Time trends and variations in mean and accumulated solar radiation for the ripening period of paddy rice in kyushu for 1979-2007

Abstract

A notable declining trend in the eating quality of rice panicles has been observed in Kyushu, Western Japan, since the 1990's. As solar radiation is one of the factors determining eating quality, this study investigated the recent time trends and variations in the mean and accumulated radiation for the ripening period of paddy rice in Kyushu during the period 1979-2007. The 3-year running mean radiation data, which are dynamically downscaled reanalysis data using the non-hydrostatic regional climate model (NHRCM) with a grid interval of 20 km, were used for analysis after the validation. From a meta-analysis of governmental crop statistics, it was found that the ripening period (i.e., the period between heading and harvesting) in Kyushu was shortened by 10 days in a 29-year period and generally occurred between the end of August and early October in the 2000's but between early September and the end of October in the 1980's. The change in the length and timing of the ripening period resulted in decreased accumulated radiation for the period, although the mean radiation during the period increased as a result of the earlier timing of the ripening period. The empirical orthogonal function (EOF) analysis results showed that the earlier timing and shorter ripening period are the most dominant factors explaining the radiation change during the ripening period in Kyushu in the past three decades. In addition, a more westward extension in Pacific anticyclones and an associated change in the locations of precipitation that decreased the mean and accumulated radiation for the ripening period in the area were frequently observed in the 2000's. These results indicate a more adverse radiation condition for paddy rice production in the 2000's compared to the 1980's and 1990's. © 2012, The Society of Agricultural Meteorology of Japan. All rights reserved.