Tree-ring-based reconstruction of temperature variability (1445-2011) for the upper reaches of the Heihe River Basin, Northwest China

Long-term temperature variability has significant effects on runoff into the upper reaches of inland rivers. This paper developed a tree-ring chronology of Qilian juniper (Sabina przewalskii Kom.) from the upper tree-line of the middle Qilian Mountains within the upper reaches of Heihe River Basin, Northwest China for a long-term reconstruction of temperature at the study site. In this paper, tree-ring chronology was used to examine climate-growth associations considering local climate data obtained from Qilian Meteorological Station. The results showed that temperatures correlated extremely well with standardized growth indices of trees (r=0.564, P < 0.001). Tree-ring chronology was highest correlated with annual mean temperature (r=0.641, P < 0.0001). Annual mean temperature which spans the period of 1445-2011 was reconstructed and explained 57.8% of the inter-annual to decadal temperature variance at the regional scale for the period 1961-2011. Spatial correlation patterns revealed that reconstructed temperature data and gridded temperature data had a significant correlation on a regional scale, indicating that the reconstruction represents climatic variations for an extended area surrounding the sampling sites. Analysis of the temperature reconstruction indicated that major cold periods occurred during the periods of 1450s-1480s, 1590s-1770s, 1810s-1890s, 1920s-1940s, and 1960s-1970s. Warm intervals occurred during 1490s-1580s, 1780s-1800s, 1900s-1910s, 1950s, and 1980s to present. The coldest 100-year and decadal periods occurred from 1490s-1580s and 1780s-1800s, respectively, while the warmest 100 years within the studied time period was the 20(th) century. Colder events and intervals coincided with wet or moist conditions in and near the study region. The reconstructed temperature agreed well with other temperature series reconstructed across the surrounding areas, demonstrating that this reconstructed temperature could be used to evaluate regional climate change. Compared to the tree-ring reconstructed temperature from nearby regions and records of glacier fluctuations from the surrounding high mountains, this reconstruction was reliable, and could aid in the evaluation of regional climate variability. Spectral analyses suggested that the reconstructed annual mean temperature variation may be related to large-scale atmospheric-oceanic variability such as the solar activity, Pacific Decadal Oscillation (PDO) and El Nio-Southern Oscillation (ENSO).