Orographic and land-sea contrast effects in convection-permitting simulations of extreme sub-daily precipitation

Abstract

Convection-permitting climate models (CPMs) represent a significant advancement compared to regional climate models, enabling more accurate simulations of extreme precipitation at fine spatial and temporal scales. Assessing the reliability of CPM projections for extreme short-duration precipitation requires understanding how well CPMs reproduce observed extremes—especially in Mediterranean regions, where such evaluations are rare. In this study, we assess the accuracy of simulations from a high-resolution CPM covering the entire Italy (VHR-PRO_IT), in reproducing sub-daily precipitation extremes. For this, we exploit observations from I²-RED, a comprehensive dataset of more than 5 000 quality-checked annual maximum time series from rain gauge observations. The comparison is performed by considering the median values of the annual maxima at 1, 3, 6, 12 and 24-h as a first step and rainfall quantiles up to 200-year return period as a second step. Our results show that model performance is influenced by both the distance from the coastline and elevation, highlighting an important role of orography and land-sea contrast in explaining CPM biases. Moreover, we find better performances when longer duration extremes are considered, while shorter durations are affected by strong underestimations, especially in coastal and low-elevation areas. These results hold significant implications for stakeholders and policymakers dealing with climate adaptation and flood risk management.