I am working on water balance in semi-arid regions of northern Ethiopia. The study catchment is about 550 square kilometer. In the study area, meteorological station was established before five years. I want you guys to suggest me the most possible ways (methods, models) to calculate the actual evapotransipiration of the area?
I thank you in advance!
Actual evapotranspiration of what surface cover? for that area you need for more than one weather station and use GIS to map ET of the area. I may need more clarification of the surface cover...
the last update was FAO 56 book ... for Kc values ... try to see there and depending of your crop ... I have worked with tomato and melon ... if it is one of them I can help ... http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf
Dear Elijah, many thanks for your answer. Regarding the surface cover of the study site, the escarpment has moderate vegetation cover in terms of trees and shrubs. However, the low-lying area (graben bottom) has sparse vegetation dominated by bare ground. At the outlet, the landscape has also a relatively good woody vegetation cover in the uncultivated plains and hills/ridges. Furthermore, there is crop cover during the rainy season (July to September). I hope you will forward your suggestion. .
@ Natasa, I thank you for your suggestion.
Dear Hailemariam Meaza,
A lot literature is available on net, but i find following article more useful for your study area.
Hossein Dehghani Sanija, Tahei Yamamotoa, Velu Rasiah,
Assessment of evapotranspiration estimation models for use in semi-arid environments. Agricultural Water Management.
Volume 64, Issue 2, 15 January 2004, Pages 91–106.
One way to tackle this is first to find out what vegetation (including bare ground surfaces) is present spatially and temporally. Then you can calculate the reference surface ET using either the FAO 56 or the ASCE Standardized method. And you could use the appropriate crop coefficients (either using FAO 56 or the locally developed one) to estimate the actual ET for that crop. You can then integrate all the actual crop ETs within the year to find out the actual crop ET in an annual basis.
Other option is to use the remote sensing method (SEBAL, METRIC, etc) to estimate the actual ET of that catchment, using the LANDSAT images.
Dear Elijah Phiri and Abhinaya Subedi,
Your suggestion is so helpful.
I thank you.
The best model to estimate crop evapotranspiration and water requirements is CROPWAT created and developed by FAO organization based on Penman-Montieth method. Also, you can use the remote sensing method if you can buy images for your study area.
Dear Hailemariam Meaza,
I came across another paper to estimate crop evapotranspiration using concept of Growing degree-days (heat units). Kindly download the following paper for details:
M.A. Salama, , Kh.M. Yousef, A.Z. Mostafa, 2015. Simple equation for estimating actual evapotranspiration using heat units for wheat in arid regions.
Journal of Radiation Research and Applied Sciences
Volume 8, Issue 3, July 2015, Pages 418–427.
Regards, Manik Kalubarme, BISAG, Gandhinagar, Gujarat State, India
Dear Manik,
The paper that you attached to me investigates ETa at different growing stage of wheat production area. Our area, semi arid region, smallholders cultivate mainly sorghum in the rainy season (end of June, July, August and beginning of September). Does applying this approach is robust to this site.
Again, I thank you for your scientific consultation.
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