用树木年轮重建天山中部近350 a来的降水量

单相关普查表明，乌鲁木齐河谷树轮年表与上年7月至当年2月降水相关显著.西白杨沟及波尔钦沟两个树轮差值年表可较好地重建出天山中部近350 a来该时段的降水量，解释方差达62％.经用统计参数、独立降水资料、历史气候记载、冰川及其它资料多方面验证，表明近350 a的降水重建序列是可信的.降水特征分析指出：天山中部降水可划分出3个偏湿期(1671(?)一1692年，1716－1794年，1825－1866年)和3个偏干期(1693－1715年，1795－1824年，1867－1969年).其后两个偏湿期与乌鲁木齐河源1号冰川前的第二、第三道终碛垄相对应，经推算，相应年降水量比现今分别偏多约59 mm及30 mm.天山中部上年7月至当年2月的降水具有5、10、53～54、3.7及3.3 a的变化准周期，在1716－1969年间存在着明显的变干趋势，并在1831年发生过突变.重建降水序列对乌鲁木齐、昌吉州天山北坡一带的降水具有较好的代表性.

Reconstruction of Precipitation in the Recent 350 a from Tree－Rings in the Middle Tianshan Mountains

Correlation census shows that the correlation between the tree-ring chronologies from the ürümqi River Basin and precipitation from July to February is significant with the best single correlation coefficient of 0. 74 and a significance level of 0. 0001. From two tree-ring residual chronologies of the West White Poplar Gully and Boerqin Gully, precipitation in the middle Tianshan Mountains in recent 350 a can be reconstructed, with an explanation variance of 62%. Many verifications, according to statistical parameters, independent precipitation data, historical climate records, glacial and other data, have shown that the reconstructed precipitation sequence for the recent 350 a is reliable. Analyzing the precipitation features indicates: 1) There were three wet periods, 1671(7)－1692, 1716－1794 and 1825－1866, with the reconstructed precipitation above the long-term mean, and three arid periods, 1693－1715, 1795－1924 and 1867－1969, with the reconstructed precipitation below the long-term mean;2) Three were two wet periods, 1716～ 1794 and 1825－1866, when the second and the third glacial terminal moraines formed before the Glacier No. 1 at the headwaters of the ürümqi River. According to a computation, annual precipitation during the 10 years when precipitation was maximum in the period of 1716－ 1794 was 534.1 mm, 59 mm more than now, with a precipitation anomaly of ＋12.5%. This is consistent with the conclusion that precipitation in the strongest period in the Little Ice Age was above 50 mm more than now, which was drawn by Yao Tandong and Shi Yafeng who have calculated that from temperature. Annual precipitation of the maximum ten-years precipitation during 1825－ 1866 was 504. 6 mm, 30 mm more than now, with a precipitation anomaly of ＋6.3%; 3)During the 348 a, the reconstructed precipitation in the middle Tianshan Mountains from July to February appeared 18 wet years( accounting for 5.2 %), 8 dry years(2.3%), 58 partial wet years(16.6%), 94 partial dry years (27.0%) and 170 normal years (48.9%); 4)In the recent 350 a, 1714 was the most wet year, with a precipitation, 507. 2 mm, from July to February, 96. 9% more than now(the mean was 257.5 mm during 1961－1993). 1787 was the most dry year, with a precipitation of 158. 6 mm, 38. 4% less than; 5)The variation of reconstructed precipitation from July to February has quasi-periods of 5, 10, 53～54, 3.7 and 3.3 a; 6)There was a significant drying trend from 1716 to 1969; 7)The reconstructed precipitation had an abrupt change in 1831; 8)The series of reconstructed precipitation is well representational to that in the ürümqi and Changji Prefectures on the north slopes of the Tianshan Mountains.