Application of a progressive-difference method to identify climatic factors causing variation in the rice yield in the Yangtze Delta, China

Time series of rice yields consist of a technology-driven trend and variati ons caused by climate fluctuations. To explore the relationship between yie lds and climate, the trend and temporal variation often have to be separate d. In this study, a progressive-difference method was applied to eliminate the trend in time series. By differentiating yields and climatic factors in 2 successive years, the relationship between variations in yield and clima tic factors was determined with multiple-regression analysis. The number of hours of sunshine, the temperature and the precipitation were each defined for different intervals during the growing season and used as different re gression variables. Rice yields and climate data for the Yangtze Delta of C hina from 1961 to 1990 were used as a case study. The number of hours of su nshine during the tillering stage and the heading to milk stage particularl y affected the yield. In both periods radiation was low. In the first perio d, the vegetative organs of the rice crop were formed while in the second p eriod solar radiation was important for grain filling. The average temperat ure during the tillering to jointing stage reached its maximum, which affec ted rice yields negatively. Precipitation was generally low during the join ting and booting stages, which had a positive correlation with yield, while high precipitation had a negative effect during the milk stage. The result s indicate that the climatic factors should be expressed as 20- to 30-day a verages in the Yangtze Delta; a shorter or longer period, e.g. 10 or 40 day s, is less appropriate.