Tree-ring Recorded Climate Change In Southeastern Tibetan Plateau

High-resolution, accurate and mature dating technology makes tree-ring become one important climate proxy and have been applied for the past climate change researches. Tree-ring samples are widly distributed and easy to be collected, therefore the climate researches based on tree-ring data played a significant role for the global change studies in the past.Collected tree-ring samples from southeastern Qinghai-Tibetan Plateau and analysised the tree radii growth’s response to the monthly mean temperature and precipitation change, we reconstructed the climate change history in this area. Understanding the district’s climate change characters and roles has significant realistic meanings to the global change and local reaction studies.Core samples were collected from different species, and their standard chronologies were developed. Correlation between the tree-ring data and the monthly temperature and precipitation from the local meterological stations revealed that those tree-ring chronologies from high elevation are highly correlated with temperature and those from low elevation are highly correlated with rainfall change. Moisture in the early period of the grow season, especially the precipitation in late spring and early summer, is the main limit factor of the tree growth in this area. Comparing with the response pattern of different tree species, results showed that tree-ring sampes of same species had a similar growth-climate response pattern in different regions, and different species showed a nearly same growth-climate response in the.neighboring regions.Abies squamata tree-ring records from the north part of the study area was highly positive correlated with June-July average temperature, therefore we developed a chronology based on these samples and reconstructed more than500years’ early summer temperature change history. The reconstruction explained51.2%of the instrumental variances.Seven cold periods and five warm periods could be foung in the reconstruction results. That agrees well with nearby’s tree ring based temperature reconstructions. Spatial correlation analyses suggested that our reconstruction could represent the early summer temperature change of southeastern Qinghai-Tibetan Plateau well. The spectral results, which showed significant peaks at about2-6,1151,102and205years, revealed the temperature variability in this area may be affected by ENSO and solar activity.A nearly500-year reconstruction of precipitation in the southeast of the Qinghai-Tibet Plateau was developed based on fir samples collected from the Hengduan Mountains. Correlation analysis between the tree-ring chronology and the climate change data showed that moisture is the main limiting factor for the trees’ growth in this region. Ring-widths were significantly correlated with the Palmer Drought Severity Index and precipitation in many months. And the highest correlation coefficient is found between the annual growth of trees and rainfall from previous September to current June (0.738). Based on this relationship, we reconstructed the precipitation history from1509to2006. The reconstruction explains54.4%of the actual precipitation variation. In the reliable period (1549-2006) of the reconstruction, some low-frequency climate signal was included and indicating this region has been getting wetter in the last20years. There are6apparent dry and5pluvial periods in this reconstruction, and the drought period lasted longer in the17th century than other time. Compared with other works done recently, the reconstructed chronology shows a similar drought/hum idn ess variation trend. Further spatial correlation analysis confirms that the reconstructed precipitation could represent the rainfall history of the total Hengduan Mountains. Spectral analysis reveals that the precipitation in this area had significant spectral peaks in the years of3-5,60and79-85years.Compared tree-ring chronologies of the northern and the southern part of the Qinghai-Tibet Plateau which were affected by the May and June’s water stress, we found their tree-ring chronologies had obvious district difference. Opposite change periods could be found in the the low-frequency variations, and it was highlighted in the last a few decades. Drive mechanism of this phenomenon needs further study.