Future alpine precipitation extremes under high-impact atmospheric circulation patterns

Understanding the behaviour of future extreme precipitation in the European Alps is a major adaptation challenge, as these events often cause flooding and severe impacts on infrastructure and society. Convection-permitting models (CPMs) have recently emerged as a key tool to better represent extreme precipitation processes in complex Alpine terrain, overcoming limitations of regional climate models (RCMs). While previous studies have analysed future changes in hourly and daily precipitation extremes using CPMs, it remains unclear how extremes will evolve under known impactful atmospheric circulation patterns, such as deep Mediterranean cyclones or persistent southerly flow regimes associated with major Alpine flood events.

Here, we investigate future precipitation changes conditioned on circulation types associated with observed high-impact events. We build on 6 impactful historical circulation types derived from the circulation classification scheme proposed in Lemus-Canovas et al. (2025). To identify circulation and   precipitation patterns analogous to these target circulation types, we apply a combined circulation–precipitation analogue framework. Candidate days are required to belong to the 10% closest circulation analogues, defined by the joint similarity of daily sea-level pressure and 500 hPa geopotential height fields simulated by each of the five EURO-CORDEX RCMs relative to the corresponding ERA5 circulation-type composite, quantified using a root-mean-square distance over the European domain. In addition, these candidate days must exhibit high precipitation-pattern agreement, defined as correlations exceeding the 90th percentile between CPM-simulated daily precipitation and an Alpine-wide observational precipitation dataset. Note that CPM outputs are first aggregated from hourly to daily resolution for the purpose of analogue selection. The final analogue dates are retained when basin-averaged precipitation exceeds the 90th percentile—computed separately for each experiment (Historical: 1996–2005; RCP8.5: 2090–2099) and weather type—if either 1-hour or 24-hour accumulated precipitation exceed the threshold in the most affected Alpine basins.

Our results show a precipitation intensification of autumn Mediterranean-origin weather types across all accumulation steps by the end of the century. For these circulation types, hourly precipitation extremes in CPMs scale with temperature   at or above the Clausius–Clapeyron rate (~7%/K), while weaker scaling is found at daily timescales. In contrast, summer-dominated weather types exhibit slight intensity increases at hourly scales but decreases at daily accumulations. These findings highlight strong circulation-dependent and scale-dependent changes in Alpine precipitation extremes and are particularly relevant for future risk management in the Alps.

References:

Marc Lemus-Canovas, Manuela Irene Brunner, Massimiliano Pittore, et al. Spatio-temporal patterns and drivers of high-impact precipitation events in the European Alps (1961-2022). ESS Open Archive . September 12, 2025. https://doi.org/10.22541/essoar.175767109.93227583/v1