I am building a model to see how climate change can affect crop yield. climate and crop yield are connected through the Hargreaves evapotranspiration equation. How can I express this equation in continuous form? It is reasonable to express the variation in daily mean temperature as a percentage of the variation in global mean temperature?
Dear Ruggiero;
I have fully read your model structure. I think you need to have a review on your model.
The first thing which I should notice is your first model:
Yi=ai*ET-bi
It's really a simple linear trend, no thing more. We have some stronger model for relationship of evapotranspiration - or maybe crop water - and yield. I send you one of the best "Crop yield response to water" which is prepared by FAO. I suggest you to read to read chapter 2 from page 6 to page 13.
The second is your evapotranspiration model which you named that as Hargreaves and Merkley. I think you used their book "Irrigation Fundamental", but the equation in page 71, which you use that for you model is originally the Hargreaves and Samani equation, which is presented in "Estimation of potential evapotranspiration" [1] which calculate potential evapotranspiration, not reference evapotranspiration. The method is a Radiation-Temperature Based method, and I should notice you that we have so different kind of methods to estimate potential evapotranspiration which are Temperature Based, Mass Transfer Based, Radiation Based and etc. If you want to use each one of theme I hope to be able to help you.
The last thing is your model, which is a growth model that change with time. I think you should have a review on your model!!
anyway, If you want to project climate change impacts on yield, you should notice other parameters that change too; for this I suggest you to read APSIM reference manual:
https://www.apsim.info/Documentation/TrainingManualsandResources/APSIMGeneralTrainingManual/ClimateChange.aspx
https://www.apsim.info/Documentation/TrainingManualsandResources/TrainingManual(SouthAsia)/Climatechangeprojections.aspx
And now, as an answer to your question, I should tell you that the climate projection in cordex project could project lots of parameters including potential evaporation which is being calculated using FAO Penman-Monteith equation in a fine spatial resolution and daily temporal.
Hope It helps.
Regards
Tabatabaei
[1]Hargreaves, G. H., & Samani, Z. A. (1982). Estimating potential evapotranspiration. Journal of the Irrigation and Drainage Division, 108(3), 225-230.
Thank you very much MuhammadReza Tabatabaei. If i may further ask you, do you know any good agricultural production function with water as an input?? I review my model as it was inconsistent in some part!
It's my pleasure to help you, but really I don't know what is your aim? what are you searching for?
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