Takaya et al. - 1974 - Rice cultivation and its environmental conditions

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214 Y. TAKAYA, K. KYUMA, and K. KAWAGUCHI Fig. 2. A map of the Mediterranean region showing the six climatic regions. Downloaded by [37.24.145.98] at 13:58 25 May 2015 30 mm of rain on a long term average. But this is naturally not sufficient to balance with the potential evapotranspiration of the order of 100-120 mm/month in mid summer. Group II occurs in north central Spain and in the interior of southern Italy. Thetemperature regime is more continental, having a wider range of fluctuation. Monthlyrainfall is less than 50 mm for the most of the year. It is about 20 mm for the driest months, July and August. Group III occurs only in northern Italy. Reflecting the higher latitude, the lowest mean monthly temperature is as low as ooc in January. The rainfall pattern is specific, being least humid during the winter months. Monthly rainfall exceeds 60 mm for most of the months. Group IV is typically Mediterranean climate, very mild in winter and quite hot and dry in summer; It is widespread throughout the southern parts of the Iberian and Italian Peninsulas and such islands as Mallorca, Sardinia, and Sicily. The three summer months are very dry, having even less than 10 mm of rain per month, while the period from October through March is moderately humid. Group V occurs in east central Spain and along the Adriatic coast of Italy. It issimilar to Group II except that it has higher mean monthly temperatures throughout the year. Rainfalls are least during mid winter and mid summer, the scarcity of rain in the latter being more pronounced. Group VI stations· occur along west coast of Italy and in some isolated spots in Portugal. Monthly rainfall exceeds 50mm throughout the year, except the 40mm in July. A very conspicuous rainfall peak is seen in November, amounting to 160 mm. A water balance study by Thornthwaite's method revealed that climatic regions I, Ill, and VI are mostly humid (B), while regions II, IV, and V are subhumid to semiarid (C or D). Italy has no stations classified as semiarid or D, except in the island of Sardinia, while many stations in central and southern Spain are classified as D, and occasionally even as arid or E. The southern coast of Portugal is also classified as semiarid. In relation to rice cultivation, temperature condition seems to be adequate in the greater part of the region, although the rice growing areas are situated quite far north in latitude, between 37 and 45°. If we take l4°C as the lower threshold and if we secure 6 months for rice growing, Region ll is prohibitive and Region I is marginal. The Vouga valley in northern Portugal, for e;xample, belonging to Region J, used to have some rice acreage, but today no rice is cultivated because of the unfavorable
Rice Lands ·in Mediterranean Countries (1) 215 Downloaded by [37.24.145.98] at 13:58 25 May 2015 temperature condition. The remaining regions, III to VI, are suitable for rice cultivation during the period of May through October. In view of the fact that the summer season has only scanty rains in these regions and that rice requires a great amount of water for irrigation, the climate of the Mediterranean region cannot generally be regarded as favorable for rice cultivation. Only where the available-water-to-rice-landarea ratio is sufficiently high would rice become cultivable. In northern Italy, where extensive rice land is found, this condition is satisfied by the availability of water flowing down from alpine glaciers, in addition to the relatively abundant rainfall. In rice growing areas of Spain and Portugal, the condition is satisfied by limiting the rice land areas to the lowermost reaches of big rivers such as the Tejo and Sado in Portugal and the Guadalquivir and Ebro in Spain, or to coastal lowlands where a few minor rivers supply fresh water. In Valencia, Spain, for example, the supply of fresh water to rice land is obtained from the J ucar and Magro. Once this basic water condition is satisfied, however, solar radiation is abundant due to the high intensity and length of sunshine hours, thus favoring a high yield of rice. Table 3 compares the solar radiation at different places ( 7) for the rice growing Table 3. Monthly averages of daily total solar ~adiatlon at different places for the six summer months (May through Oct., calorles/cm 1 /day), Country Japan Portugal Spain Italy Australia Location Sapporo Osaka Coimbra Llsboa Badajo~ Almeria Milano Sydney 1 l Latitude (N) 43•03' 34"39' 40°12' 38007' 38°53' 36"50' 45"28' 33•52' (S) May 406 297 555 626 421 552 493 512 June 412 249 590 691 594 588 499 530 July 390 343 607 720 610 595 515 560 August 349 344 540 626 544 541 430 440 September 299 266 428 482 419 443 325 500 October 225 243 341 354 296 337 188 410 Sum 2081 1742 3061 3499 2884 3056 2450 2952 ,, For Sydney the figures are for October through March. The rice growing areaa of inland New South Wales ehould have higher solar radiation than that of Sydney. period of May through October. In Sydney, Australia, the period of October through March is considered. Solar radiation in the Iberian peninsula ls comparable to that in rice growing areas of Australla, which are known to produce the highest average yield in the world (cf., Table 1). The monthly figures at Milano, northern Italy, are much higher than those in Japan throughout the rice growing period, except October. In addition, low humidity during the dry summer months would also favor rice cultivation through the reduction of Insect and pest hazards.
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Takaya et al. - 1974 - Rice cultivation and its environmental conditions

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