Controls on the temporal evolution of extreme precipitation in Austria

The temporal evolution of extreme precipitation is expected to be influenced by the broader impacts of climate change. This is generally considered to be due to the increased water-holding capacity of a warmer atmosphere, as well as alterations in atmospheric circulation patterns. However, gaining a comprehensive understanding of how extreme precipitation has changed in the past has been a challenge due to limited historical data and inherent uncertainties, particularly when examining short-duration rainfall events such as those occurring within a one-hour period.

By analyzing rainfall gauge data from Austria collected during the twentieth century, we observe significant decadal-scale variations in daily extreme precipitation. These variations suggest that the frequency and intensity of daily extreme events are highly variable over time. In contrast, our analysis of hourly extreme precipitation reveals a more consistent and noticeable upward trend over the past four decades. This trend corresponds with the increase in global temperatures, showing a 7% rise in hourly extreme precipitation for every 1°C of warming, which is in line with the Clausius-Clapeyron relationship. This increase in hourly extreme precipitation is consistent across both the northern and southern regions of the Alps, indicating that the effects of warming are widespread across Austria. On the other hand, daily extreme precipitation appears to be more strongly influenced by atmospheric circulation patterns, with a more notable correlation to decadal-scale variations in these patterns. These atmospheric circulation shifts are responsible for driving the weather systems that generate extreme precipitation events, particularly on the daily timescale.

In summary, our findings suggest that thermodynamic changes, such as the increase in temperature, have a more pronounced impact on hourly extreme precipitation than on daily extremes. This highlights the distinct processes at play for different timescales, where the short-term (hourly) extreme events are more closely tied to the fundamental thermodynamic properties of the atmosphere, while longer-term (daily) extremes are influenced more by large-scale atmospheric circulation dynamics.