黄土高原河龙区间最大日雨量(PMP)极值拟合及时空演变特征

黄土高原河龙区间暴雨可以造成极为严重的土壤侵蚀。为了探究河龙区间暴雨重现期的分布及变化规律,利用河龙区间及毗邻地区24个气象站点1957—2009年日降雨数据,分别用Gumbel分布和GEV分布模拟最大日雨量辨析这两种拟合方法的适用性,在此基础上,分析降雨极端事件的时空演变特征。结果表明:(1)对于短重现期(≤10a),两种分布模拟值最大日雨量(PMP)值相差较小;而在长重现期(≥20a)的水平上,GEV模拟精度较高。但若站点出现几次大暴雨且雨量相近的情况下,Gumbel模拟精度高于GEV模拟精度。(2)结合GEV分布和Gumbel分布,对河龙区间各站点的最大日雨量进行模拟。河龙区间2a,5a,10a,20a,50a,100a重现期的PMP分别介于40～70,50～85,60～100,70～110,85～130,95～150mm。河龙区间各重现期的最大日雨量的高值中心均分布在南部延河流域和西北部窟野河流域,而低值中心在西部横山以西和东北部偏关河以北地区。用3个时段数据(1950s—1960s,1970s—1980s,1990s—2000s)估算的5个代表站的最大日雨量值差异明显,在太原、榆林两站,1950s—1960s估算的最大日雨量较大,最大日雨量呈减少趋势。而在其它3个站点,均为1970s—1980s估算的最大日雨量较大。

Fitting of the PMP Values and Identifying Its Spatiotemporal Characteristics in the Helong Section on the Loess Plateau

There is high frequency of the heavy precipitation events in the Helong Section on the Loess Plateau.And the heavy precipitation events can cause severe soil erosion.The paper deals with the estimation of the return period of precipitation extremes in the Helong Section on the Loess Plateau.In this study,the daily precipitation datasets at 24 meterological stations from 1957—2009 were used to estimate the probable maximum precipitation(PMP) in the Helong Section.Two extreme distribution models of probability estimations were compared to identify the applicability: the GEV distribution and the Gumbel distribution.The spatiotemporal characteristics for the extreme events were detected.The results showed that:(1) for the return period less than 10 years,there was little difference between the two distributions for estimation of the PMP.But for the return period greater than 20 a,the GEV distribution was properly more than the Gumbel distribution to estimate the PMP in the Helong Section.When there were several heavy precipitation events with the similar precipitation values,the Gumbel distribution is properly more than the GEV distribution;(2) the PMP values in the Helong Section for the return period of 2 a,5 a,10 a,20 a,50 a,100 a were between 40~70,50~85,60~100,70~110,85~130,95~150 mm,respectively.The PMP value for a given return period was higher in the Yanhe River in the south and in the Ordos Desert in the northwestern Helong Section.However,it was lower in the northeastern part.The PMP values estimated by the daily precipitation data of the three period of 1950s—1960s,1970s—1980s,1990s—2000s were varied.The PMP values estimated by the datasets of 1950s—1960s in the Taiyuan and Yulin stations were higher.However,at the Dongsheng,Xingxian and Yanan stations,the estimated PMP values were higher for the datasets of 1970s—1980s.