Dear Jim,
That is exactly what I want to do!
Just to describe it once again in detail for the other
DSSAT-list-subscribers:
Here at ICARDA we have on-station data in (at least) daily resolution
for the last ~25 years.
Hence, we have a good understanding on seasonal rainfall distribution,
probability etc.
Now, for the purpose of modeling long-term SOM-dynamics, I wanted to use
historic data from our Syrian colleagues that where gathered nearby
starting 1940. These are (in part) only available as monthly averages,
or in the case of rainfall, as monthly totals.
So I _don't_ want to generate completely random data, which could be
done by a multiple number of software tools, but rather stick as much as
possible to these observations.
For maximum and minimum temperature, I decided that a simple
interpolation is sufficient (I can explain in more detail what I have
done, if there is interest), but for rainfall this of course cannot be
done.
I will now test WeatherMan and report on my success or failure.
MarkSim will be next.
Best regards,
Rolf
P.S. I have tried 'LarsWG', but I failed to sort out how and which of
the various *.st* files I have to manipulate.
> -----Original Message-----
> From: DSSAT - Crop Models and Applications
> [mailto:[log in to unmask]] On Behalf Of James Hansen
> Sent: Thursday, July 17, 2008 16:36
> To: [log in to unmask]
> Subject: Re: disaggregate monthly rainfall data
>
> Dear Sommer,
>
> The most appropriate approach depends on how you want to use the data.
> Do I understand correctly that you want to generate a time series of
> daily data that exactly match the series of monthly totals, but with
> statistical properties that are consistent with the period of daily
> observations? If so, we have developed a tool for that purpose,
> described in:
>
> Hansen, J.W. and Ines, A.V.M., 2005. Stochastic disaggregation of
> monthly rainfall data for crop simulation studies. Agric. For.
> Meteorol.
> 131:233 246.
>
> It uses the same stochastic weather generator that I developed for the
> WeatherMan software distributed in DSSAT 4.x (described in: Hansen,
> J.W.
> and Mavromatis, T., 2001. Correcting low frequency variability bias in
> stochastic weather generators. Agric. For. Meteorol. 109:297-310;
> Mavromatis, T. and Hansen, J.W., 2001. Interannual variability
> characteristics and simulated crop response of four stochastic weather
> generators. Agric. For. Meteorol. 109:283-296; and Hansen, J.W., 1999.
> Stochastic daily solar irradiance for biological modeling
applications.
> Agric. For. Meteorol. 94:53-63.). It uses the same parameter file
that
> WeatherMan produces and uses for its unconstrained weather generator.
> However, it is constrained to reproduce a time series of monthly
> targets.
>
> I have not yet implemented a user-friendly GUI version. For my own
> work, I found it easier to use a stripped-down command-line version.
I
> have a stand-alone command-line version of the parameter estimation
> tool
> (extracted from what I developed for WeatherMan), stand-alone weather
> disaggregation tools for DSSAT and APSIM weather file formats, and a
> version that also deals with dewpoint and wind speed to support
> variations of the Penman model of potential evapotranspiration (used
> for
> the SARRA-H crop models). If you are interested, let me know, and I
> can
> send files and instructions.
>
> Regards,
>
> Jim
>
>
> Sommer, Rolf (ICARDA) wrote:
> > Dear all,
> >
> >
> >
> > I have historic rainfall data (1940-1985) as monthly sums, which I
> would
> > like to disaggregate to obtain approximate daily data to use it for
> crop
> > modeling. I wonder if anybody of you ever has done this, if there is
> > standard procedure or (even better) software that could do that for
> me.
> >
> >
> >
> > Of course, I have more recent (approximately 30 years) daily records
> of
> > the same region. So I could do all kind of supporting statistical
> > analyses.
> >
> >
> >
> > Best regards,
> >
> > Rolf
> >
> >
> >
> >
> >
> > ==============================================
> >
> > Dr. Rolf Sommer
> >
> > Agro-Ecosystem Modeling
> >
> > International Center for Agricultural Research
> >
> > in the Dry Areas (ICARDA)
> >
> > P.O. Box 5466, Aleppo, Syria
> >
> > Tel 00963 21 2691 590
> >
> > P Help save paper - do you really need to print this email?
> >
> > ==============================================
> >
> >
> >
>
>
> --
> James W. Hansen, Ph.D.
> Research Scientist - Agricultural Systems
> The International Research Institute for Climate and Society
> The Earth Institute
> Columbia University, Lamont Campus
> 61 Route 9W, Monell Building
> Palisades, NY 10964-8000
> USA
>
> voice: +1-845-680-4410
> fax: +1-845-680-4864
> e-mail: [log in to unmask]
> WWW: http://iri.columbia.edu/cgi-bin/staff?jhansen
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