Tree-ring δ18O-based July–August relative humidity reconstruction on Mt. Shimen, China, for the last 400 years

Abstract

Understanding long-term drought variations in the past can help us to evaluate ongoing and future hydroclimate changes in the arid western Chinese Loess Plateau. The present study generated a new stable oxygen isotope (δ18O) chronology composed of five individual Pinus tabulaeformis Carr. isotope series from Mt. Shimen, China. Correlation function analysis revealed that the composite tree-ring δ18O series responded significantly to July–August relative humidity (RHJA, r = −0.684, n = 47, p < .0001). A transfer function was thus designed, and the RHJA in the Mt. Shimen region was reconstructed for the past 397 years. Several famous droughts in Chinese history, such as the Chong Zhen severe drought (1637–1643 CE), Ding Wu extraordinary drought (1876–1878 CE) and 1928–1930 CE severe drought, are captured by our reconstruction. Meanwhile, our reconstructed RHJA compares well with other palaeoclimatic results around the study area. Spatial correlation analysis revealed that the RHJA reconstruction displays large-scale representativeness. The reconstruction is significantly positively correlated with several Asian summer monsoon (ASM) indices, indicating that the reconstructed RHJA reflects the variations in ASM intensity to a large extent. In terms of the local climate change mechanisms, we found that the factors affecting the variations in RHJA in the Mt. Shimen region are complex and involve large-scale oceanic–atmospheric couplings, such as sea surface temperature (SST), El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO). Solar activity also certainly has great impacts.