Chapter 5 Evaporation

Question 1

Until recently the interest of hydrologists in the atmosphere was restricted to processes related to

Answer 1

rainfall and evaporation

Question 2

The atmosphere was considered the domain of the meteorologist, who developed ……………………………………………………..to forecast the weather.

Answer 2

General Circulation Models (GCM)

Question 3

The integration of much better models for the simulation of the soil water balance such as ……………………….into the …………………………………

Answer 3

SWATRE

GCMs

Question 4

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

Answer 4

the atmospheric and terrestrial hydrological components of the earth system operate on different time and space scales.

Question 5

Traditionally hydrologists are interested in ………………………………… because…………………..

Answer 5

evaporation

it is an important component in many water balance studies and often considered as a loss.

Question 6

In irrigation water development projects an accurate assessment of …………………………………………………is a prerequisite for a proper design.

Answer 6

the crop water use

Question 7

Types of evaporation

Answer 7

1. Evaporation
2. Transpiration
3. Evapotranspiration

Question 8

latent heat of vaporization

Answer 8

The transfer of water in the liquid state into water vapour requires energy

Question 9

The amount of radiation that is available for ………………………………depends on the………………………………..

Answer 9

evapotranspiration

1. latitude,
2. atmospheric conditions (e.g. cloudiness),
3. reflection from the earth surface,
4. absorption by the atmosphere and
5. the storage in the ground (or water body)

Question 10

It is necessary for the process of evaporation to continue that the water vapour is ……………………………………………………..

Answer 10

removed from the evaporating surface

Question 11

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 …………………………….

Answer 11

diffusion and turbulent transport

Question 12

Evaporation is affected by:

Answer 12

1. The temperature
2. Humidity of the air
3. The roughness of the surface
4. The wind speed

Question 13

Moreover, for the process of transpiration,…………………………………………………………. and ………………………………………………………………play an important role.

Answer 13

the resistance to flow of water in the plant

the percentage of the soil covered by the crop

Question 14

For an evaporating surface consisting of bare soil or open water the factors include:

Answer 14

1. reflection coefficient
2. roughness of the surface
3. heat storage capacity For a cropped surface two additional factors play a role:
4. soil cover
5. crop resistance

Question 15

The atmospheric conditions affecting evapotranspiration comprise:

Answer 15

1. temperature
2. wind velocity
3. relative humidity
4. solar radiation

Question 16

Reflection coefficient or albedo for

Free water surface

Answer 16

0.06

Question 17

Reflection coefficient or albedo for

Grass

Answer 17

0.22-0.25

Question 18

Reflection coefficient or albedo for

Bare soil

Answer 18

0.10 - 0.30

Question 19

Reflection coefficient or albedo for

Fresh snow

Answer 19

0.90

Question 20

The transfer of water vapour from the ……………………………..into the atmosphere may be regarded as …………………………………….

Answer 20

evaporating surface

turbulent transport

Question 21

The transfer of water vapour from the evaporating surface into the atmosphere may be regarded as turbulent transport, except for ………………………………………….. known as …………………………….

Answer 21

a very thin layer at the surface known as the laminar sub-layer

Question 22

except for a very thin layer at the surface known as the laminar sub-layer, where the transfer is caused by

Answer 22

molecular diffusion

Question 23

The fraction of soil that is covered by the crop directly affects the

Answer 23

transpiration of the considered area.

Question 24

……………………………………of a cropped surface is usually ……………….than the ……………………of an open water surface

Answer 24

Transpiration

less

evaporation

Question 25

Transpiration of a cropped surface is usually less than the evaporation of an open water surface due to the

Answer 25

additional resistance to the flow of water in the plant and the transfer of water vapour through the stomata.

Question 26

…………………………………………….depends on the temperature

Answer 26

The saturation vapour pressure of the air

Question 27

…………………………………………………………………………………… is a function of the wind speed.

Answer 27

The aerodynamic resistance to water vapour transport

Question 28

……………………………………is very sensitive to the humidity of the air

Answer 28

Evaporation

Question 29

Evaporation is very sensitive to the humidity of the air and it ceases completely when the air becomes …………………………….

Answer 29

saturated with water vapour

Question 30

More shade, ……………….. evaporation

Answer 30

less

Question 31

when temperature rise ………………………………………………..

Answer 31

saturation vapor pressure rise

Question 32

when wind increase ……………………………..

Answer 32

evaporation increases

Question 33

When relative humidity increases ………………………………

Answer 33

evaporation decreases

Question 34

The latent heat of vaporization, L required for the transfer of water into vapour is, directly or indirectly, provided by

Answer 34

energy from the sun

Question 35

in the latent heat of vaporization the most dominant factor determining …………………………………………. is …………………………………..

Answer 35

the evaporation rate

solar radiation

Question 36

The actual evapo(transpi)ration becomes less than its………………… when ………………………………………………which does, of course, not apply for

Answer 36

potential value

water is not readily available

a free water surface

Question 37

The evaporation from a wet bare soil may, after a short while, reduce drastically when

Answer 37

desiccation of a thin top layer prevents a sufficient supply of water from below.

Question 38

The deviation of the actual evapotranspiration rate from its potential value for a cropped surface occurs

Answer 38

more gradually due to the larger depths over which the roots can take up the soil moisture.