Evapotranspirairon

Question 1

What are the three types of evapotranspiration

Answer 1

Open water evaporation
Wet canopy evaporation
Transpiration

Question 2

What are the different ways of assessing evapotranspiration

Answer 2

Evaporation pan

Pennman method

Question 3

Example of evaporation pan

Answer 3

Symons tank (Uk)

Question 4

Problem with evaporation tank

Answer 4

Smaller heat storage.

Higher advective transfers.

Question 5

How to solve the problems with evaporation pans

Answer 5

Correction by a pan coefficient I

Question 6

What is the penman method

Answer 6

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

Question 7

What is net radiation

Answer 7

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

Question 8

What is saturation deficit (Es-e)

Answer 8

How wet atmosphere is.

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

Question 9

What is wind speed (u)

Answer 9

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

Question 10

How to measure Es and e in pennman equation

Answer 10

Dry and wet bulb temp

Question 11

How to measure u in pennman equation

Answer 11

Anemoter

Question 12

How to measure Rn

Answer 12

Net radiometer

Question 13

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

Answer 13

Automatic weather station (AWS)

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

Question 14

Local weathering station

Answer 14

LECA hazelrigg automatic weather station

Question 15

What is the problem with pan evaporation rates

Answer 15

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.

Question 16

What is wet canopy evaporation measured by

Answer 16

Canopy water balance - what hits it and what gets beneath

Question 17

What is Pgross

Answer 17

Rainfall reaching canopy. Throughfall + stemfall is Pnet.

Pnet + Iloss

Question 18

What are the controlling factors of wet canopy evaporation

Answer 18

Rainfall intensity

Vegetation type

Question 19

What is rainfall intensity

Answer 19

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

Question 20

What is the difference in vegetation type

Answer 20

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

Question 21

How much precipitation do conifers intercept

Answer 21

20-40%

Question 22

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

Answer 22

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

Question 23

equarion to measure wet canopy evaporation

Answer 23

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

Question 24

How to measure wet canopy evaporation

Answer 24

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.

Question 25

How many throughfall plots in Borneo and why

Answer 25

500 bc it’s enormougjly variable through canopy

Question 26

How to collect stem flow

Answer 26

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

Question 27

How does transpiration work

Answer 27

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

Question 28

What reduces transpiration

Answer 28

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

Question 29

What is half the water in a catchment lost by

Answer 29

Transpiration as opposed to going to a river

Question 30

What are he controls of transpiration

Answer 30

Stomata loss and root absorption

Question 31

How to measure transpiration

Answer 31

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

Question 32

How does porometer work

Answer 32

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

Question 33

How does a sapflow sensor work

Answer 33

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

Question 34

How does lysimeter work

Answer 34

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

Question 35

What is the equation for lysimeter water balance

Answer 35

T = Pnet - Q +/- ^S

Drainage (out of lysimeter) +/- soil moisture

Question 36

How to measure soil moisture

Answer 36

Neutron probe to measure change in storage

Question 37

How to measure long term catchment water balance

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What is done to reduce errors in evaporation measurements

Answer 39

Modified pennman method - above canopy measurements.

Question 40

How to use modified penman method

Answer 40

Use meterolgical variables above the forest

Question 41

What is the impact of rainforest logging

Answer 41

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.

Question 42

What is one exception of precipitation being reduced in logged forests

Answer 42

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.