Orographic impact on extreme sub-daily precipitation is critical for
risk management but remains insufficiently understood due to complicated
atmosphere-orography interactions and large uncertainties. We
investigate the problem adopting a framework able to reduce
uncertainties and isolate the systematic interaction of Mediterranean
cyclones with a regular orographic barrier. The average decrease with
elevation reported for hourly extremes is found enhanced at sub-hourly
durations. Tail heaviness of 10-minute intensities is negligibly
affected by orography, suggesting self-similarity of the distributions
at the convective scale. Orography decreases the tail heaviness at
longer durations, with a maximum impact around hourly scales. These
observations are explained by an orographically-induced redistribution
of precipitation towards stratiform-like processes, and by the
succession of convective cores in multi-hour extremes. Our results imply
a breaking of scale-invariance at sub-hourly durations, with important
implications for natural hazards management in mountainous areas.