Influence of Asian Monsoon Dynamics on Precipitation Characteristics of the Eastern Tibetan Plateau in Cold and Warm Climates: Insights from a Regional Climate Model

The Hengduan Mountains region (HM), located in the Eastern Tibetan Plateau, is renowned for its rich biodiversity. High-resolution climate data from past periods are essential for gaining deeper insights into the ecological and evolutionary processes that have shaped this unique and diverse region. In this study, we applied the non-hydrostatic limited-area model COSMO, with a resolution of 12 km over East Asia, to simulate two distinct climatic periods: the mid-Pliocene (~3 Ma), representing a warmer period, and the Last Glacial Maximum (LGM; ~21 ka), a colder period, both compared to present-day conditions.

Our results reveal that, despite contrasting changes in moisture supply, both warm and cold periods experienced a weakened Indian summer monsoon, attributed to the exposure of the Indochina continental shelf during these times—caused by sea-level drops during the LGM and dynamic topography during the mid-Pliocene. During the mid-Pliocene, an earlier northward migration of the Western Jet led to an earlier onset of the Indian summer monsoon and a wetter spring in the HM. In contrast, the HM experienced increased precipitation during the LGM in both summer and winter. Increased summer precipitation was driven by enhanced moisture supply from the south, while enhanced winter precipitation, primarily in the form of snowfall at high elevations, was associated with more unstable atmospheric stratification.

The local precipitation characteristics of the HM are thus influenced by the interplay between large-scale atmospheric dynamics and regional topographical features such that, in contrast to most mid-latitude regions, the HM did not experience drying and wetting during glacial-interglacial cycles. The stability of mean precipitation across different climatic periods likely played a pivotal role in supporting the HM's high biodiversity, providing a stable and moist environment conducive to supporting diverse ecosystems.