Hydrometeorological analysis of the 29 August 2003 flash flood in the Eastern Italian Alps

The August 29, 2003, storm on the upper Tagliamento river basin in the eastern Italian Alps is examined as a prototype for organised convective systems that dominate the upper tail of the precipitation frequency distribution and are likely responsible for the majority of flash flood peaks in this area. The availability of high-resolution rainfall estimates from radar observations and raingauge networks, together with flood response observations derived from streamgauge data and post-event surveys, provides the opportunity to study the hydrometeorological and hydrological mechanisms associated with this extreme storm and the associated flood. The flood occurred at the end of a climatic anomaly of prolonged drought and warm conditions over Europe and the Mediterranean region. A characteristic of the event is its organization in well defined banded structures, some of which persisted in the same locations for the duration of the event. The steadiness of these rainbands led to highly variable precipitation accumulations and, associated with orographic enhancement, played a central role in the space-time organization of the storm. Two dominant controls on extreme flood response are recognised an analysed: steadiness of convective bands, and dry antecedent soil moisture conditions.