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In summer 2020, extreme rainfall occurred throughout the Yangtze River basin, Huaihe River basin, and southern Yellow River basin, which are defined here as the central China (CC) region. However, only a weak central Pacific (CP) El Niño happened during winter 2019/20, so the correlations between the El Niño–Southern Oscillation (ENSO) indices and ENSO-induced circulation anomalies were insufficient to explain this extreme precipitation event. In this study, reanalysis data and numerical experiments are employed to identify and verify the primary ENSO-related factors that cause this extreme rainfall event. During summer 2020, unusually strong anomalous southwesterlies on the northwest side of an extremely strong Northwest Pacific anticyclone anomaly (NWPAC) contributed excess moisture and convective instability to the CC region, and thus, triggered extreme precipitation in this area. The tropical Indian Ocean (TIO) has warmed in recent decades, and consequently, intensified TIO basinwide warming appears after a weak El Niño, which excites an extremely strong NWPAC via the pathway of the Indo-western Pacific Ocean capacitor (IPOC) effect. Additionally, the ENSO event of 2019/20 should be treated as a fast-decaying CP El Niño rather than a general CP El Niño, so that the circulation and precipitation anomalies in summer 2020 can be better understood. Last, the increasing trend of tropospheric temperature and moisture content in the CC region after 2000 is also conducive to producing heavy precipitation.

As one of the regions most affected by global climate warming, the Tianshan mountains has experienced several ecological crises, including retreating glaciers and water deficits. Climate warming in these mountains is considered mainly to be caused by increases in minimum temperatures and winter temperatures, while the influence of maximum temperatures is unclear. In this study, a 300-year tree-ring chronology developed from the Western Tianshan Mountains was used to reconstruct the summer (June–August) maximum temperature ( T max6–8 ) variations from 1718 to 2017. The reconstruction explained 53.1% of the variance in the observed T max6–8 . Over the past 300 years, the T max6–8 reconstruction showed clear interannual and decadal variabilities. There was a significant warming trend (0.18 °C/decade) after the 1950s, which was close to the increasing rates of the minimum and mean temperatures. The increase in maximum temperature was also present over the whole Tianshan mountains and its impact on climate warming has increased. The T max6-8 variations in the Western Tianshan mountains were influenced by frequent volcanic eruptions combined with the influence of solar activity and the summer North Atlantic Oscillation. This study reveals that climate warming is significantly influenced by the increase in maximum temperatures and clarifies possible driving mechanisms of temperature variations in the Western Tianshan mountains which should aid climate predictions.

Given growing concerns about global climate change, it is critical to understand both historical and current shifts in the hydroclimate, particularly in regions critically entwined with global circulation. The Tibetan Plateau, the Earth’s largest and highest plateau, is a nexus for global atmospheric processes, significantly influencing East Asian hydroclimate dynamics through the synergy of the Asian Monsoon and the Westerlies. Yet, understanding historical and recent hydroclimate fluctuations and their wide-ranging ecological and societal consequences remains challenging due to short instrumental observations and partly ambiguous proxy reconstructions. Here, we present a precisely-dated 3476-year precipitation reconstruction derived from tree-ring δ 18 O data on the Tibetan Plateau, representing one of the few multi-millennia-long annually-resolved terrestrial δ 18 O records to date. Our findings reveal that the 20 th  century drought extremes are severe within the past three millennia, and likely linked to the weakening of both the Asian Monsoon and Westerlies due to anthropogenic aerosol emissions. Additionally, our analyses identified three distinct stages (110 BC–AD 280, AD 330–770 and AD 950–1300) characterized by shifts toward arid hydroclimate conditions, corresponding to significant social unrest and dynasty collapses, which underscores the potential societal impacts of severe hydroclimatic shifts. An annually resolved 3476-year tree-ring record from the Tibetan Plateau reveals severe 20 th  century droughts and highlights the interplay between the Asian Monsoon and Westerlies. Droughts are often linked to the collapse of dynasties.

