CHANGE CHARACTERISTICS OF SEVERE RAINFALL AND EXTREME RAINFALL IN FLOOD SEASON OVER YUNNAN-GUIZHOU PLATEAU IN RECENT 47YEARS

Using the daily rainfall data of 159stations during the flood season(from May to October)in the period of 1961～2007in Yunnan-Guizhou Plateau,the severe rainfall and the extreme rainfall thresholds of different stations was defined by percentile method,and the severe rainfall and the extreme rainfall events were analyzed.The results showed that in geographic distribution features,the thresholds of the severe rainfall and the extreme rainfall events in Yunnan-Guizhou Plateau had biggish difference.The correlation of the thresholds with the total precipitation in flood season was not significant,but with the sea level elevation of stations was close negative.The variation trend of the total precipitation in flood season was not obvious in the period of 1961～2007,but the rainfall days displayed a significant decreasing trend,and the precipitation had a concentrating trend.The severe precipitation and the extreme precipitation had similar annual undulation features with the total precipitation in flood season,and the correlation of the extreme precipitation with the total precipitation in flood season was better than the severe precipitation.Using the ratio of the severe rainfall and the extreme rainfall to the total rainfall in flood season indicated the intensity of events.Both of them showed remarkable rising,and occurred a sudden rising change in the beginning of 1990s.There was an obvious anticorrelation between the severe rainfall,the extreme rainfall and the change of summer monsoon intensity.