Assessment of variability and trends of heavy precipitation in Trentino – South Tyrol (north-eastern Italian Alps) based on rain-gauge records (1956-2020)

In recent decades, the Alpine regions have been affected by several heavy precipitation events occasionally associated with storms causing landslides, debris flows, forest damage or flooding with cascading impacts to socio-economic systems. There is scientific evidence that a warming climate is likely to induce changes in the intensity and occurrence of precipitation extremes, even though extracting a long-term changing signal on regional and local scale is still challenging and requires an adequate observation coverage.

Some studies on extreme precipitation observed in the Alpine region exist, but only a few focus more in detail on the Trentino-Alto Adige area (north-eastern Italian Alps). In this context, the intensity and frequency of heavy precipitation, their spatial variability and trends over 1956-2020 are analysed for the region based on an archive of quality-checked daily historical records from more than 60 rain gauges.

The annual and seasonal analyses of maxima and exceedances of the 97^th percentile show distinctive spatial patterns in both magnitude and seasonality. Maxima primarily occur during summer in the northern and more alpine part of the region, and during autumn in the south where the influence of the Mediterranean climate is more pronounced. Almost two thirds of the analysed stations reveal an increasing tendency in either the intensity or the frequency of heavy precipitation, especially in the north, even though trends are statistically significant only for a limited number of stations (e.g. less than 10% for annual maxima). The 1956-2020 intense precipitation observations are also scaled with global and regional temperatures and results are compared with previous studies in surrounding countries in order to assess global and regional warming effects on extreme changes. Finally, the extreme value distributions based on the 65-year records and two subsequent subperiods (1961-1990 and 1991-2020) provide a first evaluation of changes in statistical properties and precipitation amounts associated to different return periods. This is also used to characterize the local precipitation intensities during the exceptional event which hit north-eastern Alps in 2018, named storm Vaia, with intense precipitation together with extreme wind speed conditions.

This contribution shows and discusses the main results and provides an outlook towards the assessment of climate drivers of precipitation events in the region, the occurrence of compound extremes and links to subsequent impacts.

The research leading to these results has received funding from Interreg Alpine Space Program 2021-27 under the project number ASP0100101, “How to adapt to changing weather eXtremes and associated compound and cascading RISKs in the context of Climate Change” (X-RISK-CC).