新疆洪灾时间序列突变及其气候原因分析

Abrupt Change in the Time Sequences of Flood Disastersin Xinjiang and Its Possible Climatic Reasons

利用统计方法对新疆农田洪灾成灾面积和洪灾次数时间序列进行了非参数突变检验,发现新疆农田洪灾成灾面积和洪灾次数时间序列在1980年代中后期发生了明显的突变.突变现象在洪灾直接经济损失上也有明显表现,主要表现为洪灾直接经济损失在1980年代中后期出现了明显的差异,即1980年代中后期以前损失较低,之后急剧增大.在分析了洪灾序列和降水序列的相关关系的基础上,认为1980年代中后期新疆洪灾损失突变的主要原因之一是此时期新疆气候发生了由干到湿的转折.

Based on the flood damaged area, the annual number of the flood-disasters, and the value of financial loss in historical documents from 1950 to 2001, it is found that there is an increasing tendency in flood disasters in Xinjiang in recent 50 years, especially after the 1980s. A non-parameter test (Mann-Kendall test) is employed to survey the abrupt change year for the time series of flooded index, which is derived from the flood-affected area divided by the cultivated land, from 1950 to 2001 and the time series of annual number of flood disasters from 1950 to 1993 in Xinjiang. The years 1986/1987 and 1988 are hence checked out as the abrupt change points with the confidence interval of 95% for the two time series, respectively. Examining the yearly frequency and damages caused by floods indicates a relative increase in loss since the 1980s. It is found that there are three periods when the direct economic loss due to numerous flood catastrophes was different, i.e., a high damaged period from the mid-1980s to the 1990s, a low damaged period from the early 1960s to the early 1980s, and a medium damaged period in 1950s. The reason of abnormal change of the flood disasters in Xinjiang is discussed from viewpoint of climate variability, by correlating the time series of flood-damaged area to the annual precipitation. The analysis shows that there is a linear correlation between the series of the flood damaged area and precipitation in Xinjiang during 1961-1998, with a correlation coefficient of 0.608. The correlation, however, is relatively low with a correlation coefficient of 0.196 for the period 1961-1986 and becomes much close during the period 1987-1998, with a correlation coefficient of 0.68. Evidence shows that the number of heavy rainfall, together with the frequency of floods, has increased in Xinjiang since the 1980s. Therefore, the abrupt increase in flood disasters can be attributed mainly to the increase of precipitation in Xinjiang since the mid 1980s.