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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