Lecture 5 Flashcards
what is evapotranspiration
the combination of evaporation and transpiration
what is transpiration
when water moves from soils to the roots stems branches and leaves, the leaves have openings to the atmosphere called stomata.
is transpiration a metabolic process?
no, it is a physical process caused by a vapour pressure deficit between the stomata and air
What is and ET in NS
300-600 mm/yr
What is potential evapotranspiration
maximum rate of water loss from land surface if water is unlimiting
what is reference crop evapotranspiration
the maximum rate of water loss from land surface with specific vegetation accounting for water availability/use
what is lake evaporation
rate of water loss from an open water source
what are some ET estimation approaches
direct measurement
energy balance
aerodynamic
combination
what is latent heat exchange
evaporation * density of water * latent of vaporization
LE=Epwlv
(heat loss associated with phase change)
what is sensible heat exchange
sensible heat transfer coefficient * wind speed *( Temp of surface - Temp of air)
Hs=Khu(Ts-Ta)
(heat change related to the change in temperature of a substance)
change in storage =
Inputs - Outputs
water balance for a lake
S = P + R +/- G - E - W - O
what are the two direct measurement approaches mentioned in lecture
evaporation pans and lysimeters
how do evaporation pans work
you just put on a standardized pan into the sun and see how much water evaporates
what is a lysimeter
an evaporation pan put with plants and soil and stuff in it, it can be wieghed at regular intervals to measure water loss. (micro or mesoscale systems, defined volume/surface area of soil and plants)
what are the assumptions of penman combination method
no heat exchange with the ground
no water advected energy
no change in heat storage
priestly taylor method assumptions
(we use this one)
no heat exchange with ground
no water advected energy
no change in heat storage
aerodynamic term is 30% of the energy term
what kind of method is thornthwaites method
an empirical equation for monthly potential evapotranspiration
what kind of method is hargreaves equation
empirical equation for PET
