. B, D, E Only
• C. A, C, E Only
• D. B, C, E Only

Hint:

Important ET estimation methods:
• Thornthwaite \(\rightarrow\) Temperature based
• Penman-Monteith \(\rightarrow\) Requires multiple climatic data
• Radiation method \(\rightarrow\) Uses radiation and temperature
• Pan evaporation: \[ ET_0 = K_p \times E_{pan} \] Memory Trick: \[ \boxed{ \text{“Penman needs many parameters”} } \]

Answer 1

The Correct Option is D

Concept: Crop evapotranspiration estimation is one of the most important topics in irrigation engineering and hydrology. Different empirical and physically based methods are available to estimate evapotranspiration depending on:
• Climatic data availability
• Required accuracy
• Crop type
• Regional conditions Some methods are temperature based while others require multiple climatic parameters such as:
• Solar radiation
• Wind speed
• Relative humidity
• Sunshine duration The question asks us to identify the correct statements regarding evapotranspiration estimation methods.

Step 1: Analyzing Statement A. Statement A says: \[ \text{“Modified Blaney-Criddle method is only temperature based”} \] This statement is incorrect. The original Blaney-Criddle method primarily uses:
• Temperature
• Daylight hours However, the Modified Blaney-Criddle method also incorporates:
• Humidity
• Wind effects
• Sunshine Thus it is not purely temperature based. Hence: \[ \boxed{\text{Statement A is incorrect}} \]

Step 2: Analyzing Statement B. Statement B says: \[ \text{“Modified Penman Monteith method requires more climate data”} \] This statement is correct. The Penman-Monteith method requires:
• Temperature
• Relative humidity
• Wind speed
• Solar radiation Therefore it is a data-intensive method. Hence: \[ \boxed{\text{Statement B is correct}} \]

Step 3: Analyzing Statement C. Statement C says: \[ \text{“Thornthwaite method is based on temperature data”} \] This statement is correct. The Thornthwaite method estimates evapotranspiration mainly using: \[ \boxed{\text{Mean monthly temperature}} \] Hence: \[ \boxed{\text{Statement C is correct}} \]

Step 4: Analyzing Statement D. Statement D says: \[ \text{“Crop coefficient is multiplied to get reference evapotranspiration by Pan evaporation method”} \] This statement is incorrect. Crop coefficient is multiplied with reference evapotranspiration to obtain crop evapotranspiration: \[ ET_c = K_c \times ET_0 \] In pan evaporation method: \[ ET_0 = K_p \times E_{pan} \] where:
• \(K_p\) = pan coefficient
• \(E_{pan}\) = pan evaporation Thus crop coefficient is not used to determine reference ET from pan evaporation. Hence: \[ \boxed{\text{Statement D is incorrect}} \]

Step 5: Analyzing Statement E. Statement E says: \[ \text{“Radiation method requires air temperature and sunshine radiation”} \] This statement is correct. Radiation methods depend mainly upon:
• Solar radiation
• Temperature Hence: \[ \boxed{\text{Statement E is correct}} \]

Step 6: Identifying correct statements. Correct statements are: \[ B,\; C,\; E \] Incorrect statements are: \[ A,\; D \] Therefore the correct option becomes: \[ \boxed{ (D)\ B,\; C,\; E\ Only } \] Final Conclusion: The correct evapotranspiration estimation statements are: \[ \boxed{ B,\; C,\; E } \] Hence the correct answer is: \[ \boxed{ (D)\ B,\; C,\; E\ Only } \]