青海省海西州德令哈地区近千年来年降水量变化特征分析

STATISTICAL CHARACTERISTICS OF ANNUAL PRECIPITATION VARIATION DURING THE PAST 1 000 YEARS IN DELINGHA, QINGHAI PROVINCE, CHINA

试图揭示位于我国青藏高原东北部的青海省海西州德令哈地区近千年来世纪尺度年降水量变化规律.分析结果表明,该地区近千年年降水量变化存在显著的多尺度周期变化特征,其中以13～18世纪中的200年主控周期最为明显,并在15～17世纪达到最强,而近200年则以准120年的周期振荡为主,且在19世纪两种主要周期变化趋势相反,在近百年又趋向一致.年降水量序列的均值突变一般以30～100年尺度最为明显,世纪尺度的均值突变时段分别为公元1100～1111年、1403～1449年及1615～1661年,表现为年降水量的减少,以及公元1321～1348年、1497～1557年、1728～1743年及1885～1891年,表现为年降水量的增加.200年以上时间尺度的方差突变主要表现为序列的低频变化幅度,从公元1220年前后至1580年前后持续增大,且以15世纪的方差突变最为明显.

Climate change has been an important issue in the present world. The annual or the seasonal precipitation changes are directly relative to agriculture, stock raising, and forest productions, and it has been a focal point in climate change and some relative research fields. In order to study the statistical characteristics of annual precipitation variation for the past 1 000 years in Delingha, Qinghai Province, Northwest China, the wavelet spectral analysis, the singular spectrum analysis and the scanning tests were applied for the reconstruction of time series from seven chronologies built by tree ring samples collected in mountains along northeastern margin of Qaidam Basin. The periodical signals in the precipitation series can be detected by the first two statistical methods mentioned above, and the last method is applied to figure out the abrupt change signals imprinting in the same series. The quasi-200-year cycle was present during the whole time period (A.D.1000～2001) of the series, especially in the period of A.D.1200～1800, being more intense during A.D. 1440～1640. From the end of the 18th century and the beginning of the 19th century to present, the dominant cycle changed gradually from quasi-200-year cycle to quasi-120-year cycle. The phases of these two dominant cycles are opposite in the 19th century, that the quasi-200-year cycle was in positive phase and the quasi-120-year cycle was in negative phase in the first half of the 19th century, and the phases are reverse in the second half of the same century. From the beginning of the 20 century, the phases of the two dominant cycles tended to become uniform, that the two phases are all in negative phase. The central time period (A.D.1920～1940) of this negative phase is in agreement with other studies on lower water time period of A.D.1922～1932 over the Yellow River basin. The reconstructed series by the first four empirical orthogonal functions, which represent the quasi-200-year cycle and the quasi-120-year cycle, from singular spectral analysis shows that it can imitate the lower frequencies (corresponding with the century scale) changes of the annual precipitation series quite well. The abrupt changes are also detected in the annual precipitation series, being more obvious with 30-120 years time scales, by the scanning t test, the scanning F test and the scanning Lepage test methods. The abrupt changes of decade-century scales on the average value are present in seven time segments, in which the annual precipitation increased in A.D.1100～1111, 1403～1449 and 1615～1661 and decreased in A.D.1321～1348, 1497～1557, 1728～1743 and 1885～1891 respectively. The abrupt changes of more than 200 years time scales on the variation amplitude shows that the amplitudes of lower frequencies changes increased during A.D.1220～1580, in which the changes are more significant in the 15th century. By comparison with other studies on the dryness/wetness or drought/flood conditions in China’s history, the abrupt changes on the average value are common, with wet climate trends, over Eastern and Western China in the first half of 16th century, the first half of 18th century and the end of 19th century. Our data suggest that the abrupt changes occurred at these three time segments corresponding with large spatial scales in China.