What are the factors influencing open water evaporation? How many methods are available and what are the factors influencing their estimation in open water evaporation?
- Supply of energy (solar radiation)
- Ability to transport the vapour away from the evaporation surface (wind velocity and specific humidity)
What are the limitations in combined method for open water evaporation estimation?
- changes in heat storage over time in the water body are not significant
- vapour transfer coefficient, B – need to be locally fitted with meteorological data
When Priestley-Taylor equation gives better estimation of open water evaporation?
For large areas when energy balance considerations largely govern the evaporation rate
What is evapotranspiration (ET), and what are the factors influencing ET?
- ET = land surface evaporation + vegetation transpiration
- Again, influenced by energy supply and vapour transport
Define the following: Pan evaporation (Ep), Potential evapotranspiration (PET), Reference crop evapotranspiration (ET0), Actual evapotranspiration (AET).
- Ep = defined experiment of a pan filled with water in order to replicate nearby open water evaporation.
- PET = Evapotranpiration that would occur from another well vegetated surface under existing atmospheric condition and when moisture supply is not limiting
- ET0 = Rate of ET from an area planted with a specific crop (grass or alfalfa), where water availability is not a limiting factor
- AET = Evapotranspiration that occurs under actual soil, ground-cover, and water-availability conditions