Future changes in sub-daily catchment scale extreme precipitation in the Great Alpine Region

Understanding the scale-dependent behavior of extreme precipitation in mountainous basins is critical for improving effective adaptation strategies to rising flood risks. This study investigates the future changes in sub-daily catchment scale extreme precipitation across the Great Alpine Region. In particular, we examine how information about the projected changes of sub-daily point design precipitation can be transferred to projected changes of catchment-scale precipitation with the same return period.

Projections are derived from a 9-member ensemble of convection-permitting climate models (CPMs) provided by the CORDEX-FPS Convection project. The dataset spans historical (1990–1999) and far-future (2090–2099) periods under the high-emissions scenario (RCP8.5), with precipitation outputs remapped to a 3 km spatial resolution and a 1-hour temporal resolution. To analyze extremes, we apply the Simplified Metastatistical Extreme Value (SMEV) framework, a robust non-asymptotic statistical method well-suited for short data records.

The spatial analysis focuses on mean areal precipitation extremes, computed over various moving average window sizes, with the largest block encompassing an area of approximately 4000 km² (21 × 21 grid cells). Changes in 3-km grid design precipitation are translated to catchment-scale design events by quantifying changes in Areal Reduction Factor (ARF). We calculate the Areal Reduction Factor (ARF) for the window sizes across different durations and return periods, enabling us to quantify the scaling relationships between 3 km grid and areal precipitation extremes. By examining the dependence of ARF on duration and return periods under future climate conditions, we identify potential shifts in the spatial structure and intensity of extreme precipitation events. Our study underscores the importance of using high-resolution ensemble modeling to capture the complex interplay between spatial variability and extreme precipitation, and contributes to addressing the challenges posed by changing precipitation extremes in mountainous regions.