Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ¹⁸O of tree-ring cellulose

Abstract

Abstract. We present an 800 years long δ18O chronology from the eastern part of the Tibetan Plateau (TP). The chronology dates back to 1193 AD and was sampled in 1996 AD from living Juniperus tibetica trees. The chronology is unique for eastern Tibet and provides a reliable archive for hydroclimatic reconstructions. Highly significant correlations were obtained with air moisture (relative humidity, vapour pressure and precipitation) during the summer season. We applied a linear transfer model to reconstruct the summer season relative humidity variation over the past 800 years. We identified more moist conditions at the termination of the Medieval Warm Period, an oscillating air humidity around the mean during the Little Ice Age and a sudden decrease of relative humidity since the 1870s. The late 19th century humidity decrease is in good accordance with several multiproxy hydroclimate reconstructions for south Tibet. On the other hand, since the end of the 19th century strong evidences for an increase in humidity on the northern TP is exhibited. Spatial correlation analysis with the North Atlantic Oscillation index (NAO) and the sea surface temperature (SST) of Niño region 3.4 reveal a weak and nonstationary relationship to the δ18O chronology. Instead, spatial correlations expose a dominating convective influence to the relative humidity reconstruction. Furthermore, wavelength analysis reveal good agreements between the significant cyclicities in our δ18O chronology and several moisture sensitive proxy archives.