The far-reaching impacts of central Pacific El Niño events on global climate differ appreciably from those associated with eastern Pacific El Niño events. Central Pacific El Niño events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NIÑO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Niño4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Niño-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies. El Niño events in the Central Pacific may be changing due to climate change, but long records to support this are lacking. Here, the authors present sea surface temperature reconstructions from tree cellulose for the last 800 years which suggest the variability of Central Pacific El Niño events has increased.

In the context of global warming, the “divergence problem” phenomenon in the climate response of tree growth has been observed. Here, we use tree-ring stable oxygen isotopes (δ 18 O) to examine the response under current warming in Tsuga chinensis Pritz. and Pinus tabulaeformis Carr. growing on the south slope (SS) and north slope (NS) of the Qinling Mountains, a boundary between subtropical and warm temperate zones in China. Both δ 18 O series are significantly correlated with several hydroclimate reconstructions in the surrounding area since 1750, suggesting that tree-ring δ 18 O could capture large-scale characteristics of climate change in the Qinling Mountains. However, a difference arises in the two δ 18 O series since the early 1980s. At the SS site, the increasing δ 18 O is closely related to the increased warming (0.30℃/year) from 1981. This result mainly because temperature is the most significant climate factor (r = 0.465, n = 51, p < 0.001) in determining tree-ring δ 18 O by affecting the δ 18 O of soil water before and after the increased warming at the SS site. Although the warming trend is also significant (0.31℃/year) at the NS site since 1981, the δ 18 O variation shows no obvious fluctuation, which may indicate that relative humidity is the dominant controlling factor (r=-0.603, n = 48, p < 0.001) but not temperature for the δ 18 O of Pinus tabulaeformis . The results imply that tree-ring δ 18 O is still sensitive to its dominant climatic controlling factor under the current warming, suggesting that it has the potential to infer past climate change by using tree-ring δ 18 O in a future warming scenario.

By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average tem- peratures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the "Eastern Jin Event", occurred from 348 AD to 413 AD. Calculation re- sults show that the temperature variations over the mid-eastern Tibetan Plateau are not only repre- sentative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s.

The historical May-October mean temperature since 1831 was reconstructed based on tree-ring width of Qinghai spruce (Picea crassifolia Kom.) collected on Mt. Dongda, North of the Hexi Corridor in Northwest China. The regression model explained 46.6% of the variance of the instrumentally observed temperature. The cold periods in the reconstruction were 1831-1889, 1894-1901, 1908-1934 and 1950-1952, and the warm periods were 1890-1893, 1902-1907, 1935-1949 and 1953-2011. During the instrumental period (1951-2011), an obvious warming trend appeared in the last twenty years. The reconstruction displayed similar patterns to a temperature reconstruction from the east-central Tibetan Plateau at the inter-decadal timescale, indicating that the temperature reconstruction in this study was a reliable proxy for Northwest China. It was also found that the reconstruction series had good consistency with the Northern Hemisphere temperature at a decadal timescale. Multi-taper method spectral analysis detected some low- and high-frequency cycles (2.3-2.4-year, 2.8-year, 3.4-3.6-year, 5.0-year, 9.9-year and 27.0-year). Combining these cycles, the relationship of the low-frequency change with the Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Southern Oscillation (SO) suggested that the reconstructed temperature variations may be related to large-scale atmospheric-oceanic variations. Major volcanic eruptions were partly reflected in the reconstructed temperatures after high-pass filtering; these events promoted anomalous cooling in this region. The results of this study not only provide new information for assessing the long-term temperature changes in the Hexi Corridor of Northwest China, but also further demonstrate the effects of large-scale atmospheric-oceanic circulation on climate change in Northwest China.

