Impact of orography on sub-daily precipitation upper tail from convection-permitting climate model simulations: a multi-model ensemble perspective

Understanding the impact of orography on the probability distribution of extreme precipitation at short (i.e., sub-daily) temporal scales, as well as on extreme-rainfall causative processes, is critical for managing risk from rainfall-triggered natural hazards in mountainous regions. High-resolution convection-permitting models (CPMs) are crucial for this type of analysis since they better represent convective processes key to short-duration extremes.

Here, we assess the ability of multi-model CPM ensemble CORDEX-FPS to represent the upper tail of sub-daily precipitation in a complex-orography region in the Eastern Italian Alps. In this area, different orographic impacts on sub-daily precipitation upper tail were reported at different event durations, and significant temporal trends in precipitation intensity were reported during the last few decades, making it a challenging and interesting test case for CPM simulations. An ensemble of six CPMs with a horizontal grid spacing of ∼2.2 km, driven by ERA-Interim reanalysis, are analysed and evaluated against ∼180 rain gauges. Since CPM simulations are too short (10 years) for analysing extremes using conventional methods, we use a non-asymptotic statistical approach (Simplified Metastatistical Extreme Value, SMEV), which was proven to provide reliable results even using short time records. We explore how the model spread vary with elevation and the ability of the multi-model mean to reproduce the distribution parameters and the extreme quantiles up to 100-year return period at different elevations.