Precipitation Trends over southern High Mountain Asia affected by Indian Ocean warming: Insights from high- and low-resolution versions of CMIP6 models

Summer precipitation over High Mountain Asia (HMA) has exhibited a dipolar trend over the past 50 years. Understanding its future changes and underlying mechanisms relies heavily on climate models. However, the impact and mechanisms of model resolution on the simulation of long-term precipitation trends over the HMA remain underexplored. In this study, we use six pairs of models with high- and low-resolution comparisons from the CMIP6 all-forcing experiments to investigate the resolution-dependent differences in the long-term trends of summer precipitation from 1951 to 2024. The results show that compared to low-resolution models, the simulations from high-resolution models are closer to observations, with the largest improvement in the southern margin of the HMA and surrounding areas (STP), where the wet bias is reduced by approximately 65%.  The moisture budget, moist static energy budget, and mixed-layer heat budget are used to explore the mechanism behind this reduction in wet bias. High-resolution models, with their enhanced ability to simulate oceanic advection and mixing, can capture the central-warm and eastern-cool tropical Indian Ocean SST pattern better. This SST pattern suppresses precipitation over Malaysia and the South China Sea, triggering Rossby waves that generate an anomalous anticyclone over the northern Bay of Bengal. The anticyclone then transports dry air to the STP, suppressing local convection and reducing wet bias. Our study emphasizes the importance of simulating Indian Ocean warming for accurately representing long-term precipitation trends over HMA.