LESSON 5 Flashcards
It’s the water returned to the air, from a liquid to gaseous state
Evaporation
Evaporation from plants
Transpiration
Combination of evaporation and transpiration
Evapotranspiration
Used interchangeably with evapotranspiration
Consumptive Use
It refers to the sum of evapotranspiration and water used by the plants for tissue building processes
Consumptive Use
Importance of Evapotranspiration
For water conservation
For determining irrigation requirements for crops
For determining water storage in reservoir
Factors affecting Evaporation
- Meteorological Factors
- Nature of the evaporating surface
- Effects of water quality
Meteorological Factors
Solar radiation directly affects temperature.
Evaporation is directly proportional to air temperature.
Vapor pressure affects the degree of air saturation.
Evaporation is fast in dry air.
Evaporation is directly proportional to wind speed.
TRUE OR FALSE
All surface exposed to precipitation are
potentially evaporating surfaces
True
TRUE OR FALSE
The larger the area exposed to evaporation, the slower the rate of evaporation.
False; Faster
Evaporation varies ____________ with salinity of water
Inversely
TRUE OR FALSE
Evaporation rate is faster in fresh water due to low vapor pressure.
False; High vapor pressure
For saturated soils, evaporation may be similar to that from an ____________. As soil moisture decreases, the rate of evaporation ___________.
open free-water surface,
also decreases
Helps in moisture conservation
because they decrease the rate of
evaporation.
Mulches
Measurement of Evaporation
Evaporation pan
Lysimeter or Evapotranspirimeters
In order to make a measurement that takes these factors into account, it is possible to physically isolate a portion of land from its surroundings and continuously weigh it to monitor changes in water content.
Lysimeter or Evapotranspirimeters
Methods of Determining ET
- Field Experimental Plots
- Soil Water Studies
- Integration Method
- Inflow-outflow method
the quantity of water applied in these plots is kept small to avoid deep percolation losses and surface runoff is measured
Field Experimental Plots
samples are taken at various depths in the root zone
Soil Water Studies
the water used by plants and evaporation from the water and soil surfaces are combined for the entire area involved
Integration Method
inflow into the area (precipitation), outflow from the area and change in groundwater level are evaluated
Inflow-outflow method
Categories of Methods of Predicting Evaporation and Evapotranspiration
- Mass transfer
2 Energy of Balance - Empirica Methods
water moves away from evaporating and transpiring surfaces in response to the combined phenomena of turbulent mixing of the air and the vapor pressure gradient
Mass transfer
requires measurements of wind and humidity at two or more elevations
Mass transfer
heat is required for evaporation of water,
so if there is no change in water
temperature, the net radiation or heat
supplied is a measure of evaporation
Energy balance
developed from experience and field research based on assumption that the energy available for evaporation is proportional to temperature
Empirical Methods
