Réf. Duband 2003 - P

Référence bibliographique complète
DUBAND D. Extreme rainfall and flood events in autumn during 19th and 20th centuries in southern Europe basins influenced by mediterranean meteorological conditions. In: V.R.Thorndycraft, G. Benito, M. Barriendos and M.C. Llasat (2003). Palaeofloods, Historical Floods and Climatic Variability: Applications in Flood Risk Assessment (Proceedings of the PHEFRA Workshop, Barcelona, 16-19th October, 2002), p. 313-317.

Mots-clés
Flashfloods, discharge, extreme rainfall, southern Europe, trends.

Organismes / Contact
Division Eau et Environnement de la Société Hydrotechnique de France, Paris
d.duband@shf.asso.fr

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
Precipitation River discharge Floods Flashfloods

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Southern Europe Ebro - Rhone - Pô basins and the catchment areas along the coastal rivers of Spain, France and Italy       19th and 20th centuries

(1) - Modifications des paramètres atmosphériques
Reconstructions
 
Observations
Actually no significative trend has been detected in historical date (year, season, day) of rains and discharges hundred years old and more, in France, West Europe and other countries. But we can observe a succession of sequences of a process called the "Joseph effect" by B. Mandelbrot, of wet and dry years (20 to 50 years) without periodicities, perhaps due to North Atlantic oscillation (NAO).
Modélisations
 
Hypothèses
We can still consider the reasonable hypothesis for pseudo stationary distribution of extreme rainfalls and flood hazard, in reference to the last centuries, for the next twenty or forty future years. However, we remain aware of the opportunity that a global climate change can happen in the second part of the 21st century.

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 

(2) - Effets du changement climatique sur le milieu naturel
Reconstructions
 
Observations
Actually no significative trend has been detected in historical date (year, season, day) of rains and discharges hundred years old and more, in France, West Europe and other countries.
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

(3) - Effets du changement climatique sur l'aléa
Reconstructions
 
Observations
In the Ebro - Rhone - Pô basins and the catchment areas along the coastal rivers of Spain, France and Italy, affected by flashfloods, catastrophic events of flashfloods have happened very irregularly in the last centuries (succession of clusters and scarcities of floods), for example in the Cevennes region the number of observed flashfloods are 10 during the XVIII century, 26 during the XIX century and 14 during XX century.
Modélisations
 
Hypothèses
We can still consider the reasonable hypothesis for pseudo stationary distribution of extreme rainfalls and flood hazard, in reference to the last centuries, for the next twenty or forty future years.

Paramètres de l'aléa
Sensibilité du paramètre de l'aléa à des paramètres climatiques et du milieu
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 


The totality of the rainfalls does not find it's way around catchment areas, their global efficiency in producing the flood phenomena is frequently 5 to 30% and sometimes in extreme cases reaching 50 to 70%. The contribution of the rain depends on it's space/time distribution which can be reduced principally by infiltration in the soil according to the Horton process predominant in the Mediterranean, and at times mixed by the Beven process of contributing areas.

Certain meteorological circulation and configurations in the south of Europe and the West Mediterranean region create heavy rainfall events of different spatial scales (during several hours to a few days) at the origin of flashfloods in the EBRO - RHONE - PO basins and the catchment areas along the coastal rivers of Spain, France and Italy particularly during autumn (August, September, October and November).

(4) - Remarques générales
 

(5) - Préconisations et recomandations
Already in the present situation, communities have to learn to modify or adapt new life styles in regard to their activities and behaviour in the case of extreme floods. Of course, nothing can change unless clear and necessary information could be provided in the sense of optimising the prevention actions taken with the object of reducing the vulnerability on a medium term, and, developing modern and efficient organisation of alert and hydrometrological forecasting to improve the protection in a short term. In this scientific, technical, social, economical context, the collective memory of the historical is absolutely fundamental.

It is necessary to collect systematical observations from 1850 until 1950 on atmospheric pressure-air temperature, rainfall-discharge (height level) and on a daily basis with critical analysis of the data; from 1950 to 2000, the same collection and analysis can be made, completed by more detailed observations (hourly) and new parameters (radiosounding, satellites, radars....). Then it would be very important and useful to elaborate a database of this information concerning local and extensive rainfall-flood events, between 50 to 100 perhaps, available to all communities in Europe (scientific, historic, social, political, public...).

Applications will be:
- optimising prevention actions and improving rainfall and flood forecast,
- testing the hypothesis of climatic modification in regional /local extreme hydrological risks.

Références citées :

Goubet A. et al: Crues exceptionnels de l'année 1982 -1983 - Société Hydrotechnique de France (SHF) Paris 1988.

Lalanne Berdouticq G.: Aspects méthodologiques de la reconstitution des écoulements des grandes crues catastrophiques- Centre de Resugyes i d'estudis Catalanns-Colloque l'Aiguat del 1940, Vernet les Bains, October 1990 .

Llasat C., Barriendos M., Rigo T.: L'Analyse de la fréquence et de l'occurrence temporelle des fortes précipitations d'origine méditerranéenne causes des crues rares en Espagne et dans le Sud de la France, Colloque SHF Paris 2001, Variations climatiques et Hydrologie, La Houille Blanche n°6-7, 2002.

Llasat C, Ramis C, Barrantes J. : The Meteorology of High -Intensity Rainfall Events over the West Mediterranean Region, Remote Sensing reviews, 1996, Vol 14, pp 51-90.

Pardé M.: Les crues Italiennes catastrophiques de l'automne 1951 - La Houille Blanche, avril 1952 - SHF.

Visentini M., Pardé M.: Quelques données sur le régime du Pô - Annales de géographie XLV Année, Tome 45, Librairie Armand Colin 136, et Fonds Pardé, Institut de Géographie alpine, Grenoble - France.