Question

The instrument which is used to measure evapotranspiration in the field condition is:

• A. Evaporimeter
• B. Current meter
• C. Lysimeter
• D. Pyrometer

Hint:

Don't confuse Evaporation with Evapotranspiration. An Evaporimeter (like a Class A pan) measures potential evaporation from a water surface, while a Lysimeter measures actual evapotranspiration from a soil and plant system.

Answer 1

The Correct Option is C

Step 1: Define Evapotranspiration (ET). Evapotranspiration (ET) is the combined process of water evaporation from soil surfaces and transpiration from plants, a crucial element of the hydrologic cycle.
Step 2: Analyze instrument functions.

• Evaporimeter (or Pan Evaporimeter): Quantifies evaporation rate from an open water surface. This provides an estimate, not a direct ET measurement from vegetated areas.
• Current meter: Measures water flow velocity in rivers or channels.
• Lysimeter: A device for measuring actual evapotranspiration from plants. It comprises a soil block with vegetation within a container, enabling measurement of water input (precipitation, irrigation) and output (drainage). The difference between input and output indicates ET.
• Pyrometer: Remotely measures temperature, particularly high temperatures, by detecting thermal radiation.

Step 3: Identify the correct instrument. Considering their respective functions, the Lysimeter is specifically designed for direct measurement of evapotranspiration in field conditions.