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概要：
98 高知論叢　第97号Productive variability and ENSO sensitivity are summarized in Table 6. Asexpected, the more ENSO sensitive, the more variable the production. Exceptionsare root crops (cassava and s....

98 高知論叢　第97号Productive variability and ENSO sensitivity are summarized in Table 6. Asexpected, the more ENSO sensitive, the more variable the production. Exceptionsare root crops (cassava and sweet potato) and groundnut. These crops are moderatelyvariable in production but ENSO non-sensitive. The common characteristics of thesecrops are drought tolerance, especially root crops, and they are widely grown undersub-optimal land and climatic conditions with traditional technologies (Horton, 1988;Wallis and Byth (eds.), 1987). Cassava, known as famine reserve, is cultivated in asubstantially wide range of agro-ecological settings at an altitude of sea level to 2,000masl and under annual rainfall of 500 mm to tropical rainforest. It can withstand5-month dry periods (Horton, 1988). Thus, production variability of these crops is moreattributed by the latter characteristic rather than the ENSO impact. However, it shouldalso be noted that their production is not fully represented in the official statistics sincethey are mainly grown as a second or third crop in a mixed cropping system for homeconsumption.Table 6. Productive variability and ENSO sensitivity by crop in the regionENSO sensitivityNone Weak Moderate StrongProductionvariabilityLarge MaizeModerateCassavaSweet potatoGroundnutSoybeanSmall RiceCompiled from Table 2.4 and 2.5.5. Summary and ConclusionsThe El Nino event has been increasingly frequent in the last 40 years. Comparedto production loss in non-El Nino years, that in El Nino years was characterized by: i)Absolute magnitude (El Nino years: 7 per cent vs. non-El Nino years: 3 per cent); ii)Simultaneity of both yield and area decline (production loss in non-El Nino years wasmainly caused by yield decline); and iii) Single year phenomenon with recovery ofproduction in the following year.Among the six major food crops, maize was most sensitive to ENSO for both