CROPWAT is a FAO software used for calculation crop water requirements. It includes a database of previously derived crop coefficients for common crops, also documented in FAO publication no. 56. If you have access to the necessary climate data (min. and max. temperatures, relative humidity, wind speed, solar radiation) for your site of interest, you can use CROPWAT to estimate reference crop evapotranspiration (ETo) which then you can use to calculate actual evapotranspiration of a specific crop by multiplying ETo by the crop coefficient.
However, if your goal is to actually determine (calibrate) a crop coefficient for a specific crop yourself, you would need to measure the actual crop evapotranspiration (ETr) by a direct method (lysimeter or micrometeorological methods like eddy correlation,Bowen Ratio/Energy balance, or scintillometry) and at the same time measure the standard climate variables mentioned above with an automatic weather station in order to determine the corresponding ETo. Crop coefficient Kc = ETr/ETo
Well if you are interested in estimation of actual evapo-transpiration for a large scale then it is expensive to use lysimeter or other eddy covariance measurement instruments. So could you let us know your spatial and temporal resolution and I personally believe that fitted model for particular area may vary. for Arid and sub-arid region SEBAL (surface energy balance algorithm ) is very suitable choice and could give you about 80% accuracy in estimating Actual ET. to apply SEBAL there are many ways and If I am not wrong then you can use ILWIS which has builtin algorithm or ERDAS. good luck!
Measuring crop coefficient and evapotranspiration is not difficult if you have a humidity and temperature sensor. Consumer products is enough to use determination.
http://www.jircas.affrc.go.jp/english/publication/highlights/2006/2006_10.html
you can applied CROPWAT. 8 software for this purposes . by using of this software and meteorologic data gathering of case study area . Crop evapotranspiration (ET0) and effective rainfall (Peff) were calculated using local temperature, humidity, sunlight, and rainfall data of Meteorological Organization. CROPWAT 8.0 software was applied to calculate crop evapotranspiration and effective rainfall.
To me, the easiest is to use the water balance within the crop root zone. By quantifying precipitation, irrigation, percolation, runnoff, change is soil moisture over a given time period, the your crop evaporation could be determined. Soil moisture could be sensed with the TDR or by thr traditional method of core sampling.
Regarding the use of the SEBAL model, you will need to have in-situ measurements in any case to calibrate/validate remote-sensing data for the model, in which case I recommend using scintillometry as mentioned before, as it can give you area-averaged ETr on about the same scale as the grid size of the model and any satellite images you may choose to use with SEBAL.
Dear friends Please ... How to calculate the crop coefficient evapotranspiration and water footprint of vegetables and other crops not in the database of the CropWat software?
cropwat is there for finding Eto. in cropwat we can enter data manually also. and for finding there use to be excel sheets available on google.
You can evaluate evapotranspiration by using CROPWAT software. The requirement for using this software is climate data(sum of precipitation, minimum and maximum temperature, humidity, wind speed)
Please read this book " Page 44 for crop coefficient and appendix II help you to evaluate evapotranspiration
by using software.
I see very interesting answers. However, I have a question related to this. I have measured ET only for few months after Jan but CROPWAT is asking to fill the Jan ET also. Should I calculate ETo (using PM equation) for all months to give input in this soft? Moreover, can I consider measured ET to estimate the Crop cofficients? However, I know my crop cofficients from the publication but I am not sure if this is valid for my region, therefore, I would like to validate it. Moreover, can I computr my actual ET for the crop using measured ET and multiply by Kc (after validation or from published research). Thank you.
but for cropwat u will need more data as rainfall, temperature , sun hours etc.
if u are having just temprature den Blaney cradle will do.
In the field, I think the easiest way is to use CROPWAT sofware, but is it possible to use satellites to measure evaporation?
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