Jinpeng Zhang, Baijun Ji, Nini Xiao, Xiangyu Duan, Min Zhang, Yangbin Shi, Weihua Luo. Findings of the Association for Computational Linguistics: ACL-IJCNLP 2021. 2021.

Since the 1950s, divergence problems have reduced the temporal stability of tree rings in response to climate, shaken the foundations of dendroclimatology, and affected the reliability of reconstructed models based on tree rings and the accuracy of historical climate series. Therefore, it is of great importance to investigate divergence problems, which will help us to better understand the growth strategies of trees in response to climate warming and provide a scientific basis for accurate climate reconstruction and simulation of forest dynamics. This paper aims to elucidate the mechanism of divergent growth of Picea schrenkiana at high altitudes in the western Tianshan from three aspects: variations in atmospheric circulation, changes in climatic factors, and the coping strategy of trees with climate change. High spring temperatures accelerate the melting of snow cover. Large amounts of snowmelt initially replenish soil water, leading to the rapid growth of trees, but later, the continuous consumption of snowmelt reduces the available water capacity of soil, resulting in water stress on trees. The pattern of trees’ response to changes in climate ranges from a pure temperature limitation to a collaborative temperature–moisture limitation. Since the 1990s, the weakening of the westerly circulation and the North Atlantic Oscillation has reduced their impacts on the hydroclimate in the Tianshan Mountains of Central Asia. The combination of heat-induced water deficit and a long-term weakening trend in atmospheric circulation has slowed tree growth over the past decade.

The inter-annual stable carbon isotope ratio (δ¹³C) of three tree-ring cores of P. euphratica (Populus euphratica Oliv.) was determined from Ejina Oasis in Northwest China. A robust and representative δ¹³C chronology is generated from the three δ¹³C series using an arithmetic mean method. After eliminating the influence of the δ¹³C from elevated atmospheric carbon dioxide (CO₂) concentration, we obtained a carbon isotopic discrimination (Δ¹³C) chronology. According to the significant correlation between the tree-ring Δ¹³C and instrumental data, we reconstructed the mean maximum temperature anomalies from previous December to current September (T_DS) for the period 1901–2011. The reconstruction explained 43.6% of the variance over the calibration period. Three high-temperature periods (1929–1965, 1972–1974, and 1992–2006) and three low-temperature periods (1906–1926, 1966–1968, and 1975–1991) were found in the reconstructed series. Comparisons between the reconstructed T_DS and the observed mean temperature from previous December to current September in Anxi meteorological station and the temperature index in north-central China demonstrated the reconstructed T_DS has the advantage of reliability and stability. The significant spatial correlation declared that the reconstruction has a broad spatial representation and can represent the temperature variation characteristics in a wide geographical area. In addition, we found that the area of Ejina Oasis is smaller (larger) when the mean maximum temperature is higher (lower), which may be due to a conjunction effect of natural and anthropogenic activities. Significant periodicities and correlations suggested that the T_DS variations in Ejina Oasis were regulated by solar radiation and atmospheric circulations at the interannual and interdecadal time scales.

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.