Vergara - 1976 - Physiological and morphological adaptability of ri

CIEOGRAPHY‘ AND (ILIh-LATE or RICE 47
"Before 1920. stations in northwestern India experienced years with less than half of normal
rainfall with a probability of 0.116 or a “return period“ of around 8.6 years. From I920
through 1960 the probability of such a dry year was 0.07] for a return period of about l4
years. During the 1930's, the wamiest decade of this century in temis of mean temperature
in the Nonhem Hemisphere. the probability was 0.055 or about once in l8 years. If the
climate returns to that typical of the period before 1920. will a half-again-as-prohable recurrence
of drought be significant in that hungry land?“
Metcorologists such as Brfrson (1974) and Mitchell ( 1971] are not in complete
agreement as to the causes of the temperature decreases which appear ultimately
responsible for our current changes in climate. A very strong case is made by
Bryson for man himhelf as a major contributor to the cooling effect. He points
out that aerosols produced by industry‘. by mechanized agriculture, by overgrazing.
and by the burning of swiddcn fields have all contributed to the dust
blanket which by the mid-l950“s had overpowered the warming effect of an
added CO, load. Mitchell on the other hand argues with conviction that the
eflectofinananade aerosoh is anflnguous and thatthe coohng is pan of a
long-term natural cycle.
To the rice farmer and rice scientist the causes are of less immediacy than the
facts: first, that droughts are recurring with increasing frequency and second,
that temperatures are gradually decreasing. The impact will be greatest on the
rainfed paddy in transitional climate zones.
The problem of great urgency is to develop rice varieties able to withstand
drought and able to produce reasonable yields under conditions even more
difficult than those prevailing today. I would urge the rice scientists assembled
here to redouble their efforts. Perhaps even now it is not too late.
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