ETc is calculated as which formula?

ETc is calculated as which formula?

• A. ETc = ETo × Kc
• B. ETc = ETo + Kc
• C. ETc = ETo − Kc
• D. ETc = Kc ÷ ETo

Answer: (A)

The concept here is that actual crop water use is the reference evapotranspiration scaled by a crop-specific coefficient. The crop coefficient (Kc) adjusts the baseline ETo to reflect the particular crop, its growth stage, and canopy cover. Therefore, ETc is obtained by multiplying the reference evapotranspiration by the crop coefficient: ETc = ETo × Kc. This makes sense because Kc acts as a multiplier, indicating how much of the reference rate the crop actually uses. If Kc is above 1, the crop uses more water than the reference; if below 1, it uses less. For example, with ETo = 6 mm/day and Kc = 0.95, ETc ≈ 5.7 mm/day. The Kc values are unitless and vary with crop type, growth stage, and management. Adding, subtracting, or dividing would not reflect how crop water use scales relative to the reference, so those operations don’t produce the correct ETc.

The concept here is that actual crop water use is the reference evapotranspiration scaled by a crop-specific coefficient. The crop coefficient (Kc) adjusts the baseline ETo to reflect the particular crop, its growth stage, and canopy cover.

Therefore, ETc is obtained by multiplying the reference evapotranspiration by the crop coefficient: ETc = ETo × Kc. This makes sense because Kc acts as a multiplier, indicating how much of the reference rate the crop actually uses. If Kc is above 1, the crop uses more water than the reference; if below 1, it uses less.

For example, with ETo = 6 mm/day and Kc = 0.95, ETc ≈ 5.7 mm/day. The Kc values are unitless and vary with crop type, growth stage, and management.

Adding, subtracting, or dividing would not reflect how crop water use scales relative to the reference, so those operations don’t produce the correct ETc.