Evaporation is the process by which liquid water is transformed into water vapor through exposure to solar energy. It is an essential part of the water cycle. Evapotranspiration involves both evaporation from open water and transpiration through plant stomata, and is the total amount of moisture removed from vegetated land surfaces. Potential evapotranspiration represents the maximum amount that could be evaporated or transpired given sufficient available water, and is directly related to temperature conditions.

1. AS GEOGRAPHY
BRIEF REVISION
HYDROLOGY
01
EVAPORATION
EVAPOTRANSPIRATION

2. EVAPORATION
Evaporation is the process by which liquid water is transformed into
water vapour, which is a gas.

3. ESSENTIAL PART OF THE WATER CYCLE
Evaporation is an essential part of the water cycle.
The sun (solar energy) drives evaporation of water from oceans,
lakes, moisture in the soil, and other sources of water.

4. EVAPOTRANSPIRATION
In hydrology, evaporation and transpiration (which involves
evaporation within plant stomata) are collectively termed
evapotranspiration.
Evaporation of water occurs when the surface of the liquid is exposed,
allowing molecules to escape and form water vapor; this vapour can
then rise up and form clouds.
With sufficient energy, the liquid will turn into vapour.

5. POTENTIAL EVAPOTRANSPIRATION
In a nutshell, evapotranspiration is the total amount of moisture
removed by evaporation and transpiration from a vegetated land
surface.
Potential evapotranspiration is the amount of water that could be
evaporated or transpired from an area given sufficient water available.
Potential evapotranspiration is directly related to prevailing
temperature conditions.
The relationship between precipitation and potential
evapotranspiration for an area is represented by a soil moisture graph.

6. IN A NUTSHELL
Evaporation is water turning into water vapour – turning from a liquid
to a gas.
Transpiration is evaporation from plant leaves – plants and trees take
up water through their roots and transport it to their leaves where it
evaporates into the atmosphere.
Evapotranspiration is the process of evaporation and transpiration
together.
Potential evapotranspiration (PET) is the amount of water that could be
lost by evapotranspiration. Actual evapotranspiration is what actually
happens.

7. EXAMPLE
In a desert potential evapotranspiration is high (because heat
increases the amount of evaporation) but actual transpiration is low
(because there isn’t that much moisture in the first place).
Evapotranspiration stations at the
Amargosa Desert Research Site, Nevada.

8. EXAM QUESTION
Define evaporation.
ANSWER ON THE NEXT PAGE

9. EXAM ANSWER
Evaporation is the process by which water changes into a gas.