参考作物蒸腾量的多重分形特性分析

Multifractal Analysis of Time Series of Reference Crop Evapotranspiration7

分析ET(Evapotranspiration,参考作物蒸腾量)的动力学特性,有助于进行中长期需水量的分析与预测。将多重分形特性分析方法应用于1978—2007年间30 a汉江流域3个典型站点(钟祥、天门、武汉)的参考作物ET时间序列。结果表明,逐日参考作物ET序列不仅具有不规则的高频振荡的特征,而且还具有明显的分形行为;在不同时间宽度(日、旬、月)下,逐日参考作物ET序列的多重分形特征最强。进一步的分析结果表明,序列中脉动引起的波动相关性和极端事件引起的胖尾概率等都是引起多重分形特征形成的原因。结合趋势转折分析方法发现:不同时间阶段内的多重分形特征显著;但在不同的时间段内,多重分形谱和局部分维宽度等都受到了极端事件的影响,且影响幅度与所处流域内的位置有关。

In order to predict water requirement in the medium-to-long period,we studied dynamics features of reference crop evapotranspiration. Multifractal analysis was applied to the time series of reference crop evapotranspiration of three stations（ Zhongxiang,Tianmen and Wuhan）,located in Hanjiang basin from 1978 to 2007. Results show that,the daily reference crop evapotranspiration contains characteristics of irregular high-frequency fluctuation and exhibits the strongest multifractal characteristics among different time intervals such as one day,ten days and one month. Further analysis by partition function shows that,most part of multifractality in the time series＇ data was due to correlations caused by fluctuations and the fat-tailed probability distributions caused by extreme events. Moreover,the multifractal features vary within the different parts of the time series and the changes can be explained by the methods of piecewise linear fitting and trend changing points（ PLFIM）. Finally,both of multifractal spetrum and local piecewise width are influenced by extreme climate events in different time intervals,and the effects of extreme climate events are relevant to different locations in basin.