# Evapotranspirairon Flashcards

1
Q

What are the three types of evapotranspiration

A

Open water evaporation
Wet canopy evaporation
Transpiration

2
Q

What are the different ways of assessing evapotranspiration

A

Evaporation pan

Pennman method

3
Q

Example of evaporation pan

A

Symons tank (Uk)

4
Q

Problem with evaporation tank

A

Smaller heat storage.

5
Q

How to solve the problems with evaporation pans

A

Correction by a pan coefficient I

6
Q

What is the penman method

A

3 factors control evaporation.
Net radiation, saturation vapour pressure, wind speed.
E = aRn + b(Es-e)u

7
Q

A

Balance of energy of what’s coming from sun and out from earth or water surface Rn

8
Q

What is saturation deficit (Es-e)

A

How wet atmosphere is.

Saturation vapour pressure (holding capacity of the air) take maximum vapour pressure of air

9
Q

What is wind speed (u)

A

Wind blows away wet air exchanging for dry air increasing wind speed turbulence

10
Q

How to measure Es and e in pennman equation

A

Dry and wet bulb temp

11
Q

How to measure u in pennman equation

A

Anemoter

12
Q

How to measure Rn

A

13
Q

What equipment is used to measure all the components of penmans equation

A

Automatic weather station (AWS)

Has wind vane, anemometer, wet and dry bulbs, net radiometer

14
Q

Local weathering station

A

LECA hazelrigg automatic weather station

15
Q

What is the problem with pan evaporation rates

A

Used saturation deficit, wind speed and net radiation to estimate open water evaporation at Hazelrigg. Says rate is 2mm. Before evaporation pan correction, it says about 3mm a day which is over estimation and needs to be corrected by taking 1 off.

16
Q

What is wet canopy evaporation measured by

A

Canopy water balance - what hits it and what gets beneath

17
Q

What is Pgross

A

Rainfall reaching canopy. Throughfall + stemfall is Pnet.

Pnet + Iloss

18
Q

What are the controlling factors of wet canopy evaporation

A

Rainfall intensity

Vegetation type

19
Q

What is rainfall intensity

A

How fast it’s raining and size of drops. Short period of big raindrops.

20
Q

What is the difference in vegetation type

A

In tropical rainforests you can lose between 20-10% but in Uk grassland it’s less than 10% bc grass is hard to measure.

21
Q

How much precipitation do conifers intercept

A

20-40%

22
Q

Why do we have largest rates of wet canopy evaporation from UK conifers

A

Because it rains at low intensity for a long time and is usually windy

23
Q

equarion to measure wet canopy evaporation

A

Iloss = PPT above canopy - throughfall (Pgross) nd stemflow (Pnet)

24
Q

How to measure wet canopy evaporation

A

Canopy rain gauge but complicated.
Mast that goes to top of tree with a funnel to see what’s received by canopy.
Underneath canopy are volumetric rain gauges.

25
Q

How many throughfall plots in Borneo and why

A

500 bc it’s enormougjly variable through canopy

26
Q

How to collect stem flow

A

Collect from stem and put in a huge rain gauge tipping bucket

27
Q

How does transpiration work

A

Plants need co2 through stomata and in opening them leak water. So take water up through root and out through stomata.

28
Q

What reduces transpiration

A

Guard cell shuts off stomata and will try to take up water through soil which reduces transpiration

29
Q

What is half the water in a catchment lost by

A

Transpiration as opposed to going to a river

30
Q

What are he controls of transpiration

A

Stomata loss and root absorption

31
Q

How to measure transpiration

A

Porometer (leaf scale)
Sapflow sensor (tree scale)
Lysimeter water balance (few plant scale)
Long term catchment water balance (regional scale)

32
Q

How does porometer work

A

Clamp leaf in jaw and water evaporates from leaf into chamber then measure humidity in chamber

33
Q

How does a sapflow sensor work

A

Using cooling effect of moving water past two sensors to estimate speed of sap going up tree. Generally the amount going up is equal to amount going out the top

34
Q

How does lysimeter work

A

Trying to work out transpirational losses from grassland. Modified water balance equation

35
Q

What is the equation for lysimeter water balance

A

T = Pnet - Q +/- ^S

Drainage (out of lysimeter) +/- soil moisture

36
Q

How to measure soil moisture

A

Neutron probe to measure change in storage

37
Q

How to measure long term catchment water balance

A

The same equation as lysimeter water balance. Across catchment if we integrate the rain gauges and measure discharge coming out it leaves evaporation and change in storage

38
Q

Problem with assuming everything out of catchment is going into the river or sky

A

Basin leakage through deep seepage and channel underflow so you grossly inflate evaporation estimate. so really it’s E+P-Q plus or minus error

39
Q

What is done to reduce errors in evaporation measurements

A

Modified pennman method - above canopy measurements.

40
Q

How to use modified penman method

A

Use meterolgical variables above the forest

41
Q

What is the impact of rainforest logging

A

We cut off evaporation and there is less WCE and transpiration so big decrease.
Small reduction in precipitation but not by much.
Large increase in Q.

42
Q

What is one exception of precipitation being reduced in logged forests

A

Cloud forests as they strip water out of clouds. Very small amount of them but in Hawaii cloud forest 40% of import is water being stripped from clouds.