Flash floods in Catalonia: a recurrent situation

Abstract

Abstract. This work focuses on the analysis and characterization of the flash flood events occurring during summer in Catalonia. To this aim, a database with information about the social impact produced by all flood events recorded in Catalonia between 1982 and 2007 has been built. The social impact was obtained systematically on the basis of news press data and, occasionally, on the basis of insurance data. Flood events have been classified into ordinary, extraordinary and catastrophic floods, following the proposal of Llasat et al. (2005). However, bearing in mind flash flood effects, some new categories concerning casualties and car damage have also been introduced. The spatial and temporal distribution of these flood events has been analyzed and, in an effort to better estimate the social impact and vulnerability, some indicators have been defined and analyzed for a specific region. These indicators allow an analysis of spacial and temporal trends as well as characterization of the events. Results show a flash-flood increase in summer and early autumn, mainly due to inter-annual and intra-annual changes in population density.

Tornadoes and waterspouts in Catalonia (1950–2009)

“…However, a comparison with precipitation and flash floods evolution in the studied region underlines the potential large impact of the societal factors in the observed increase. It is noteworthy that no trend in heavy rainfall distribution has been detected, despite a positive trend in flash flood frequency (Llasat et al, 2010).…”

“…This concentration in late summer and autumn has also been observed in Italy (Giaiotti et al, 2007) and Portugal (Leitão, 2003), in contrast to a spring frequency maximum in United States and other European countries such as France (Paul, 2001), Germany (Dotzek, 2001) or Ireland (Tyrrell, 2003). This seasonal concentration is most likely due to the inertia of sea surface temperature in the Mediterranean, in conjunction with the changes in the latitude of strong westerlies and the track of travelling synopticscale cyclones, and coincides strongly with the seasonal flash-floods distribution in the region (Llasat et al, 2010).…”

Mediterranean-climate streams and rivers: geographically separated but ecologically comparable freshwater systems

“…During the wet period, precipitation restores 368 longitudinal, lateral-and vertical-flow connectivity; disconnected pools disappear, and 369 the river functions again as a sequence of pools connected to riffles. In small and steep 370 basins, this flow expansion occurs with a very short time lag because precipitation 371 usually falls as intense storms that often lead to intense flash-floods from late-summer 372 to autumn (Camarasa-Belmonte & Segura-Beltrán, 2001; Llasat et al, 2010). During 373 the dry period, the lack of precipitation and the high evapotranspiration rate of med-374 rivers result in a steadily reduction of the longitudinal-, lateral-, and vertical-flow 375 (Bonada et al, 2007b) and lead to a sequence of disconnected pools that may ultimately 377 lack any surface water, leaving dry riverbeds.…”

Governing for Integrated Water and Flood Risk Management: Comparing Top-Down and Bottom-Up Approaches in Spain and California

“…These coastal Catalan and San Francisco Bay regions lend themselves well to comparison by virtue of their similar sizes and populations, similar topography, climate, and consequent nature of the flood hazards, and history of water resources development. Furthermore, the highly variable hydrological regime that characterizes Mediterranean climate-rivers [6] and the rapid urbanization in recent decades along the coast in both regions give these areas among the highest flood risk in Europe and North America [30][31][32]. The steady increase in catastrophic flood losses in Catalonia is evidently due not to an increase in rain intensities or amounts, but rather is related to increased human occupation of flood prone areas [33].…”