Question

Evapotranspiration is typically expressed in which one of the following units?

• A. \(\text{mm}^3\)
• B. mm
• C. kg mass per second
• D. \(\text{mm}^2\)

Hint:

Evapotranspiration is the combined loss of water from the soil surface by evaporation and from plants by transpiration. Like rainfall, it is treated as a depth of water spread over an area.

Answer 1

The Correct Option is B

Step 1: Understand evapotranspiration.
Evapotranspiration is the total water lost from the land, both by evaporation from the soil and by transpiration from plants.

Step 2: Compare it to rainfall.
Just like rainfall, we think of this water loss as a depth of water spread evenly over the ground.

Step 3: Recall how rainfall is measured.
Rainfall is measured as a depth in millimetres, for example 5 mm of rain.

Step 4: Apply the same idea.
Since evapotranspiration is also a depth of water over an area, it is measured in the same unit, millimetres.

Step 5: Reject the wrong units.
Cubic mm and square mm are volume and area, and kg per second is a mass flow rate, none of which fit a depth.

Step 6: Conclusion.
Evapotranspiration is expressed in mm.
\[ \boxed{\text{mm}} \]