Chapter 5 Evaporation Flashcards
Until recently the interest of hydrologists in the atmosphere was restricted to processes related to
rainfall and evaporation
The atmosphere was considered the domain of the meteorologist, who developed ……………………………………………………..to forecast the weather.
General Circulation Models (GCM)
The integration of much better models for the simulation of the soil water balance such as ……………………….into the …………………………………
SWATRE
GCMs
The integration of much better models for the simulation of the soil water balance such as SWATRE into the GCMs is hampered by the problem that
the atmospheric and terrestrial hydrological components of the earth system operate on different time and space scales.
Traditionally hydrologists are interested in ………………………………… because…………………..
evaporation
it is an important component in many water balance studies and often considered as a loss.
In irrigation water development projects an accurate assessment of …………………………………………………is a prerequisite for a proper design.
the crop water use
Types of evaporation
- Evaporation
- Transpiration
- Evapotranspiration
latent heat of vaporization
The transfer of water in the liquid state into water vapour requires energy
The amount of radiation that is available for ………………………………depends on the………………………………..
evapotranspiration
- latitude,
- atmospheric conditions (e.g. cloudiness),
- reflection from the earth surface,
- absorption by the atmosphere and
- the storage in the ground (or water body)
It is necessary for the process of evaporation to continue that the water vapour is ……………………………………………………..
removed from the evaporating surface
It is necessary for the process of evaporation to continue that the water vapour is removed from the evaporating surface. This is a process of ………………………….. and …………………………….
diffusion and turbulent transport
Evaporation is affected by:
- The temperature
- Humidity of the air
- The roughness of the surface
- The wind speed
Moreover, for the process of transpiration,…………………………………………………………. and ………………………………………………………………play an important role.
the resistance to flow of water in the plant
the percentage of the soil covered by the crop
For an evaporating surface consisting of bare soil or open water the factors include:
- reflection coefficient
- roughness of the surface
- heat storage capacity For a cropped surface two additional factors play a role:
- soil cover
- crop resistance
The atmospheric conditions affecting evapotranspiration comprise:
- temperature
- wind velocity
- relative humidity
- solar radiation
Reflection coefficient or albedo for
Free water surface
0.06
Reflection coefficient or albedo for
Grass
0.22-0.25
Reflection coefficient or albedo for
Bare soil
0.10 - 0.30
Reflection coefficient or albedo for
Fresh snow
0.90
The transfer of water vapour from the ……………………………..into the atmosphere may be regarded as …………………………………….
evaporating surface
turbulent transport
The transfer of water vapour from the evaporating surface into the atmosphere may be regarded as turbulent transport, except for ………………………………………….. known as …………………………….
a very thin layer at the surface known as the laminar sub-layer
except for a very thin layer at the surface known as the laminar sub-layer, where the transfer is caused by
molecular diffusion
The fraction of soil that is covered by the crop directly affects the
transpiration of the considered area.
……………………………………of a cropped surface is usually ……………….than the ……………………of an open water surface
Transpiration
less
evaporation
Transpiration of a cropped surface is usually less than the evaporation of an open water surface due to the
additional resistance to the flow of water in the plant and the transfer of water vapour through the stomata.
…………………………………………….depends on the temperature
The saturation vapour pressure of the air
…………………………………………………………………………………… is a function of the wind speed.
The aerodynamic resistance to water vapour transport
……………………………………is very sensitive to the humidity of the air
Evaporation
Evaporation is very sensitive to the humidity of the air and it ceases completely when the air becomes …………………………….
saturated with water vapour
More shade, ……………….. evaporation
less
when temperature rise ………………………………………………..
saturation vapor pressure rise
when wind increase ……………………………..
evaporation increases
When relative humidity increases ………………………………
evaporation decreases
The latent heat of vaporization, L required for the transfer of water into vapour is, directly or indirectly, provided by
energy from the sun
in the latent heat of vaporization the most dominant factor determining …………………………………………. is …………………………………..
the evaporation rate
solar radiation
The actual evapo(transpi)ration becomes less than its………………… when ………………………………………………which does, of course, not apply for
potential value
water is not readily available
a free water surface
The evaporation from a wet bare soil may, after a short while, reduce drastically when
desiccation of a thin top layer prevents a sufficient supply of water from below.
The deviation of the actual evapotranspiration rate from its potential value for a cropped surface occurs
more gradually due to the larger depths over which the roots can take up the soil moisture.