The Impact of the Tibetan Plateau on the Climate and Double Cropping of Rice at Some Localities in the Northern Subtropics of China

抄録

The extension of double cropping of rice in the Northern Subtropics of China since the 50's and 60's has yielded significant promotion of grain production at most localities for many years. However, this change in the cropping system also brought about some troubles: the early rice suffered more frequent spring cold and the late rice suffered more frequent autumn cold, etc. The influence of the Tibetan Plateau is considered to be essential to the occurrence of cold air outbreaks in East and Southeast China in spring and autumn as well as in winter. When the jet stream displaces southward from its normal position, it is divided into two branches by the Tibetan Plateau. There appears a trough in the southern branch located in the Bay of Bengal. There is another trough generated due to the dynamic effects of the Tibetan Plateau in the northern branch of jet, and this trough is located east of the eastern boundary of the Plateau. These two troughs are out of phase, and they induce warm and wet air advection in the upper air layer and cold air advection in the lower air layer. Hence long spells of cold and rainy weather appear in the Middle and Lower Reaches of the Yangtze River both in spring and autumn and will do harm to early and late rice.
Comparative studies of spring and autumn cold, between eastern and western parts of the Northern Subtropics of China and their influences on the yields of early and late rice are made.