Lecture 5 - Evapotranspiration Flashcards
What is evapotranspiration?
Combination of evaporation and transpiration
How does water move during transpiration?
from soils through roots, stems, branches, to leaves
What do leaves have? Explain.
stomata, which are openings to the atmosphere. they contain h2o so that co2 can dissolve in water and be used by the plant
What kind of process is transpiration? What drives this process
physical, vapour pressure deficit between stomata and air
What is a critical paramter in long term water budgets?
evaporation and transpiration (ET)
What are the annual amounts of ET in NS?
300-600 mm/yr
What is Potential Evapotranspiration (PET)?
maximum rate of water loss from land surface if water is unlimiting
What is Reference Crop Evapotranspiration (ETo)?
maximum rate of water loss from land surface with specific vegetation if water is unlimiting
What is Actual Evapotranspiration (AET or ETa)?
actual rate of water loss from land surface with specific vegetation acccounting for water availability/use
What is Lake Evaporation (EL)?
rate of water loss from an open water surface
What is Latent Heat Exchange?
heat loss associated with phase change
What is Sensible Heat Exchange?
heat exchange related to a change in temperature of a substance
What are some direct measurement approaches?
water balances, evaporation pans, lysimeters
Explain lysimeters.
micro or mesoscale systems containing a defined volume/surface area of soil and plants, weighed at regular intervals to measure water loss
What is the Penman Combination Method?
combination of mass-transfer and enery balances to derive an expression that doesn’t require surface temperatures
What are the assumptions for the Penman Combination Method?
no heat exchange with the ground, no water advected energy, no change in heat storage
What is the Priestly-Taylor Method?
proposes that the aerodynamic term in the Penman Combination equation is approx 30% of the energy term
What does Thorwaite’s Method do?
Predicts monthly potential evapotranspiration based solely on air temperature
