Comprehensive Appraisal and Bias Diagnostics of CMIP6 HighResMIP Model Simulations on South Asian Summer Monsoon Precipitation

Abstract The South Asian summer monsoon (SASM) system, coupled with its intricate topography, presents formidable challenges to the accuracy of global climate models in realistically replicating the regional precipitation distribution. Employing atmospheric-only simulations from the High-Resolution Model Intercomparison Project (HighResMIP), this study rigorously assesses the capability of models with varying horizontal resolutions in simulating SASM precipitation, utilizing metrics such as horizontal configuration, intensity distribution, interannual variability, and long-term trends. The findings suggest that, despite intermodel discrepancies, high-resolution (HR) models exhibit substantial advantages over low-resolution (LR) models in simulating precipitation over complex orography, particularly in key regions such as the Himalayan foothills, the windward slopes of the Western Ghats, and the central–northern Indian plains. Nonetheless, limitations persist in accurately capturing the long-term trends of precipitation. A comprehensive appraisal reveals that the HR models CMCC-CM2-VHR4, EC-Earth3P-HR, ECMWF-IFS-HR, and HadGEM3-GC31-HM demonstrate superior aptitude in simulating the spatiotemporal distribution of precipitation. Analysis of the moisture budget equation reveals that atmospheric moisture variability in South Asia’s principal monsoon regions is primarily governed by the dynamical term dDY, which elucidates the origin of discrepancies in precipitation simulations between HR and LR models. Specifically, the HR model more precisely characterizes atmospheric circulation features and local dynamical processes and more realistically reproduces the activity characteristics of tropical cyclones over the Bay of Bengal. These improvements yield a more realistic dynamical environment for the SASM, thereby enhancing the accuracy and reliability of simulated precipitation distributions. Significance Statement Our findings reveal that high-resolution (HR) models significantly enhance monsoonal precipitation simulation over the complex terrain of South Asia, effectively reducing wet biases over the Tibetan Plateau and Pakistan regions. We find that CMCC-CM2-VHR4, EC-Earth3P-HR, ECMWF-IFS-HR, and HadGEM3-GC31-HM exhibit superior ability in resolving spatial patterns and interannual variability, resulting from their capacity to better capture atmospheric circulation, orographically driven vertical motions, and synoptic systems like tropical cyclones. These findings underscore the importance of increased model resolution for more reliable representations of monsoon dynamics and precipitation and highlight the need to prioritize HR models in future research.