There are different temperature based estimation methods. Hargreaves (HG), Thornthwaite (TW), Blaney- Criddle (BC) and Linacre (Lin) are some of them. FAO Penman Monteith needs more parameters but it seems more accurate.

Choosing which methods related to climate and region.

If emprical methods modify with local coefficient such as HG or TW, they can be more useful and accurate with less data requirement.

Each method has it's benefits as well as tradeoffs that you have to weight into in line with your experience, resources, timeline, etc. Thus, as much as I would recommend the Penmon Moneith method, it too has its own problems. i suggest that you review the literature on each of those methods as well as others that may be available out there and make an informed decision. I always use the Penmon Moneith method to calculate potential EP, but instead of using or relying on averages of climatic data/parameters, i used an evaporation pan or install a climate station to gather the necessary datasets, a reference crop to estimate the crop/plant coefficient, etc and those I can generate I contact the nearest climate station. It is neither a bad idea gathering all those data (multi-year) from a climate station nearest to your research area. Check my profile for some materials.

Alternatively, here are few very useful resources to calculate ETc

http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf  or source it from: https://www.researchgate.net/publication/

http://edis.ifas.ufl.edu/pdffiles/ae/ae45900.pdf 

http://www.civil.utah.edu/~mizukami/coursework/cveen7920/ETMeasurement.pdf

Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating reference evapotranspiration (ET0). Still there are different approaches (requiring less data) which estimate ET0 closely to Penman-Monteith method for different climatological conditions, I think that HG method is more accurate.

Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating reference evapotranspiration (ET0). Still there are different approaches (requiring less data) which estimate ET0 closely to Penman-Monteith method for different climatological conditions, I think that HG method is more accurate.

It’s dependent on your purpose and also sort of data that it is available for you.

Thank you for your answers Sir Actually I want calculate the PET (potential evapo-transpiration) for the hot semi-arid region then can u suggest me which method  should be used to have better results

The answer to your question is simple: The best method for PET (ETo) calculation is Penman-Monteith method. Nowadays this method is used as a standard for the Evapotranspiration calculations. It is tested in different climates and show best results comparing to other methods. The main weakness (for wider use) of this method is high climate data requirements (temperature, wind, humidity and solar radiation), that is why FAO developed: ETo limited (ETo lim), wich is based on PM equation but for calculation of PET (ETo) require less data. 

You can use FAO software: ETcalc (in attachment).

All the best!

http://www.fao.org/nr/water/eto.html

http://www.bioone.org/doi/pdf/10.1659/MRD-JOURNAL-D-14-0024.1

http://www.tandfonline.com/doi/pdf/10.4296/cwrj1301009

I also recommend the Penman-Monteith Method.

Hi Shruti

Certainly, Penman-Monteith FAO56 is a standard method that FAO has recommended it for calculate reference crop evapotranspiration.

Book Crop evapotranspiration-Guidelines for computing crop water ...

But if you haven't wind speed and relative humidity, you have to use temperature or radiation based methods that are dependent on your data and your target.

I recommend, like others, the method proposed in FAO56. If the weather station you use is not in reference, then you will get potential evapotranspiration. If you have limitations in the meteorological variables, you can use other methods such as Hargreaves -Samani or Priestley-Taylor, recomended by FAO56.

If you need to make evapotranspiration maps, there are simple methods (statistics) that deliver good results. Please see the example that I sent you in this way: dx.doi.org/10.1080/01431161.2017.1323287 (Monthly calibration of Hargreaves–Samani equation using remote sensing and topoclimatology in central-southern Chile)

Hello,

I think the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating reference evapotranspiration (ET0)...

Regards,

Dear all

the FAO+56 IS THE BEST AND ACCURATE FORMULA FOR CALCULATING THE ET0.

BEST REGARDS

Potential evapotranspiration (ETP), expressed as the evaporated water slice, is the sum of the amounts of water that can evaporate and transpire on a given surface and for a well-defined period of time, considering inputs from sufficient water. For the estimation of potential evapotranspiration, you can used the Thornthwaite formula which established a correction between monthly mean temperature and monthly evapotranspiration.

If you have a lot of meteorological data, I recommend for calculated PET or ETo use Penman-Monteith method. But if you have limitations with meteorological data, it is possible to use Hargreaves-Samani method. In both cases, I recommend calibrating these methods for your study area.

I suggest, like others researchers, the method proposed in FAO56.

NCL: NCAR Command Language

Many 'crop' examples are at:

http://www.ncl.ucar.edu/Applications/crop.shtml

Crop Functions .. including FAO56 examples

http://www.ncl.ucar.edu/Document/Functions/crop.shtml

If you have only temperature data, check Penman-Monteith temperature (PMT) equation, that is the version of Penman-Monteith estimating missing data. This approach showed good performance among temperature based equations in the studies below.

J. Almorox, A. Senatore, V.H. Quej, G.Mendicino Worldwide assessment of the Penman-Monteith temperature approach for the estimation of monthly reference evapotranspiration

Theor. Appl. Climatol., 131 (2018), pp. 693-703, 10.1007/s00704-016-1996-2

L.B. Ferreira, F.F. da Cunha, R.A. de Oliveira, E.I. Fernandes Filho Estimation of reference evapotranspiration in Brazil with limited meteorological data using ANN and SVM–a new approach

J. Hydrol. (2019), 10.1016/j.jhydrol.2019.03.028

For daily data prefer PM (FAO56), for monthly data use TM.

FAO 56 is the best and universally accepted

Hello Dr Shruti Bansode

The evapotranspiration is a fundamental variable in the hydrological cycle and is a key factor for water balance and irrigation.

The penman monteith method is more accurate than the Thornthwaite method because it takes into account several climatic parameters including air temperature, relative humidity, wind velocity, sunshine duration, etc.

See the attached file for more details on the penman monteith method

Best regards

Fatah BOUTELDJAOUI