关键词: 挥发油, 挥发油, 朱砂叶螨, 气质联用(GC-MS), 半数致死浓度, 川芎

Abstract: In order to study the precipitation characteristics and future trend in Xi’an, the data of different grades of precipitation and the days of precipitation in Xi’an from 1951 to 2013 were analyzed with linear regression, Mann- Kendall detection, R/S analysis and ARIMA model. The conclusions are as follows: (1) different grades of precipitation, including light rain，moderate rain，heavy rain and the above, and the total rain all showed a decreasing trend from 1951 to 2013, with a decreasing rate of - 7.3, - 2.6, - 3.0 and -13.6 mm/10 a respectively; except for moderate rain, different grades of precipitation and the total precipitation reduced suddenly in the late nineteen sixties to seventies; (2) the days of light rain and total rain showed a decreasing trend, with a decreasing rate of -3.3 and -3.6 d/10 a respectively, and reduced suddenly in the late nineteen eighties, especially reduced at 0.05 significant level after the late nineteen nineties; the days of heavy rain and the above appeared periodical increase and decrease; (3) in the future, the precipitation and the days of light rain, heavy rain and the above, and the total rain will continue to decrease; the persistent strength will perform as light rain＞the total rain＞heavy rain and the above, but the moderate rain will increase. Hurst Index experiment can be used to detect the moment of mutation or significant change. The relative prediction error of future annual precipitation and precipitation days by ARIMA model is less than 20%, so it can be used for the short-term precipitation prediction.