Dear all,

While it is true that a number of assumptions are made in order to use
the FAO Penman-Monteith equation with limited data sets, it has been
proven that still the differences in results between using Penman-
Monteith with full data as opposed to limited data sets are however
smaller than the differences when using any alternative ETo equation,
including Priestley-Taylor.

You can find further details on this topic at:

http://www.fao.org/docrep/X0490E/x0490e06.htm#need%20for%20a%20standard%20eto%20method

Regards,

Giovanni Munoz
FAO


On 28 Apr 2011, at 21:02, Boote,Kenneth J wrote:

> All,
>
> I don't think Jon is right on this.  I think that if you specify the
> FAO-56 ET option and only have SRAD, Tmin, Tmax, and rainfall, the
> model will still run FAO-56, but it does this with the assumption
> that Tdew is equal to Tmin, and with a default windspeed that is
> buried in the code somewhere.
>
> Jon is right in saying that you should really only use Priestley-
> Taylor in this case.  But I think the model runs FAO-56 with the two
> assumptions that I indicated.
>
> Happy computing,
> Ken Boote
>
> -----Original Message-----
> From: DSSAT - Crop Models and Applications [mailto:[log in to unmask]
> ] On Behalf Of Jon I. Lizaso
> Sent: Thursday, April 28, 2011 11:40 AM
> To: [log in to unmask]
> Subject: Re: Evapotranspiration Model
>
> Kelsey,
> If only the minimum weather data set is available, then the model
> will use
> the Priestley-Taylor method. To use Penman-Monteith-FAO56 method you
> will
> need information on wind and dew-point temperature.
> Best regards,
> Jon
>
> -----Mensaje original-----
> De: DSSAT - Crop Models and Applications [mailto:[log in to unmask]
> ] En
> nombre de Brandt, Kelsey
> Enviado el: Thursday, April 28, 2011 4:13 PM
> Para: [log in to unmask]
> Asunto: Evapotranspiration Model
>
> Hi all,
>
>
>
> If we only have a minimum data set (SRAD, Minimum Temperature, Maximum
> Temperature and Precipitation), and select FAO56 as our
> evapotranspiration
> model, what model is actually used?  Does DSSAT default to a certain
> model,
> or will it calculate values so it can use the FAO56 model?
>
>
>
> Thanks,
>
> Kelsey
>
>
>
> Kelsey Brandt
> Semiarid Prairie Agricultural Research Centre | Centre de resecherches
> agricoles de la region semi-aride
> Agriculture and Agri-Food Canada | Agriculture et Agroalimentaire
> Canada
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