Hydrometeorological Analysis of the 29 August 2003 Flash Flood in the Eastern Italian Alps

Abstract

The 29 August 2003 storm on the upper Tagliamento River basin in the eastern Italian Alps is examined as a prototype for organized 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 rain gauge networks, together with flood response observations derived from stream gauge 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 recognized and analyzed: steadiness of convective bands and dry antecedent soil moisture conditions.

Improvement of resilience of urban areas by integrating social perception in flash-flood risk management

“…The resulting floods have a rapid hydrological response, characterized by ''peaky'' hydrographs (i.e., short lag time). The flow peaks are reached within a few hours, thus giving little or no advance warning to mitigate flood damage (Borga et al, 2007;Borga et al, 2008). This hydrological response leads to the occurrence of a typology of floods known as flash floods because of their rapid onset, i.e., within six hours of rainfall (Ogden et al, 2000;Delrieu et al, 2005;Marchi et al, 2010;Hapuarachchi et al, 2011;Naulin et al, 2013;Ballesteros-Canovas et al, 2015).…”

Assessing debris flow activity in a changing climate

“…Both have daily precipitation records covering 1950-2009, and were exposed to numerous documented debris flows (Barcelonnette: 99 over 66 days, Fella River: 335 over 24 days). The areas are known to have high intensity rainfall as primary trigger for debris flows, allowing for similar meteorological proxies to be used in both areas (Borga et al 2007;Remaitre and Malet 2010). Sub-daily rainfall, although often a precursor for debris flows, was not considered due to the short available records and because daily rainfall totals are considered more reliably reproduced in climate models (Maraun et al 2010).…”

“…The Fella River catchment regularly experiences debris flows and flash floods due to heavy precipitation from synoptic features as well as mesoscale convection (Borga et al 2007). During winter, precipitation is derived primarily from synoptic features such as lows and fronts, varying significantly from year to year (Ceschia et al 1991).…”

“…During winter, precipitation is derived primarily from synoptic features such as lows and fronts, varying significantly from year to year (Ceschia et al 1991). In the summer months, convective processes become more important for rainfall generation, with local daily totals exceeding 400 mm (Borga et al 2007). The most recent catastrophic event was in August 2003, when more than 400 mm of rainfall was recorded, triggering more than 100 debris flows.…”

Comment on ‘The influence of geological–morphological and land-use settings on shallow landslides in the Pogliaschina T. basin (northern Apennines, Italy)’ by Bartelletti et al. (2017)

“…Such narrow elongated bands, which enhance the spatial variability of flood response and associated landsliding, are often observed in mesoscale convective systems (e.g. Borga, Boscolo, Zanon, & Sangati, 2007;Fuhrmann, Konrad, & Band, 2008). In the Pogliaschina basin, a striking difference between the rainfall distribution presented in Figure 3 of Bartelletti et al (2017) and that of Figure 1 is the rainfall amount in the southernmost sector of the basin.…”