Effects of Monsoonal Fluctuations on Grains in China. Part II: Crop Water Requirements

Abstract

This paper continues the description of the effects of monsoonal variability in regard to crop evapotranspiration (ET) and irrigation needs of rice, maize, and wheat for 16 Chinese stations between 1961 and 1975. For this analysis the previously introduced YIELD model was applied. Two measures of drought were used to examine year-to-year changes: a drought index based on monthly precipitation totals and a relative ET deficit defined as the ratio of actual to potential ET as determined from the model. The correlation between the two drought measures are −0.585, −0.783, and −0.704 for rice, maize and wheat, respectively. Differences can be explained by meteorological conditions for specific years and varying plant responses to drought. The two approaches often identified different dry and wet years. The study determined the probable yearly changes of ET and irrigation on a regional and specific-station basis. Drought episodes were found to be crop-specific. For instance, 1965, 1968, 1972 and 1975 were drought years for maize and wheat, whereas 1963, 1968 and 1969 were drought years for rice. The use of mean meteorological data for a time period, in place of actual year-to-year data, can create considerable errors, varying with crop type and region. According to the annual ET deficit, Peking showed the greatest range for maize and wheat for the 15-yr period. This range was highest for rice at Chengtu (Szechwan) and Nanking (Anhwei). Generally, year-to-year irrigation changes mimicked the ET patterns.