Integrated post-event survey of the record-breaking Central Italy flash flood of September 2022: observation strategy and lessons learned

<p>Spatial and temporal scales of occurrence of flash floods, combined with the space and time scales of conventional measurement networks of rain and discharge, make these events particularly difficult to observe. The effective documentation of flash floods requires therefore post-flood survey strategies encompassing accurate radar rainfall estimation, indirect reconstruction of peak discharges, field observations of the geomorphic processes and large wood dynamics associated. This also provides ground for quantifying, analyzing and interpreting impacts on communities, infrastructures and ecosystems.</p> <p>This work describes the methods applied and the early results achieved with the survey of the exceptional flash flood that hit the Marche region (Central Italy) between the 15th and 16th of September 2022, with rainfall reaching cumulated local peaks exceeding 400mm and recurrence interval exceeding 500 years for certain rainfall durations. The flood occurred at the end of a climatic anomaly of prolonged drought and warm conditions over Europe and the Mediterranean region, and caused 12 fatalities and severe damages to activities and buildings.</p> <p>The documentation of the flash flood reveals high peak flood discharges and a complex flood response. Peak discharges were estimated at 12 cross sections in the upstream sector of the affected river basin, with drainage areas ranging from 4 to 120 km2 and specific flood peaks exceeding 20 m3/(s km2).</p> <p>Among the lessons learned from the field study of this flash flood we underline: i) the need to properly represent the drought history to describe the actual antecedent soil moisture status, ii) the highly variable interaction of flood flows with floating large wood elements trapped at bridges, iii) the need of integrating the documentation of both hazard, impacts and vulnerability aspects to advance models for more effective flood risk management.</p>