To better understand the landscape dynamics and changes in habitat connectivity influenced by glacial and interglacial oscillations over the biodiversity-rich Hengduan Mountains (HM) region, high-resolution climate data for past periods are essential. We apply the non-hydrostatic limited-area model COSMO, with a resolution of 12 km over East Asia, to simulate the Last Glacial Maximum (LGM), a period characterized by a generally colder and drier climate compared to present-day conditions. We perform the downscaling with a novel approach for paleoclimate modelling, the Pseudo-Global Warming (PGW) method. The COSMO PGW simulation for the LGM shows that COSMO generally replicates the large-scale dynamics of the driving global climate model simulation in the colder climate. Both models suggest weaker Asian summer monsoon systems during this period. Consequently, regions such as the Bay of Bengal, and the South China Sea, which typically receive substantial monsoon rainfall, experience significantly reduced precipitation. However, despite these model similarities, the high-resolution COSMO simulation exhibits distinctive differences on a smaller scale—particularly over land. For instance, COSMO suggests a more pronounced southward shift of the jet stream during the LGM winter, with cooler conditions in southern China. Moreover, the COSMO simulation, despite the overall weaker summer monsoon circulation, features increased precipitation amounts for much of the HM. Additionally, COSMO suggests a more extensive increase in snowfall over the High Mountain Asia region. Our study suggests that the resource-saving PGW approach is a suitable method to bridge the gap between large-scale projections and regional climate impacts—also for past periods like the LGM.

The Hengduan Mountains (HM) are located on the southeastern edge of the Tibetan Plateau (TP) and feature high mountain ridges (> 6000 m a.s.l.) separated by deep valleys. The HM region also features an exceptionally high biodiversity, believed to have emerged from the topography interacting with the climate. To investigate the role of the HM topography on regional climate, we conduct simulations with the regional climate model COSMO at high horizontal resolutions (at ~12 km and a convection-permitting scale of ~4.4 km) for the present-day climate. We conduct one control simulation with modern topography and two idealised experiments with modified topography, inspired by past geological processes that shaped the mountain range. In the first experiment, we reduce the HM’s elevation by applying a spatially non-uniform scaling to the topography. The results show that, following the uplift of the HM, the local rainy season precipitation increases by ~25%. Precipitation in Indochina and the Bay of Bengal (BoB) also intensifies. Additionally, the cyclonic circulation in the BoB extends eastward, indicating an intensification of the East Asian summer monsoon. In the second experiment, we remove the deep valley by applying an envelope topography to quantify the effects of terrain undulation with high amplitude and frequency on climate. On the western flanks of the HM, precipitation slightly increases, while the remaining fraction of the mountain range experiences ~20% less precipitation. Simulations suggest an overall positive feedback between precipitation, erosion, and valley deepening for this region, which could have influenced the diversification of local organisms.