Measuring Heat Flux and Evapotranspiration

Tom Chaplin, CEO of Tule, explains evapotranspiration, the process of water loss from crops through evaporation and transpiration. He distinguishes between reference and actual evapotranspiration, highlighting factors like canopy size and water stress. Methods to measure evapotranspiration include lysometers and aerodynamic techniques like eddy covariance and surface renewal. The energy balance in ecosystems is crucial, with energy from the sun either warming the air or vaporizing water. Tule uses the surface renewal technique to measure sensible heat flux, allowing for the calculation of latent heat flux and actual evapotranspiration.

What is the primary difference between actual and reference evapotranspiration?

• Actual evapotranspiration is the water used by a specific field, reference is for a well-watered lawn.

• Reference evapotranspiration is for specific fields, actual is for lawns.

• Actual evapotranspiration is for lawns, reference is for fields.

• Both are the same and used interchangeably.

Which factor does NOT affect evapotranspiration?

• Canopy size

• Weather conditions

• Water stress

• Soil color

What happens to evapotranspiration when a plant is water-stressed?

• It remains the same

• It decreases

• It increases

• It fluctuates randomly

How does a lysometer measure evapotranspiration?

• By measuring soil temperature changes

• By observing plant growth rates

• By weighing the water loss from a pot of plants

• By calculating the air humidity

What is the role of the sun in the energy balance of an ecosystem?

• It only warms the air

• It has no role in the energy balance

• It cools the ecosystem

• It provides energy that is absorbed by the ground or used to vaporize water

What is the latent heat flux in the context of evapotranspiration?

• The heat absorbed by the ground

• The energy used to vaporize water

• The heat lost to the atmosphere

• The energy used to warm the air

What is the main limitation of using eddy covariance for measuring sensible heat flux?

• It requires a large number of instruments

• It is too simple and lacks accuracy

• It can only be used in deserts

• It is expensive and requires frequent maintenance

Which method measures the vertical movement of heat out of an ecosystem?

• Satellite imaging

• Lysometer

• Surface renewal

• Eddy covariance

What does surface renewal focus on when measuring sensible heat flux?

• The color of the soil

• The number of eddies and the heat they carry

• The height of the plants

• The amount of rainfall

Why can't satellites measure airflow effectively?

• They are too close to the Earth's surface

• They are designed only for measuring temperature

• They are located in outer space

• They can only measure water vapor