Untitled Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the main factor required for the evaporation process to occur?

Presence of adequate nutrients

Constant water pressure

High vegetation cover

Source of energy to vaporize the liquid water (correct)

Which of the following correctly describes transpiration?

It involves the release of water vapour through stomata in plants (correct)

It is a process solely dependent on soil moisture

It is a function of atmospheric pressure alone

It requires low light intensity and wind

What does the term 'evapotranspiration' refer to?

Just the theoretical potential moisture loss

Evaporation from ocean surfaces only

The water lost from plant transpiration and soil evaporation (correct)

The total moisture retained in plant tissue only

Which environmental factor does NOT directly affect transpiration in plants?

Soil pH level Signup and view all the answers

Which device is used to measure the rate of transpiration?

Potometer Signup and view all the answers

What is the definition of potential evapotranspiration (PET)?

Theoretical moisture loss possible under ideal conditions Signup and view all the answers

Which factor does NOT influence evaporation?

Leaf area of surrounding plants Signup and view all the answers

The vapour pressure of water at the evaporating surface compared to that of the surrounding air is known as what?

Evaporation gradient Signup and view all the answers

What does effective evapotranspiration (EET) specifically measure?

The moisture loss from soil due to evapotranspiration Signup and view all the answers

Which method is NOT typically used to measure evapotranspiration?

Temperature increase method Signup and view all the answers

In the calculation of evapotranspiration (ET), what does the symbol 'S' represent?

Increase or decrease in storage of soil moisture Signup and view all the answers

Which factor does the crop coefficient (KC) directly influence?

Evapotranspiration rate of reference crops Signup and view all the answers

What is the role of a lysimeter in studying evapotranspiration?

To isolate a volume of soil hydrologically Signup and view all the answers

What does the formula ET = P + (I - D) + S represent?

Calculation of evapotranspiration from various water sources Signup and view all the answers

In the formula Rn - G - H = λET, what do Rn, G, and H stand for?

Net surface radiation, Ground heat flux, Sensible heat flux Signup and view all the answers

How can satellites contribute to understanding evapotranspiration?

By mapping infrared heat to distinguish cool and warm surfaces Signup and view all the answers

Study Notes

Evaporation

Evaporation is the process of a liquid changing into a gas.
Water changes to vapor through the absorption of heat.
Evaporation is a fundamental component of the hydrological cycle.
Key requirements for evaporation:
- A source of energy to vaporize the liquid water (solar or wind)
- A gradient of concentration between the evaporating surface and the surrounding air.
Evaporation is a function of the differences in vapour pressure of the water and the vapour pressure of the air.
Factors affecting evaporation:
- Degree of saturation of the surface
- Temperature of the surface and air
- Humidity
- Wind velocity
- Vegetation cover

Transpiration

Transpiration is the process by which water vapor leaves the living plant body and enters the atmosphere.
Involves continuous flow of water from soil into a plant and out through stomata (leaves) to the atmosphere.
Transpiration is essentially an evaporation process.
Transpiration ratio represents the amount of water transpired to produce a unit weight of dry matter.
Factors affecting transpiration:
- Climate:
  - Light intensity
  - Atmospheric vapor pressure
  - Temperature
  - Wind
- Soil:
  - Availability of water
- Plant factors:
  - Extent and efficiency of the root system
  - Leaf Area
  - Leaf arrangement and structure
  - Stomatal behavior

Evapotranspiration

Evapotranspiration (ET) is the quantity of water transpired by plants during growth or retained in plant tissue, plus the moisture evaporated from the surface of the soil and vegetation.
Accounts for the movement of water from sources such as soil, canopy interception, and water bodies, to the air.
Potential evapotranspiration (PET) is the theoretical amount of moisture that could be lost from the surface to the atmosphere if it were available.
Effective evapotranspiration (EET) is the actual amount of water lost due to evapotranspiration from the soil along with actively growing plants or crops.
- Depends on plant and soil characteristics, and upon the amount of available water in the soil.

Measuring Evapotranspiration

Methods for measuring evapotranspiration:
- Lysimeter experiment
- Field experimental plots
- Soil moisture depletion studies
- Water balance/budget method
- Eddy covariance
- Using US-open pan evaporimeter
- Energy balance

Lysimeter

Lysimeter: a device where a volume of soil planted with vegetation is located in a container to isolate it hydrologically from the surrounding soil.
Consists of a weighing device and a drainage system, which allow continuous measurement of excess water and draining below the root zone and plant water use, hence evapotranspiration.
The amount of water lost by evapotranspiration is calculated by the difference between the weight of the lysimeter before and after precipitation input.

Direct Methods for Measuring Evapotranspiration

Direct methods involve measuring fast fluctuations of vertical wind speed, which are correlated with fast fluctuations in atmospheric water vapor density.
Directly estimate the transfer of water vapor (evapotranspiration) from the land (or canopy) surface to the atmosphere.

Formulas for Calculating Evapotranspiration

Water balance method:
ET = P – Q – S – ΔD where:
- ΔS = watershed storage variation (mm): Send – Sbeginning
- P = Precipitation (mm)
- Q = Stream flow (mm)
- ΔD = Seepage out – seepage in (mm)
- ET = evaporation and transpiration (mm)
Energy balance method:
Rn - G - H = λET where:
- Rn : Net surface radiation flux density (Wm-2)
- G : Ground heat flux density (Wm-2)
- H : Sensible heat flux density (Wm-2)
- λET : Latent heat flux density (Wm-2)
- λ : Latent heat of vaporization of water (Jkg-1)

Temperature and Evapotranspiration

When a surface evaporates, it loses energy and cools itself.
This cooling can be observed from space.
Satellites can map the infrared heat radiated from Earth, differentiating cool surfaces from warm surfaces.