The Yellow River has caused suffering to people with its devastating floods throughout human history. Understanding the occurrence of Yellow River floods and their relationship with climate change is crucial for sustainable water governance in North China. Here we synthesize historical and climatic records in the Yellow River basin to investigate their relationship during the past two millennia. Based on historical archives of river floods and levee breaches, we developed a decadally resolved Yellow River flooding frequency record from 221 BCE to 1949 CE, which provides a rare chance to perceive the river’s long-term flood dynamics. As revealed, the Yellow River flooding can be divided into two distinct stages: an early stage of low-frequency floods from the 220s BCE to the 890s CE; and a late stage of high-frequency floods during the 900s–1940s CE. A substantial increase in flooding frequency around the 10th century fell within the transition period into the Medieval Climate Anomaly (MCA), during which the Yellow River basin featured warm and wet climate conditions. Coincidentally, human management of the Yellow River intensified as a response to more severe and frequent floods. The intense river management persisted thereafter and resulted in the super-elevation of the riverbed, which made the river more prone to flooding. Consequently, the Yellow River flooding frequency remained high even after entering the Little Ice Age, during which the river basin featured cool temperature and reduced precipitation. Our study suggests that the dramatic transition from a previous cool, dry into a warm, wet climate during the MCA period triggered intense human management of river channels and the establishment of the flood-prone nature of the Yellow River.

Scarcity of high-resolution proxy records has hindered our understanding of long-term climate variations and their mechanism in climate-sensitive regions such as the Tibetan Plateau (TP). In this study, we present a winter minimum temperature (Tmin) reconstruction for the past 351 years (1648–1998) based on a composite tree ring width chronology from three upper treeline sites in the Gongga Mountains, southeastern TP. Despite a loss of sensitivity to winter Tmin after the 1990s, tree growth agrees well with previous December to current March (pDec-cMar) Tmin during 1953–1998, and a regression model based on climate-tree growth relationship over this period explains 52% of the instrumental Tmin variance. The resulting reconstruction exhibits three major cold (1670–1745, 1805–1853, and 1877–1949) and four major warm (1648–1669, 1746–1804, 1854–1876, and 1950–1998) periods over the past four centuries. Long-term winter Tmin variations in the Gongga Mountains have high coherence with those represented by temperature reconstructions in the nearby regions. Together, they indicate close association of the reconstructed warm/cold periods with the positive/negative phases of the Atlantic Multidecadal Oscillation (AMO), suggesting that the AMO may have been a key driving force affecting regional climate over the past few centuries.

Tree-ring chronologies were developed for Sabina saltuaria and Abies faxoniana in mixed forests in the Qionglai Mountains of the eastern Tibetan Plateau. Climate-growth relationship analysis indicated that the two co-existing species reponded similarly to climate factors, although S. saltuaria was more sensitive than A. faxoniana. The strongest correlation was between S. saltuaria chronology and regional mean temperatures from June to November. Based on this relationship, a regional mean temperature from June to November for the period 1605–2016 was constructed. Reconstruction explained 37.3% of the temperature variance during th period 1961–2016. Six major warm periods and five major cold periods were identified. Spectral analysis detected significant interannual and multi-decadal cycles. Reconstruction also revealed the influence of the Atlantic Multi-decadal Oscillation, confirming its importance on climate change on the eastern Tibetan Plateau.

Tree-ring blue intensity (BI) has been widely applied for temperature reconstructions in many regions around the globe. However, it remains untested in the southeastern Tibetan Plateau (TP) where a large number of ancient trees are distributed. In this study, we developed earlywood blue intensity (EWBI), latewood blue intensity (LWBI), and delta blue intensity (ΔBI) chronologies based on tree-ring samples collected from Abies spectabilis at two sites in the southeastern TP. Our results reveal that the EWBI and ΔBI chronologies correlated negatively with temperature parameters and LWBI chronology correlated positively with temperature parameters, respectively. Among them, the LWBI chronology was identified most suitable for reconstructing the mean temperature in August. A linear regression model was developed for the August temperature reconstruction, which accounts for 34.31% of the observed variance in the period of 1954–2017. The reconstruction, spanning 1789–2017, is highly consistent with other tree-rings based temperature reconstructions from the neighboring regions. Our findings reveal a potential linkage between the August temperature anomaly in the southeastern TP and the Atlantic Multidecadal Oscillation (AMO), which suggests that the AMO fingerprint in the region is not just evident in winter but also in summer.