Modeling Eocene Asian climate with geologically revised paleogeography

The Eocene was one of the warmest intervals of the Cenozoic, during which the Asian hydroclimate reorganized alongside major tectonic and paleogeographic changes. Yet, large uncertainties in the paleotopography of Eocene Asia—particularly across the Tibetan region—continue to obscure how continental dry–wet patterns evolved under greenhouse conditions. Here, we investigate the hydroclimatic evolution of the Eocene using a fully coupled climate simulation with revised paleogeographic boundary conditions, incorporating updated geological constraints on Asian paleogeography, including Tibetan paleotopography and the timing of the India–Asia collision. We reconstruct boundary conditions for the early (53 Ma) and late Eocene (38 Ma) featuring a characteristic “two-mountains–one-basin’’ configuration. The simulations reproduce a major transition from an extensive zonal arid belt in the early Eocene (53 Ma) to a more heterogeneous and generally wetter regime by the late Eocene (38 Ma), broadly consistent with available proxy evidence. By decomposing logarithmic changes in the aridity index into precipitation and evaporative-demand components, we show that late Eocene wetting arises from the combined effects of enhanced precipitation and reduced evaporative demand, with their relative importance varying regionally. Although East Asia becomes wetter overall, diagnostic analyses indicate that neither the early nor the late Eocene climate supports a coherent, modern-style East Asian monsoon. Together, these results highlight the coupled roles of modified topography, collision-related land–sea reorganization, and atmospheric greenhouse gas reduction in shaping the Eocene Asian hydroclimate, and provide new constraints on the tectonic and climatic processes underlying the emergence of present-day dry–wet patterns.