Estimation of extreme flash flood evolution in Barcelona County from 1351 to 2005

Abstract

Abstract. Every year, flash floods cause economic losses and major problems for undertaking daily activity in the Catalonia region (NE Spain). Sometimes catastrophic damage and casualties occur. When a long term analysis of floods is undertaken, a question arises regarding the changing role of the vulnerability and the hazard in risk evolution. This paper sets out to give some information to deal with this question, on the basis of analysis of all the floods that have occurred in Barcelona county (Catalonia) since the 14th century, as well as the flooded area, urban evolution, impacts and the weather conditions for any of most severe events. With this objective, the identification and classification of historical floods, and characterisation of flash-floods among these, have been undertaken. Besides this, the main meteorological factors associated with recent flash floods in this city and neighbouring regions are well-known. On the other hand, the identification of rainfall trends that could explain the historical evolution of flood hazard occurrence in this city has been analysed. Finally, identification of the influence of urban development on the vulnerability to floods has been carried out. Barcelona city has been selected thanks to its long continuous data series (daily rainfall data series, since 1854; one of the longest rainfall rate series of Europe, since 1921) and for the accurate historical archive information that is available (since the Roman Empire for the urban evolution). The evolution of flood occurrence shows the existence of oscillations in the earlier and later modern-age periods that can be attributed to climatic variability, evolution of the perception threshold and changes in vulnerability. A great increase of vulnerability can be assumed for the period 1850-1900. The analysis of the time evolution for the Barcelona rainfall series shows that no trend exists, although, due to changes in urban planning, flash-floods impact has altered over this time. The number of catastrophic flash floods has diminished, although the extraordinary ones have increased.

Flash-floods in Catalonia: the social perception in a context of changing vulnerability

“…The rise in the number of extraordinary floods is particularly noticeable in the coast and began already in the 19th century. In the case of the city of Barcelona, although this increase in the number of extraordinary floods is also detected, the number of catas-70 M. C. Llasat et al: Flash-floods in Catalonia trophic floods has decreased thanks to the drainage system of the city (Barrera et al, 2006). The evolution of annual maximum daily precipitation in Barcelona from 1854 to 2005 does not show any significant trend.…”

“…This last scale can be also applied to recent events, in order to build up a common series starting some centuries ago and ending nowadays (Barrera et al, 2006) 2.2 The selected FLASH events…”

Study of the precipitation evolution in Catalonia using a mesoscale model (1971–2000)

“…The number of days with daily precipitation above 50 mm has been chosen as the variable to make the comparison with floods. This is a daily precipitation threshold related to floods in the studied area, since no flood was recorded in days with less than 50 mm in the last 150 years in Barcelona city (Barrera et al, 2006). Figure 4 shows a good coincidence between observed (flood evolution) and simulated (extreme precipitation events) values.…”

The role of different factors related to social impact of heavy rain events: considerations about the intensity thresholds in densely populated areas

“…For the city of Barcelona, an increase in the number of extraordinary floods was detected, particularly since the 19th century, due to rising vulnerability (Llasat et al, 2008), but on the other hand the number of catastrophic floods has decreased thanks to the renewal of the drainage system of the city (Barrera et al, 2006). Consequently, it is important to select a period with no significant changes in vulnerability in order to reduce it to the point of being negligible.…”