Summer Mean Temperature Reconstruction During The Past 285 Years Based On Tree-Ring In Northern Gaoligong Mountains, Northwestern Yunnan Of China

Historical temperature reconstructions enable us to understand the long-term thermal variation feature of a region. We developed a tree-ring width chronology of the coniferous species Tsuga dumosa (D. Don) Eichler (Himalayan Hemlock) growing in the northern Gaoligong Mountains, northwestern Yunnan province of China. The climate-tree growth relationship analysis indicated that summer mean temperature was the main limiting factor of the radial growth of Himalayan Hemlock. Accordingly, using a linear regression model, we reconstructed the historical summer mean temperature time series spanning A.D. 1720-2005, which could account for 35.56% of the observedtemperature variance. Based on the reconstruction, the most obvious warme periods were identified as 1715-1730s, 1900-1910, 1920-1940 and 1980-2005, while the main cold episodes were 1740s-1750s, 1810s-1830s, 1910s-1920s and 1940s-1970s. Wavelet and correlation analyses indicated the existence of several interannual (2-4 years and 5.5 years) and decadal (8-12years) cycles in the variation of summer mean temperature, which probably related to El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and solar activity.