The September 2024 Danube flood compared to the 1899, 2002, and 2013 events: a hydrometeorological analysis in a changing climate

Abstract

Abstract. In September 2024, an exceptional flood occurred in the Austrian Danube Basin, producing the highest discharges in parts of Lower Austria since instrumental records began. This study analyses the meteorological and hydrological drivers of the 2024 event and compares them with three historic floods with return periods of around 100 years at the Austrian Danube – 1899, 2002, and 2013 – to identify similarities, differences, and emerging trends in flood generation. Using representative station observations, reanalysis data, and hydrometric records from a dense network of river gauges, we examine atmospheric circulation, spatio-temporal rainfall patterns, runoff response, and flood-wave propagation along the Danube and its tributaries. The 2024 flood was triggered by a quasi-stationary low-pressure system over the eastern Alps and western Hungary that produced two rainfall phases: a stratiform period in the west followed by convective extremes in the east, with local totals of 450–500 mm in five days. Although antecedent soil moisture was initially low, sustained rainfall led to rapid saturation and unusually high runoff coefficients (0.6–0.9) in central Lower Austria, where tributaries such as the Perschling and Kleine Tulln exceeded their HQ100 discharges by more than 150 %–250 %. In contrast, the main Danube and western Alpine tributaries showed only moderate responses. The comparison with historical floods reveals a gradual shift from Alpine-controlled, basin-wide events toward regionally concentrated, convectively enhanced floods. The 2024 case highlights the increasing importance of atmospheric persistence, antecedent saturation, and tributary synchronisation in shaping flood extremes, providing new insights for adaptive flood-risk management in a changing climate.