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Date: | Tue, 7 May 2002 16:52:14 -0400 |
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Dear Roger,
This is easy to do at the country scale using the FAOSTAT online data
base (http://apps.fao.org/). With Colleagues at Goddard Institute of
Space Studies, I looked at FAOSTAT maize time series data, using a
spectral smoothing filter to identify trends, for most countries. Our
purpose was to characterize influence of the El Nino-Southern
Oscillation, requiring us to account for any long-term trends. The
upward trend is pretty consistent. We did not publish the analyses. I
have also seen presentations of positive trends for rice from several
tropical Asian countries. While I don't think a positive trend is
universial in the tropics, it seems pretty common for the major field
crops. You are right about the difficulty of attributing a positive
trend to any one causitive factor. However, crop simulation should be
able to isolate climate-induced trends (positive or negative).
I hope this helps.
Roger Rivero wrote:
> Dear friends:
>
> In published literature about yield forecasting in middle
> (temperate) latitudes it has become a tradition (so it seems to me)
> to decompose yields time series in a linear or nonlinear mean
> trend plus a random perturbation that alternates in sign about this
> mean trend.
>
> The mean trend is almost always an upward one and have been related
> to the steady progress in technology (cultivars, management, etc.)
> while the random perturbation have usually been assigned to climate
> variability. This random component have been the subject of
> forecasts methods based in statistics, longe range weather
> forecasting, biophysical models or whatever.
>
> Though I donīt have enough data to make any assertion about it, I
> would like to know if any of you have been able to documentate such
> an upward trend in (actual) yields for low (tropical) latitudes.
>
> It seems to me that a trend in yield could be not only the result of
> technological development but of other factors as climate change.
> But what could be worse, an upward trend may not be present in
> lower latitudes because of a negative impact of climate change and
> unsustainable land management leading to progressive degradation of
> agricultural ecosystems in spite of technological improvements as
> irrigation, more productive cultivars and fertilizers.
>
> I would like to know if some of you have been able to documentate
> these trends in lower (tropical) latitudes.
>
> Roger E. Rivero Vega
>
Regards,
--
Dr. James W. Hansen
Associate Research Scientist - Agricultural Systems
International Research Institute for Climate Prediction
P.O. Box 1000
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/ForOne.cgi?jhansen
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