Measurement, Radiation, Calculation

Question 1

Measurements Classification of methods:

Answer 1

1. Water balance methods
2. Micrometeorological methods
3. Remote sensing methods
4. Plant-physiological methods

Question 2

1. Water balance methods

Answer 2

evaporation ET in mm/Δt is determined as residuum from the water balance equation requiring precipitation, runoff and change in storage as known.

Question 3

2. Micrometeorological methods

Answer 3

latent heat lET in W/m2 is obtained based on the energy balance equation; direct methods measures lET directly (e.g. Eddy covariance method); indirect methods measure other variables related to IET (e.g. Flux-Profile or Bowen Ratio Energy Balance methods)

Question 4

3. Remote sensing methods

Answer 4

also based on energy balance; estimation of all terms leaving lET as unknown

Question 5

4. Plant-physiological methods

Answer 5

determines transpiration T;

measuring sap flow or gas exchange directly at the plants

Question 6

Radiation

Answer 6

Net radiation
=
Short wave radiation
\+
Long wave radiation

Question 7

Calculation

Answer 7

Potential Evaporation (ETP):

• Penman
• FAO – reference crop evaporation

Actual Evaporation (ETR):
- Penman - Monteith

Evaporation from open water:
- Penman