Discussion of Precipitation Information in Xiagansate Tree-ring Chronology and 326 Year Precipitation Reconstruction
夏干萨特树轮年表中降水信息的探讨与326年降水重建

Xiagansate is located in the lower tree line of the mountainous area of the Urumqi River in the middle of Tianshan Mountain. Tree ring samples of spruce ( Picca schrenkinna var. tianschanica ) was collected from the lower forest zone. The ring width chronology of Xiagansate shows high mean sensitivity and high standard deviation which implied that it may contain much information of precipitation in such a semiarid region. The relationship between tree ring chronology and climatic factors was studied by correlation analysis. The ring width chronology shows the best relationship with the precipitation of May. Further study shows that the precipitation of the last ten day of May has the best relationship with the chronology. The result has distinct physiological significance. The radial growth of spruce was mainly occurred from May to August, and half of the ring width may be formed from May to June. The last ten day of May is the key period of radial growth and also the most active period. The precipitation of the last ten day of May has high deviation also correspond with the high mean sensitivity of the ring width chronology, which indicates the propriety of the relationship. The 326 years' precipitation of the last ten day of May was reconstructed from the ring width chronology and the low frequency variations of the reconstructed series was analyzed. There were 8 fully dry wet periods in the past 326 years, the driest period occurred from 1701 to 1722 and the wettest period occurred from 1961 to 1981. The frequency study shows that the reconstructed series has 64a, 32a, 22a, 14a, 5a and 11a cycles, some of which have relations with the solar activity such as the 11a sunspot cycle and the 22a Hale cycle. The method of variation analysis was used to predict the dry wet conditions of future years. The prediction will be very helpful for the yield predict and the planning of cropping system of winter wheat in North Xinjiang.