近50年延安市汛期极端降水事件变化研究

Analysis on the Extreme Precipitation Events in the Flood Season of Yan'an City for Nearly 50 Years

利用1961～2010年延安市的降水日值资料,对延安市的汛期极端降水事件变化进行统计分析。结果表明,延安市汛期(5～9月)降水量对当地年降水起决定性作用。延安市汛期极端强降水日阈值为32.6 mm,极端强降水量以10.65 mm/10a的趋势下降;延安汛期相对阈值(R95p和R90p)表现出相近的变化,呈弱减小趋势;绝对阈值(R25mm和R50mm)两者的变化与R95p和R90p相近。进入21世纪后,汛期降水量有所回升,极端强降水量、极端降水强度呈弱增加趋势,但极端降水日数、暴雨日数趋于减少,表明在气候变暖的背景下,延安市汛期降水越来越集中,旱涝灾害有增加趋势。

According to the daily precipitation data in Yan＇ an City from 1961 to 2010, the changes of extreme precipitation events during the flood season were analyzed. As indicated by the results, the rainfall amount during the flood season from May to September in Yan＇ an plays a decisive role in the precipitation of the whole year. The daily threshold value of extreme strong rainfall was 32.6 mm,and the extreme strong rainfall amount declined at a rate of 10.65 mm/10a. The relative threshold （R95p and R90p） showed a similar change, presenting a declining tendency. While the absolute thresholds （R25 mm and RS0 mm） kept in the similar step with the change of R95p and RgOp. In the 21st century,the flood season rainfall increased,the extreme strong rainfall and extreme precipitation intensity tended to increase with a low speed. However, the extreme precipitation days and heavy rain days tended to reduce,indicating that the rainfall of Yan＇ an city is more concentrated and there is a trend of increase in droughts and floods disasters.