Improved Performance of High‐Resolution Climate Models in Simulating Asian Monsoon Rainfall Extremes

Rainfall extremes are one of the most difficult features to simulate using global climate models. Using pairs of high‐ and low‐resolution atmosphere‐only simulations from the High‐Resolution Model Intercomparison Project, we assess whether and how the horizontal grid spacing influences model's skill in simulating the Asian summer monsoon rainfall extremes. Despite the large inter‐model spread, improved model performance is seen across most models as resolution increases, both in terms of spatial distribution and intensity of monsoon rainfall extremes. Rainfall extremes are enhanced at the windward side of steep topography such as the foothills of Himalayas, and in the heavy monsoon regions such as central India, southern China, and western North Pacific. The improvements are found to be associated with a better representation of the vertical ascents and models' ability in simulating the rain‐producing synoptic low‐pressure systems, which are more frequent and stronger at higher resolutions. Plain Language Summary Adequate simulations of rainfall extremes are essential for climate models to be useful for assessing regional climate impacts. However, notable biases exist in climate model simulations of Asian monsoon rainfall extremes and their spatial distributions. In the current work, we find that models with finer horizontal resolutions (smaller grid spacing) correct substantially the dry biases that are common in coarse resolution model simulations. The improvement is mainly through better simulations of rainfall extremes along the windward side of the steep topography such as the foothills of Himalayas, and over heavy monsoon regions including central India, southern China, the East Asian shorelines, and western North Pacific. Further analysis indicates that the enhanced extreme rainfall in high‐resolution models is associated with intensified vertical ascents during the occurrence of rainfall events and is attributable to more frequent and stronger monsoon low‐pressure systems, which are among the most important heavy rain‐bearing meteorological systems in the Asian summer monsoon regions. Key Points Finer resolution models reduce dry biases in modeled Asian monsoon rainfall extremes Improved simulation of monsoon rainfall extremes attributed to better representation of monsoon low‐pressure systems (LPSs) Higher resolution models tend to produce more frequent and stronger LPSs