Impact of orography on current and future extreme sub-daily precipitation

Major natural hazards in mountainous regions, such as flash floods and debris flows are mainly triggered by short-duration extreme precipitation. A better understanding of how these events are affected by orography can significantly improve risk management and adaptation to changing climate. Recently, significant progress has been made in high-resolution (particularly convection-permitting) modelling of precipitation over complex terrain, with the advantages of improved topographical features, physical representation of mountain-precipitation interactions, and avoided errors from convective parameterizations.

Here, we examine the mountain-precipitation interactions for subdaily precipitation extremes from three 10-year time slices (historical 1996-2005, near-future 2041-2050, and far future 2090-2099 – under the RCP8.5 scenario) of COSMO-crCLIM model simulations at 2.2 km resolution. We use the Upper Adige river basin in the Eastern Italian Alps, with a good coverage of high-quality precipitation data, as a case study. The ability of the convection-permitting model to represent the orographic impact on precipitation is examined based on a comparison between 2000-2009 simulations from the COSMO model run driven with ERA Interim, and observations from the local rain gauge network.

Given the availability of relatively short time-slices of model simulation, which prevent the use of conventional extreme value methods, we use here methods based on the concept of ordinary events, which are all the independent events that share the statistical properties of extremes. This offers now an opportunity for deriving frequency analyses from shorter data records, promising improved applications based on convection precipitation simulations.