Evapotranspiration

Question 1

What is evaporation

Answer 1

The process where water in liquid or solid state is transformed into a gas

Question 2

Who showed the driving force for evaporation?

Answer 2

John Dalton- molecules are constantly moving and evaporation occurs when more molecules are changing to the vapour phase then reverting back to a liquid.

Question 3

What is the latent heat of vaporization?

Answer 3

The amount of heat required to overcome the latent heat barrier and break through the water surface

Question 4

Latent heat of water?

Answer 4

540 cal/g at 100 degrees of solar radiation

Question 5

Transpiration?

Answer 5

Evaporation from vegetation

Question 6

Evapotranspiration?

Answer 6

Net amount of water evaporated from soil and transpired from plants

Question 7

Potential ET?

Answer 7

-The amount of water which could be evaporated or evapotranspired if moisture was not limiting.
-Evaporation from a free water surface is always at a potential rate

Question 8

Actual Evapotranspiration

Answer 8

Multiply the potential Evapotranspiration of the reference crop by the crop coefficient and the soil coefficient

Question 9

Average Evapotranspiration for Ontario

Answer 9

450 mm/year

Question 10

Reference Evapotranspiration

Answer 10

Rate at which water would be removed from soil and plant surfaces of a specific crop

Question 11

Open water Evapotranspiration

Answer 11

The rate at which water would be removed from from an open water surface

Question 12

Pan evaporation

Answer 12

-Rate at which water would be removed from a small container
-multiply by pan coefficient to get actual evaporation

Question 13

Factors influencing evaportranspiration

Answer 13

-Energy supply
-Meteorological conditions
-Evaporating surface
-Water quality

Question 14

What are some pros and cons associated with water budget equation?

Answer 14

-simple but not reliable
-complicated when snow is a huge factor
-good for feasibility studies
-good for long periods of time

Question 15

Field plots

Answer 15

-inventory of all inputs and outputs and change in storage
-Water table deep
-uses water budget equation

Question 16

Soil moisture depletion budget

Answer 16

-measuring changes in soil moisture over a period of time
-works when multiple measurements are taken to form an average, and depth of water table is greater than depth of root zone

Question 17

Tanks and Lysimeters

Answer 17

-small tank where crop grown under natural conditions
-uses water budget equation

Question 18

Energy balance method

Answer 18

-most complex method
-considers incoming energy from solar, geothermal, and other sources
-1 Langley (ly) = 1 cal/cm2

Question 19

Mass transfer method

Answer 19

-wind has a major effect on Evapotranspiration
-wind removes Vapor laden air by convection
-keeps boundary layer thin
-high rate of water transfer from liquid to vapour state
-wind is turbulent and connective diffusion is larger than molecular diffusion

Transport of water away from surface depending on
-humidy gradient above water
-wind speed across surface

Question 20

Thornthwaite Method

Answer 20

-requires minimal data
-empirical equation
-predicts monthly Evapotranspiration from temperature and latitude
-only applicable in the central US

Question 21

Reference surface

Answer 21

-need a reference surface to determine evaporation rates for other surfaces via crop and soil coefficients
-grass and alfalfa are good reference surfaces because the characteristics are well defined

Question 22

Interception

Answer 22

-rainfall on vegetation and trapped on surface
-eventually lost as ET
-form of depression storage