Moisture history in the Northeast China since 1750s reconstructed from tree-ring cellulose oxygen isotope

Northeast China has suffered many serious droughts, with loss of agricultural production. A lack of long-term monitoring data has hindered our understanding of drought characteristics and mechanisms. The moisturerelated history of the region was investigated by constructing a tree-ring cellulose 618O chronology for the period 1752-2015 using samples collected from four Korean pine (Pinus koraiensis) trees in eastern NE China. Results indicate that tree-ring 618O values are significantly correlated with summer (June-September) precipitation, relative humidity, and drought severity. The tree-ring 618O chronology accounts for 50.7% of the observed variance in summer relative humidity and was used to reconstruct regional relative humidity levels back to 1752. Compared with previous reconstructions of drought-related changes in NE China, the reconstruction reveals more high- and low-frequency variability, with two drought periods during the 1750s-1820s and 1960s-2015, and a wet period during 1820-1960. Regional drying trends is mainly influenced by a weakened East Asia summer monsoon (EASM), with both drought periods being concurrent with high temperatures and a weak EASM. Together with the global warming trend, the increasing temperature and associated precipitation reduction in NE China indicates increasing likelihood of drought for the region in future.