Brief communication: How extreme was the thunderstorm rain in Vienna on 17 August 2024? A temporal and spatial analysis

Abstract. On 17 August 2024, a single thunderstorm cell over Vienna, Austria, produced 107 mm of rainfall within two hours at the “Hohe Warte” weather station, which has recorded hourly precipitation since 1941 – one of the world's longest-running sub-daily precipitation time series. This amount, with an estimated return period of approximately 700 years, is nearly twice as large as the second-largest event on record in the greater Vienna area. Comparing rain gauge data with a radar-based gridded dataset, we found that multiple events were missed by the station network. 100-year return periods of two-hour precipitation were 63 to 77 mm for rain gauge data and 61 to 90 mm for the radar-based data, underscoring the extremity of the 2024 event. Although the extreme precipitation time series shows no significant statistical trend, conditioning the return period on average mid-tropospheric temperature reduces the return period from 700 to 300 years, suggesting that climate change increases the frequency of such events.