Crop coefficients can be greater than 1.00.
Ex: Corn 1.15
Then ETa=Kc *ETo, it seems to be ETa greater than ETo.
But ETo is the evaporative power of the amosphere. is it possible to go over that value?
Not necessary. If reference ET is equal to Potential evapotranspiration , Then your analogy may be true.
ET0 is actually a reference value, not the highest possible loss per unti surface. Leaf area index turbulence and leaf temperature can increase crop requirement above ET0, see http://www.fao.org/docrep/X0490E/x0490e0b.htm
There are some definitions you should know to answer your question. If the reference crop is grass (assumed crop height of 0.12 m, a fixed surface resistance of 70 s m-1 and an albedo of 0.23), the calculated ET is a grass reference ET (ETo) and if it is alfalfa crop, the value is for Alfalfa-reference evapotranspiration (ETr) (ETr = 1.2 x ETo). Both are references crops which means these values are the crop evapotranspiration under standard conditions (ETc) or some times called potential evapotranspiration (ETp) for the two crops. In case you utilize the FAO-Penman monteith as you stated in your question (kc x ETo) for a certain crop, then you calculate the ETc or ETp for this certain crop (e.g. corn). Actual evapotranspiration (ETa) of a crop represents the actual water consumption. Normally, ETa is equal to or less than ETc because the field is not under the standard conditions. Currently there are many publications regard to estimate ETa from remote sensing and installing devices such as eddy covariance tower or Lysimeter.
Back to your question and equation: Yes, Single or Dual crop coefficients for some crops are higher than 1 (e.g. Barley, Groundnut ... etc) and therefore ETc or ETp for a crop is higher than ETo.
If you would like to know further, you can read my works on ETa estimates or feel free to contact me:
Article Spatio-temporal performance of large-scale Gezira Irrigation...
Article Satellite-based evapotranspiration over Gezira Irrigation Sc...
Article Implications of non-sustainable agricultural water policies ...
Yes, Single or Dual crop coefficients for some crops are higher than 1 (e.g. Barley, Groundnut, oil palm, banana ... etc) and therefore ETc is higher than ETo.
Generalmente en la época de floración la Etc es mayor que Et0
Could we exceed ET_o (reference evapotranspiration)? Yes.
The easiest analogy I could think of is that a tall, old tree that covers a square with the dimensions of 5x5 meters needs a lot more water than alfalfa crop planted in the same area, the reason being that the tree has much more foliage and biomass. Even though ET_o is primarily used for farming plants and less often for calculating water requirements of trees, I find the comparison useful.
Yahampath Marambe yes i do like to add the statement that It isn't required. Your analogy may hold true if reference ET is equal to potential evapotranspiration. The actual water consumption of a crop is represented by its evapotranspiration (ETa). Because the field is not under standard conditions, ETa is usually equal to or less than ETc.
Dear Dr Yahampath Marambe . See the following useful RG link: Preprint Methods of Evapotranspiration