A 243‐Year Tree‐Ring δ 18 O Record Reveals Shifts in Summer Moisture Regime and Large‐Scale Atmospheric Drivers in the Northernmost Taiga of China

Abstract The Mohe region, situated in northeastern China at the southern boundary of both the global taiga biome and the continuous permafrost zone, is highly sensitive to climate change but remains underrepresented in long‐term climatic records. To bridge this gap, we developed a 243‐year stable oxygen isotope (δ 18 O) chronology from Larix gmelinii tree rings in the northernmost China’s Taiga, constituting the δ 18 O‐based hydroclimate reconstruction for this climatically critical area. Statistical analysis revealed a significant negative correlation between δ 18 O values and summer (June–September) relative humidity (RH) ( r = −0.719, R 2 = 0.517), enabling a robust reconstruction of RH from 1781 to 2023. The reconstruction indicates that prior to the 20th century, RH was generally higher and predominantly characterized by persistent, long‐lasting wet periods. In contrast, the period after the 20th century was marked by more frequent drought events, which were shorter in duration and more irregularly distributed. Spectral and wavelet analyses reveal pronounced interannual (2–7 years) and interdecadal (10–30 years) variability, primarily modulated by large‐scale atmospheric circulation patterns associated with the El Niño‐Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). These findings underscore the combined influence of Pacific and Atlantic moisture sources on hydroclimatic variability in Northeast Asia and provide a critical baseline for assessing the impacts of contemporary and future climate change in the mid‐to high latitudes permafrost‐affected forest ecosystems.