Observed and Simulated Mesoscale Convective Systems over High Mountain Asia. Part I: Model Evaluation

Mesoscale convective systems (MCSs) are key drivers of the hydrological cycle over High Mountain Asia (HMA), delivering essential warm-season rainfall but also triggering flash floods and landslides. Their simulation over this complex region remains challenging for coarse-resolution models, and regional convection-permitting models cannot fully capture large-scale feedback. In this two-part study, we use global models at 25-and 3-km resolution (the latter storm resolving) to assess MCS characteristics and climate response over HMA. Part I provides a comprehensive evaluation against satellite observations. Both models capture the spatial distribution and seasonality of MCSs but overestimate warm-season frequency, with underestimation at low elevations and overestimation at high elevations. The storm-resolving model better reproduces the diurnal cycle. At the event scale, simulated MCSs are slightly larger, longer lived, and more intense than observed. Both reproduce the dominant eastward propagation and speeds but exaggerate a secondary southwestward mode. They capture broad precipitation patterns, including the dry zone north of the Himalayas, though the 25-km model retains a wet bias along the southern slopes that is reduced in the 3-km simulation. These findings highlight both the promise and limitations of current high-resolution global models in representing MCSs over complex terrain, providing a basis for assessing historical and future changes (Part II) and guiding future model development. SIGNIFICANCE STATEMENT: Mesoscale convective systems (MCSs) are organized clusters of deep convection that play a key role in regulating the energy and water cycles over High Mountain Asia (HMA). They often produce hazardous weather, including flooding, strong winds, and hail. Accurately simulating and projecting these systems are essential for improving predictions of both mean climate conditions and extreme events. Because MCSs have fine-scale structures and complex interactions with large-scale circulation, high-resolution global models have become valuable tools for studying them. In this study, we conduct a detailed evaluation of a high-resolution global climate model and a global storm-resolving model in simulating key characteristics of MCSs over HMA. These evaluations provide the foundation for subsequent analyses of historical trends and future projections of MCS activity in the region.