Simulated analysis for 110 years of seasonal weather impacts on Yangtze Delta rice harvest yields

Abstract

The Yangtze Delta (30°N–32°N, 120°E–122°E) is one of the important high yielding rice growing regions in China. The paddy fields there are chiefly rainfed and therefore the impact of weather on rice yield is very marked and causes violent fluctuations in the annual output. However, the available sequence of annual rice yield data is too short to be used to analyse and predict the annual yields from associated seasonal weather impacts. Therefore, a longer sequence of rice yield data has long been hoped for, and has now been worked out by the authors through simulated analysis techniques. The available rice yield data of the years 1951–1980 are processed and used as an annual harvest sequence with reference to the weather factors of rainfall from June to September and the temperature in July. Again, by using the classification method AID (automatic interaction detection), a statistical model is established to simulate a long sequence of annual harvests for the past 110 years from 1873 through 1982. Based on the simulated result, an analysis of the frequency of the rice harvest fluctuation in the Yangtze Delta shows that, on average, good and bumper harvests amount to some 45%, bad and disastrous years 25%, and normal years 30%. However, the distribution of the frequency is not homogeneous and the phases of better and worse harvest alternate, the length of one period of long-term fluctuation being ∼36 years. Also, the Circulation-Weather-Harvest system (CWH) is discussed with regard to both long and short terms.