Assessing the Regional Climate Response to Different Hengduan Mountains Geometries With a High‐Resolution Regional Climate Model

The Hengduan Mountains (HM) are located on the southeastern edge of the Tibetan Plateau and feature high mountain ridges (>6,000 m MSL) 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 period 2001–2005. We conduct one control simulation with modern topography and two idealized 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 deep valleys 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. Plain Language Summary The Hengduan Mountains (HM), located on the southeastern edge of the Tibetan Plateau, feature high mountains separated by deep valleys. They also exhibit a particularly high biodiversity, which is believed to be caused by the interaction of mountain formation and climate. To understand the impact of HM geometry on local climate, we perform high‐resolution atmospheric simulations with different HM shapes. We conduct one experiment with modern topography and two idealized experiments with modified topographies inspired by past geology: one where the mountains' elevation is lowered and another one where the deep valleys are filled. The first experiment reveals that the uplift of the HM leads to a local precipitation increase of ∼25%, with remote effects of enhanced precipitation in Indochina