Here is the FAO Dependable Rain Method to computes MONTHLY effective rainfall
http://www.researchjournal.co.in/upload/assignments/8_109-115.pdf
Pe = 0.8 P - 25 if P > 75 mm/month
Pe = 0.6 P - 10 if P < 75 mm/month
Where Pe is the monthly effective rainfall and P is the monthly rainfall
If I want to use the same formula to compute DAILY rather than Monthly Rainfall, can I do that?
DailyPe = 0.8 DailyP - 25 if daily P >2.5mm/day (or 75 mm/30 days)
DailyPe = 0.6 DailyP - 10 if daily P < 2.5mm/day (or 75mm/30 days)
Where DailyPe is the daily effective rainfall and DailyP is the daily rainfall.
Hi Daniel
I also doing this type of study. I think you have to follow some kind of simulation model. FAO method absolutely valid only monthly data. Will do something together. Ofcouse this is a challenge for me as well.
Pe can be defined as the volume or depth of precipitation that reaches the mineral soil. The daily effective rainfall, Pe, is the difference between P-I; where P = gross precipitation and I = rainfall interception loss. Lets say, for example, in corn field, P = 13 mm and I = 3 mm; then Pe = 13-3 = 10 mm. This assessment assumes Pe is the volume or depth of precipitation that reaches the mineral soil. But you need to have information on I as it varies with crop type, age, density, etc; as well as with forest type, rianfall depth, intensity, duration, and climatic conditions. There is usually some information on interception loss in many hydrological reports or books.
Pe can also be defined as the effective precipitation to be transformed into crop productivity. Then Pe = P -I-L; where L = losses to evporation and drainage.A good unversal coefficient is 75% for L. Then Pe = (13-3)*0.75 = 7.5 mm. Again L is a function of crop, precipitation and climatic features.
Hope this information clarifies your concerns
Kind Regards
Sincerely
Jose Navar, Ph.D
You can look at page 66 of this book:
https://books.google.fr/books?id=9Hk_AAAAYAAJ&pg=PA65&lpg=PA65&dq=thailand+%22effective+precipitation%22&source=bl&ots=WK6JGZ29Y9&sig=2D9UuQzoMkXzAdKcFZoPyo_Bung&hl=en&sa=X&ved=0ahUKEwiUyMeStrTcAhUNbFAKHW2aCFk4FBDoAQgzMAI#v=onepage&q=%20effective&f=false
And the reference to Kung, 1971
You can consult the thesis of Dr. Pritam Mukherjee - all continuous data
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