THE CHANGES OF PRESENT PRECIPITATION AND HISTORICAL DROUGHT FREQUENCY IN ARID AND SEMI-ARID REGIONS OF CHINA

In this paper, present precipitation and historical drought frequency in arid and semi-arid regions of China are analysed. It is found that in North China, east part of semi-arid regions of China, precipitation has decreased markedly since 1950s' and in I980s' it was lower markedly than normal. In the past of 520 years, historical drought frequency had striking 100-130 years quasi-period. The drought high fequency spells were 1480s, 1610s, 1720s, 1830s, 1930s, respectively. And the drought low frequency spells were 1560s, 1670s, 1770s, 1880s, respectively. The most of serious drought in history often occurred in drought high frequency spell. And in most of the drought high frequency spells in hstory, there were the most serious droughts.