Temperature Change Recorded by Tree Ring in Jiuquan during the Period from June to September in Recent 240 Years

Some tree-ring samples were collected with increment borers(5 mm and 15 mm) from 4 sites to study the historical temperature variation in the Qilian Mountains,China.Six different tree-ring parameters(earlywood width,latewood width,maximum latewood density,minimum earlywood density,mean earlywood density and mean latewood density) were obtained from Picea crassifolia tree-ring samples from the west Qilian Mountains.The relationships between different tree-ring parameters and temperature were analyzed in this paper.It was found that there was a closest relationship between summer temperature(from June to September) and tree growth.The correlation analysis revealed that there was a significant relationship between precipitation and earlywood width during the period from June to July.The maximum density and average latewood density were not sensitive to climate change.This study demonstrated that the climatic information can be increased and the paleoclimate reconstruction can be improved by using both the tree ring width and tree ring density data.The results also indicated that it is important to understand the physiological properties of tree species and the local climatic conditions in reconstructing paleoclimate.The latewood width(LWW) and the earlywood width(EWW) were used to reconstruct the mean maximum temperature in Jiuquan from June to September during the period AD 1768-2007,and it can be used to explain the 46.6% of the total temperature variance.The estimated temperature revealed that there were 5 warm periods(1786-1836,1851-1885,1924-1933,1959-1967 and 1988-2007) and 5 cold periods(1768-1785,1837-1850,1886-1923,1934-1958 and 1968-1987),1893(25.47 ℃) and 1961(27.47 ℃) were the most extreme years,and the 1810s and 1890s were the most extreme decades.The estimated temperature values in northwest China were compared with the historical data.Climate warning during the period of 1988-2007 was a negative impact to tree radial growth.The multitaper method(MTM) spectral analysis indicated that there were some interannual cycles for 36.6,11.3,6.1,4.8,3.4,3.0,2.6 and 2.4 years in Jiuquan.Wavelet analysis indicated that there were the 20-40-year climatic cycles in the 20th century.The abrupt change of temperature occurred in 1804,1824,1852,1886,1906,1934,1971 and 1985 respectively.