Study on causes and occurrence rules of seasonal drought in subtropical red soil hilly region

The causes and occurrence rules of seasonal drought in the subtropical red soil hilly region were systematically studied by analyzing the meteorological data．The results showy that the occurrence probability for“soil-plant”drought is 85．7％．among which that of moderate or severe drought is 50％ or so The highly frequent drought occurs in the period from July to August and from November to December each year．The drought occurring in July and August can cause a great damage to crops．The occurrence probability for climate-induced drought is 59.5％．among which that of moderate or severe drought is 31．0％.The“soil-plant”drought is more serious than the climate-induced one．The order of both the probabilities of these two kinds of drought and the extent of damage are 1990s> 1980s> 1970s> 1960s．indicating that it is decreasing for the ability of the red soil hilly region to resist the seaso nal drought，declining for the agro-ecosystem to resist the stress．