Reduced precipitation variability over mid–latitude East Asia during the Pliocene-Pleistocene Transition

The trend of hydroclimatic variability represents a major area of concern in the context of global warming. The Pliocene–Pleistocene Transition (PPT) provides a valuable geological analogue, characterized by a dramatic shift in global ice volume and temperature. Here we present a pollen-based quantitative summer precipitation record spanning 3.4–2.4 Ma, derived from a fluvio-lacustrine sequence from the Datong Basin in the mid-latitude East Asia. Pollen data were converted to precipitation estimates using a pollen-derived Weighted Averaging Partial Least Squares (WA-PLS) model. Our results show that the summer precipitation remained broadly stable across the PPT, with no clear long-term trend. Instead, pronounced changes occur in precipitation variability. Before ~2.9 Ma, the late Pliocene hydroclimate showed large-amplitude fluctuations, with more frequent wet and dry extremes. After 2.9 Ma, variability decreases, and extreme values became less frequent, indicating a transition to a more stable rainfall regime. Spectral analyses further support this regime shift in the frequency domain: while ~100-kyr eccentricity-scale variability dominated the late Pliocene hydroclimate, it weakened and became less coherent following 2.9 Ma. Under future warming scenarios, these results imply that changes in hydroclimatic variability may represent a critical source of risk to mid-latitude Asian climate systems.