Documentation and analysis of the flood event in September 2024 in Lower Austria Phase 1: Event documentation

The flood event from September 12 to 20, 2024 was triggered by a Vb weather situation and led to extreme precipitation in Lower Austria, with over 400 mm of rain in five days in some places. This corresponds to more than 5.5 times the long-term average for September. The resulting extreme hydrological conditions caused exceptional flood peaks in several rivers with floods of over HQ100. Runoff volumes reached record levels and led to severe infrastructure damage, including the failure of flood protection dams and retention basins. The disaster claimed six lives in Austria and caused economic damage of over one billion euros (excluding ÖBB-related damage). Climate change is seen as a favorable factor for such extreme events. Forecasts point to an intensification of Vb weather conditions, with a seven percent increase in precipitation compared to pre-industrial times. A global temperature increase of two degrees Celsius could increase the precipitation of such events by at least another five percent. In addition, changes in land use and increasing land consumption exacerbate the risk of flooding and the potential for damage. In view of the unprecedented scale of this event, the BOKU University, Vienna was commissioned by the Lower Austrian provincial government to carry out a comprehensive documentation and analysis of the 2024 flood in a two-phase project. Phase 1 focuses on the compilation and synthesis of the event documentation from specialist offices, emergency organizations and authorities. Phase 2 comprises a detailed analysis of the event, the evaluation of the effectiveness of flood protection measures and cause-and-effect analyses. The results should help to improve flood risk management and increase resilience to future extreme events.