基于GPD分布的黑河流域极端降水频率特征分析

采用广义帕雷托分布(GPD)对黑河流域极端降水的频率特征进行了分析。采用百分位数法、Hill图法、年交叉率法选取了极端降水阈值,借助L矩法对GPD分布的参数进行了估计;采用Mann-Kendall和Pettitt方法对超阈值日极端降水序列的平稳性进行了检验。结果表明：① 采用百分位数法和Hill图法得到的日极端降水阈值差别很大,在综合考虑以上两种方法的基础上,结合年交叉率法,最终确定了流域各站点日极端降水的阈值;② 根据Mann-Kendall和Pettitt方法,超阈值日极端降水序列基本满足平稳性假定;通过Kolmogorov-Smirnov检验以及理论频率曲线和经验频率曲线的拟合程度可以看出,GPD分布能够很好地拟合研究区极端降水的分布特征;③ 通过分析理论累积频率达到90%以上的极端降水可以发现,黑河流域20世纪60年代发生极端降水的次数最多,其次是90年代以后,70年代、80年代发生极端降水次数较少;在过去51年间,下游发生极端降水的次数最多,其次是中游和上游。

Frequency analysis of extreme precipitation in Heihe River basin based on Generalized Pareto Distribution

With the great effects of global warming since the 20th century, extreme climatic events such as storm, drought, flood and heat wave occur more frequently in most regions of the world with longer duration and wider ranges of influence. Given the substantial economic and social consequences, the study of such events has become an important issue in climatic and the related sciences. Most basins in humid and semi-humid south and east of China were concerned for probability modeling analysis of precipitation extremes. While, for the inland river basins, there was a limited presence of such studies partly due to the limited data availability and a relatively low mean annual precipitation. The objective of this study was to carry out probability modeling of precipitation extremes in Heihe River basin, the second largest inland river basin in China, by using the peak over threshold (POT) method and Generalized Pareto Distribution (GPD), in which the selection of threshold and inherent assumptions for POT series were elaborated in details. Percentile method, Hill plot and the average annual occurrence number were used to select the threshold in GPD. L moment was used to estimate the shape and scale parameters. The inherent stationary assumption including no significant trend and no change point in POT series was verified by using Mann-Kendall test and Pettitt test. For comparison, another widely used probability distribution Gamma was employed as well. Results showed that, POT series derived from the aggregated methods were reasonable for the study area and approximately stationary based on the two tests. GPD could give satisfactory fits to the POT series for each station according to the Kolmogorov-Smirnov test, the theoretical and empirical cumulative probability curves and the return levels in different return periods. By investigating the theoretical cumulative frequency over 90%, it is found, in the 1960s, more extreme daily precipitation events were observed; in the 1970s and 1980s, the extreme daily precipitation events became less, while they became common in and after the 1990s. From the perspective of spatial scale, it happened more frequently in the lower reach than in the middle and upper reaches of the Heihe River basin according to the past 51 years (1960-2010) records.