How hydroclimate will change in the future has been of great interest with the increasing concern of global warming. Acquirement of ample high-resolution proxy-based reconstructions will aid to answer such question by increasing the accuracy of climate prediction models. However, discrepancies among existing reconstructions in the southeast part of China (SEC) has aroused great uncertainty about the hydroclimatic conditions. Here we present an annually-resolved June–August scPDSI reconstruction and a June–July relative humidity reconstruction from 1876 to 2015 in the middle reaches of the Yangtz River, based on accurately-dated tree-ring materials. The reconstructions well reproduce the instrumental records, with explained variance of 48.82% and 46.79%. A secular wetting trend is found in the study area from 1876 to 2000, then it dried quickly. The driest (2006–2015) and wettest (1943–1955) periods both occurred after 1940, and 40% of the top 10 driest years occurred in the twenty-first century. Overall, an increasing intensified hydroclimatic variation is identified, especially significant in the recent decade. The historical summer hydroclimatic fluctuations, which were found closely related to the concurrent temperature variations, show broadly large spatial and temporal synchronicity with existing hydroclimatic reconstructions in SEC, while the intensity of variation is intermittently different. Hydroclimatic variation in the study area might be a comprehensive effect of Pacific Decadal Oscillation (PDO), Western Pacific Subtropical High (WPSH) and El Niño-Southern Oscillation (ENSO) variations. Our reconstruction provides additional support not only for a comprehensive understanding of the spatiotemporal characteristics of hydroclimatic variations, but also for the diagnosis and prediction of hydroclimatic anomalies.

As the capital city of China, Beijing is confronted with significant water scarcity challenges, primarily attributed to its substantial population growth and accelerated industrial expansion. The Miyun Reservoir, which serves as the principal water source for Beijing's domestic supply, is primarily replenished by the White River. Using Chinese pine (Pinus tabuliformis Carr.) tree‐ring samples collected near the upper reaches of river, we analyzed inter‐annual variations in δ18O, to access the variability of reservoir outflow discharge from 1961 to 2018. Statistical analysis revealed a significant positive correlation between tree‐ring δ18O and the mean minimum temperature during February‐March, demonstrating a pronounced “temperature effect” on isotopic fractionation associated with cellulose synthesis. A significant negative correlation was observed between δ18O and summer outflow discharge, primarily driven by the coupled effects of snowmelt dynamics on both hydrological regimes and isotopic partitioning processes. Tree‐ring δ18O record revealed distinct anthropogenic disturbances in outflow discharge patterns during two critical periods: 1976–1985 and 1997–2002, characterized by significant deviations from natural hydrological variability. Outflow discharge was found to be fundamentally modulated by the natural variability of large‐scale atmospheric circulation patterns.

A comprehensive understanding of the spatial characteristics of warming trends and temperature variability is important given global warming. Paleoclimate reconstruction has played an important role in evaluating warming and extreme climactic events in recent decades. Using the ring width of Pinus tabulaeformis , we reconstructed the ground surface temperature changes at Mengshan Mountain, in the central part of eastern China (EC), from 1667 to 2019. There were 3 extremely low-temperature years, 42 low-temperature years, 256 normal years, 37 high-temperature years and 15 extremely high-temperature years over the past 353 years. High and extremely high temperatures mainly occurred in the first half of the 19th century, the end of the 20th century and the beginning of the 21st century; low and extremely low temperatures occurred in almost all periods except for the last 50 years. By combining the past temperature reconstructions from the Great Xing’an Mountains in northern EC and Taiwan in southern EC, we also found that after the start of the Anthropocene, there were strong positive correlations among the temperatures of the northern, central and southern parts of EC. However, before the Anthropocene, these correlations were weak, and there was even a significant negative correlation during some periods. Additionally, the temperature in EC exhibited different change patterns before and during the Anthropocene. Before the Anthropocene, the temperature in southern EC showed an upward trend; in central EC, the temperature first rose and then began to decline in the 1820s; there was no obvious trend in the temperature changes in northern EC. The spatial consistency of temperature changes during the Anthropocene might be related to the fact that greenhouse gases emitted by human activities diffuse evenly withatmospheric circulation and absorb longwave radiation to directly heat the atmosphere.