Tree-ring Based Climate Reconstruction For Western Sichuan Plateau

The challenges of global change, such as desertification of land in arid area,glacial recession, sea level rise, increase in frequency and strength of extreme weather and climate events, gradually show its influence on human survival environment.Climate change is a major content of global change, especially at decade to multi-decadal scales over the last millennium. High-resolution reconstruction of climate change history and research of regional climate response has significant meaning for the survival and development of contemporary human society.Western Sichuan Plateau is located in the southeast of the Qinghai-Tibet Plateau,the transition zone between the second and third steps of topography in China, further on, it’s located in the transition zone of Qinghai-Tibet high code region and the eastern monsoon region, which were two of the three large climate province of China,and because of which it responses sensitively to climate change. However, due to the complexity of the background of local climate environment, the existing research is insufficient to sketch a compete picture of climate change history in this region, which mainly manifest as shortage of discussion on modern climate differentiation, together with region-based diversity of the relationship between tree growth and climate variation.This study collected tree ring samples from 4 sites and gathered data from another 8 sites investigated by predecessors, as materials in the research of relationships between tree growth and climate change based on current climate region division, together with high resolution reconstruction of regional climate change during historical period, so as to provide reference for local ecological protection, and to provide basic data for the research of climate change on Western Sichuan Plateau.Empirical Orthogonal Function(EOF) decomposition method and clustering method with correlation coefficient as its distance/data matrix were applied to detect the spatial distribution feature of measurement meteorological data, leading to a same result of climate district division, which divided Western Sichuan Plateau into two districts, the southwest and northeast area, we calculated the average climate factors for both two regions, for purpose of further climate response analysis and climate reconstruction.Correlation and response analysis were conducted between each chronology and its related regional climate factors, the result indicated that response pattern of tree growth and climate factors was relatively complicated, possibly affected by altitude,local topography, distance to a river and the relative position of the sample site with a tall mountain nearby, etc. Thus, chronology combination should be with caution.We selected some single chronologies sensitive to climate change to establish regional climate reconstruction, in this way, we reconstructed annual mean minimum temperature, average maximum temperature in late summer and early autumn, late autumn and early winter average temperature, and precipitation in January of southwest region, in the meantime, we reconstructed the annual mean minimum temperature of northeast region of Western Sichuan Plateau.Period analysis found 11 years and 22 years solar active period in the reconstructed climate factors, which suggested that climate change in the study area may be affected by solar activity. In addition, decadal fluctuations were also detected in the reconstructed series, which may be related to the Atlantic SST anomaly.Comparison with reconstructed Atlantic Multi-decadal Oscillation index and spatial correlation analysis between the average minimum temperature and the global sea surface temperature support this point of view in some degree, but response patterns of southwest and northeast region of Western Sichuan Plateau is different, the specific mechanism needs further research.