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Geog322 > evapotranspiration > Flashcards

evapotranspiration Flashcards

1
Q

evaporation

A

direct transfer of water from open water body/soil/ vegetation surfaces to atmo

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2
Q

how evaporation occurs

A

-water molecule move constantly
-some break away from surface VS other come back
-net evaporation = more molecule leaving surface than returning

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3
Q

2 controls of evaporation

A

-vapor pressure deficit
-energy

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4
Q

latent heat of vaporization

A

energy a water molecule needs to escape water surface
-source of energy -> mostly solar radiation

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5
Q

Vapor pressure deficit

A

Diff between how much moisture air CAN hold when saturated VS actual amount of moisture in air
VPD = es-ea

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6
Q

Relative humidity equation

A

RH = (ea/es)x100%

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7
Q

Dew point temperature

A

temp at which air starts to condensate (100% relative humidity)

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8
Q

Saturation vapor pressure (es)

A

max amount of moisture air can hold at given temp

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9
Q

Actual vapor pressure (ea)

A

actual amount of moisture air holds at air temp

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10
Q

equation for ea

A

ea = es x (RH / 100)

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11
Q

factors affecting evaporation

A

Vapor pressure diff between water surface & air
Temperature
Wind
Atmo pressure
Water Quality

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12
Q

Methods used for Estimating evaporation

A

-water budget equation
-energy budget method -> simplified version
-evapo pan measurements

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13
Q

Water budget method for evapo

A

Isolate Evapo from equation of water budget
Advantage: simple
Disadvantage: Difficult to estimate seepage loss & subsurface runoff AND unreliable

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14
Q

Energy budget method (full one)

A

Isolate energy used for evapo from equation
Advantage: most accurate
Disadvantage: difficult to estimate all terms/ equation must be simplified/ empirical formula used

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15
Q

Energy budget simplified equation

A

Rnet = lambda x E + H + G
Where, H is sensible heat transfer to air, G is heat conducted to ground, lambda is latent heat of vaporization

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16
Q

Rnet equation

A

Rnet = Rtotal x (1 - albedo)

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17
Q

assumptions of simplified energy method

A

Energy is limiting factor
Energy balance without water input

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18
Q

Evapo pan measurements issues

A

Overestimate evapo
-less heat storage capacity (small volume)
-heat transfer
-wind effects

19
Q

Solution to overestimation of evapo pan

A

Etrue = Cp x Epan -> use of pan coefficient

20
Q

+ and - of evapo pan measure

A

+ : simple
-: overestimate evapo
poor indicator of land/ lake evapor

21
Q

Transpiration

A

indirect transfer of water from root-stomatal system to atmo

22
Q

what drives water movement in plants

A

Energy difference -> from less negative moisture tension in soil to more negative tension in atmo

23
Q

Stomata

A

air opening allowing plant to exchange gas with atmo
open/close with diurnal effect & water tension

24
Q

Stomatal conductance

A

rate of gase exchange with air via stomata
-highest with crops
-many variables affect it
-strong relationship with transpiration

25
Q

Importance of transpiration

A

Plant-mediated diffusion of soil water to atmo
Primary leaf cooling mechanism under high radiation
pathway for nutrient uptake & matrix for chem reaction

26
Q

Evapotranspiration

A

summarize all process returning water to atmo in vapor forms

27
Q

Factor affecting transpiration

A

Temperature
solar radiation
wind
plant type
soil moisture

28
Q

phytometer

A

completely sealed contained with soil & plant growing in it -> measure transpi

29
Q

potometer

A

System connecting tube to plant stem to see speed & distance travel of air bubble in water tube -> transpi measurements

30
Q

Transpi VS Evapo VS interception with land cover type

A

At plant lvl: transpi > evapor
Forest: + interception, - evapo, + transpi
Agri field: - interception, + evapo, - transpi

31
Q

Ways to measure evapotranspiration

A

Lysimeter measurements
inflow-outflow measure (water-balance principle)
micrometeorological measures (Flux tower)
ET equation
Study of GW fluctuation

32
Q

Lysimeter conditions, + and -

A

condition: same soil & vegetation inside and outside tank
+: direct ET measure that are very precise
primary tool for evaluating weather effect on ET
-: difficult & expensive to construct
require careful operation and maintenance
primarily for research

33
Q

Eddy flux tower functioning, + & -

A

measure vertical transfer of water vapor & CO2 driven by convection moisture
+ : continuous measurement
dont disturb surface monitored
direct ecosystem lvl measures
-: expensive
require air turbulence
require flat terrain & homogenous vegetation
Gap-filling dataset is difficult
difficult to operate in remote location (e.g. trees breaking)

34
Q

PET

A

ET that would occur with no water limitation -> determined by weather and energy

35
Q

AET

A

actual evapo rate from any surface under prevailing conditions of moisture availability and radiative input -> determined by weather, energy AND water availability

36
Q

Comparing AET and PET

A

Always AET <= PET
-dry soil & other natural conditions: AET < PET
-open water body & over-saturated bare soil: AET = PET

37
Q

Reference crop evapotranspi (ETrc) conditions

A

well-watered grass
specific canopy resistance
specific albedo
completely shades ground

38
Q

Blaney-Criddle method

A

Only focus on temperature -> simplest

39
Q

Thornthwaite method

A

Applicable to arid areas
only need temperature data But indirect reference to radiative balance

40
Q

Penman model

A

Requires great amount of data
Strong physical knowledge
originally designed for free water surface
BUT ignores soil heat conduction

41
Q

Penman-Monteith model:

A

requires even more data
consider surface and atmo resistance
BUT consider vegetation canopy as one leaf

42
Q

Hargreaves method

A

Only requires air temperature and extraterrestrial radiation
Can get daily estimates
BUT for ETrc and underpredicts arid & windy conditions

43
Q

Hamon

A

Requires Temp, daylight hours and considers saturated vapor pressure

Geog322 (9 decks)

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