Observed and Simulated Mesoscale Convective Systems over High Mountain Asia: 1. 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-km and 3-km resolution (the latter storm-resolving) to assess MCS characteristics and climate response over HMA. Part 1 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 2) and guiding future model development.