Abstract: The northeastern permafrost region of China is one of the most vulnerable areas to climate warming in mid-latitude areas. Despite this, the specific pathways of water vapor circulation and transport in this area remain poorly understood. Additionally, there is ongoing debate on whether the oxygen isotope of precipitation (δ¹⁸O_p) is primarily influenced by the temperature or the precipitation amount effects. Tree-ring samples were collected from various sites and tree species across the region, and 12 stable oxygen isotopes (δ¹⁸O_c) series constructed to investigate the water vapor signals embedded within. Our findings revealed consistent δ¹⁸O_c variations across different sites and species, reflecting relative humidity signals during the growing season (June to September) (r =  − 0.764, P < 0.001, n = 40). By applying an improved model to simulate δ¹⁸O_p, a “temperature effect” was identified. Both δ¹⁸O_c and δ¹⁸O_p provided valuable insights into the regional water vapor circulation, with δ¹⁸O_c offering a stronger climate signal. A binary linear regression model further revealed that δ¹⁸O_p had a greater influence on δ¹⁸O_c than relative humidity. The regional climate is primarily driven by the East Asian summer monsoon and large-scale water vapor circulation associated with the El Niño-Southern Oscillation. Because of future warming and drying trends, trees in this region are expected to face increasing drought stress.

Key words: Tree-ring oxygen isotopes, Precipitation oxygen isotopes, Improved model, Permafrost region