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Reconstruction And Analysis Of Climate Change Based On Tree-ring Width Data In The Irtysh River Basin,xinjiang

Posted on:2016-08-26Degree:MasterType:Thesis
Country:ChinaCandidate:S X JiangFull Text:PDF
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The Irtysh River Basin is located in the southern slope of Altay Mountains. This area can be affected by westerly circulation, although it is far from the ocean. Because of the unique climate and topography, there are abundant primordial forests in the Irtysh River Basin. Seven sampling sites including 215 trees and 379 cores were situated at Altay and Fuhai and Fuyun forests. Only one site(KLD) was Larix sibirica,others were Picea obovata Ledeb. Using these tree cores, we developed seven standard tree-ring width chronologies. Based on the results of tree growth-climate responses, we reconstructed the historical climate in the Irtysh River Basin and analyzed its change characteristics. The main conclusions are listed as follows:(1) By analyzing the characteristics of tree-ring width chronologies in the Irtysh River Basin, we found all chronologies have many climatic signals. The changes of tree-ring width index of six spruce sites were similar, and their peaks and troughs were identical. The results show that it’s the same factor limiting the radical growth of spruce tree at the lower elevation of this region. We combined all the tree-ring width data from the six spruce sampling sites to develop a regional ring-width chronology(HEC). The higher mean sensitivity and standard deviation of HEC chronology indicate it has a greater climatic influence on tree growth. The higher expressed population signal show that tree-ring width of different trees varies identically. The confidence of the chronologies was evaluated by the subsample signal strength(SSS>0.85), and we obtained the reliable length of the HEC chronology spanning1722-2012(291 yr); the reliable length of the KLD chronology spanning 1579-2009(431 yr).(2) Based on the correlation between chronologies and local meteorological data,we found the precipitation of last July, August, December and current May, June in Fuyun weather station have good correlation with Picea obovata Ledeb tree-ringchronologies. The HEC chronology was significantly correlated with the precipitation from May to June(r=0.616, p<0.0001) and from previous July to current June(r=0.742, p<0.0001) of Fuyun weather station, but not significantly correlated with temperature change. The KLD chronology was significantly correlated with the average of mean June temperature of Altai and Fuyun station(r=0.658, p<0.0001), but not significantly correlated with precipitation change.(3) The precipitation from previous July to current June has been reconstructed back to A.D. 1722 for the Irtysh River Basin, using the regional tree-ring chronology from Picea obovata Ledeb. The precipitation reconstruction explained 54.2% of the instrumental precipitation variance during the period 1963-2012. The reconstructed precipitation series shows that 47 years are categorized as ‘wet years’, and 44 years are categorized as ‘dry years’. There are three wet events(1729-1731, 1803-1806,1913-1915) and two dry events(1810-1812, 1884-1886) existing in the precipitation reconstruction. Based on the 11-year moving average, the reconstruction series include nine wet periods and eight dry periods. The wettest period occurred during1984-2008 and the driest period occurred during 1877-1891. The period 1829-1876(48 yr) was the most extended wet period while the period 1807-1828(22 yr) was the most prolonged dry period.The precipitation reconstruction for the Irtysh River Basin existed the cycles 2.1a,3.2a exceeding the 95% confidence level and the cycles 2.3a, 21.6a, 24.3a exceeding the 90% confidence level. The reconstructed precipitation has an abrupt change from more to less occurring in 1876-1877 approximately and one abrupt change from less to more occurring in 1983 approximately. Spatial correlation analysis revealed that our precipitation reconstruction can represent not only the precipitation change in Altay Mountains well, but also the precipitation change in Tienshan Mountains to a degree.(4) According to the KLD chronology from Larix sibirica, we reconstructed themean June temperature from 1579 to 2009 for the Irtysh River Basin. The temperature reconstruction explained 42.0% of the instrumental precipitation variance during the period 1962-2012. The reconstructed temperature series shows that 68 years are categorized as ‘warm years’, and 67 years are categorized as ‘cold years’. Mean June temperature in 1955, 1957, 1904 were highest and in 1784, 1783, 1685 were lowest.Based on the 11-year moving average, the temperature reconstruction series include eight cold periods and eight warm periods. The coldest period occurred during1764-1801 and the warmest period occurred during 1608-1619. The period 1665-1711(47 yr) was the most extended cold period while the period 1862-1964(103 yr) was the most prolonged warm period.The temperature reconstruction existed the cycles 2.3a, 2.4a exceeding the 95%confidence level and the cycles 3.9a, 71.5a, 95.3a exceeding the 90% confidence level.The reconstructed temperature has two abrupt changes from high to low occurring in1767 and 1841 approximately. According to the results of spatial correlation analysis,it revealed that the temperature reconstruction can represent the early summer temperature change in Altay Mountains well. In addition, it can represent the early summer temperature change in northern Xinjiang, western Mongolia, southern Russia and parts of Kazakhstan.
Keywords/Search Tags:the Irtysh River Basin, Picea obovata Ledeb, Larix sibirica, tree-ring width, precipitation and temperature reconstruction
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