Trends in flash flood events versus convective precipitation in the Mediterranean region: The case of Catalonia

Maria Carmen Llasat, Raul Marcos, Marco Turco, Joan Gilabert, Montserrat Llasat-Botija

ABSTRACT

The aim of this paper is to analyse the potential relationship between flash flood events and convective precipitation in Catalonia, as well as any related trends. The paper starts with an overview of flash floods and their trends in the Mediterranean region, along with their associated factors, followed by the definition of, identification of, and trends in convective precipitation. After this introduction the paper focuses on the north-eastern Iberian Peninsula, for which there is a long-term precipitation series (since 1928) of 1-min precipitation from the Fabra Observatory, as well as a shorter (1996–2011) but more extensive precipitation series (43 rain gauges) of 5-min precipitation. Both series have been used to characterise the degree of convective contribution to rainfall, introducing the β parameter as the ratio between convective precipitation versus total precipitation in any period. Information about flood events was obtained from the INUNGAMA database (a flood database created by the GAMA team), with the aim of finding any potential links to convective precipitation. These flood data were gathered using information on damage where flood is treated as a multifactorial risk, and where any trend or anomaly might have been caused by one or more factors affecting hazard, vulnerability or exposure. Trend analysis has shown an increase in flash flood events. The fact that no trends were detected in terms of extreme values of precipitation on a daily scale, nor on the associated ETCCDI (Expert Team on Climate Change Detection and Indices) extreme index, could point to an increase in vulnerability, an increase in exposure, or changes in land use. However, the summer increase in convective precipitation was concentrated in less torrential events, which could partially explain this positive trend in flash flood events. The β parameter has been also used to characterise the type of flood event according to the features of the precipitation. The highest values correspond to short and local events, usually with daily β values above 0.5, while the minimum threshold of daily β for catastrophic flash floods is 0.31

Keywords

  • Flash floods;
  • Convective precipitation;
  • β parameter;
  • Trend analysis;
  • Mediterranean

You can download here: http://www.sciencedirect.com/science/article/pii/S0022169416303079

Anuncios

Testing instrumental and downscaled reanalysis time series for temperature trends in NE of Spain in the last century

M. Turco, R. Marcos, P. Quintana-Seguí, M. C. Llasat

Abstract

In the context of climatic temperature studies, more often than not a time series is affected by artificial inhomogeneities. To overcome such limitation, we propose a new simple methodology in which promising results point not only toward the detection of unknown inhomogeneous periods but also toward the possibility of reconstructing the uncertain portion of the series. It is based on a parsimonious statistical downscaling (Multiple Linear Regression) of the large-scale 20CR reanalysis data. This method is successfully applied upon two long-range temperature series from a couple of centennial observatories (Ebre and Fabra, NE of Spain) which do not have nearby suitable temperature series to compare with. Results of trend analysis point to a clear signal of warming, with a larger rate of increase for the maximum temperature (respect to the minimum one), for the more recent decades (respect to the whole available period), and for the original series (respect to the reconstructed ones).

Article: http://link.springer.com/article/10.1007%2Fs10113-012-0363-9

Flash flood evolution in North-Western Mediterranean

Abstract

The present paper shows an in-depth analysis of the evolution of floods and precipitation in Catalonia for the period 1981–2010. In order to have homogeneous information, and having in mind that not gauge data was available for all the events, neither for all the rivers and stream flows, daily press from a specific newspaper has been systematically analysed for this period. Furthermore a comparison with a longer period starting in 1900 has been done. 219 flood events (mainly flash flood events) have been identified for the period of 30 years (375 starting in 1900), 79 of them were ordinary, 117 of them were extraordinary and 23 of them were catastrophic, being autumn and summer the seasons with the maxima values. 19% of the events caused a total of 110 casualties. 60% of them died when they tried to cross the street or the stream. Factors like the evolution of precipitation, population density and other socio-economical aspects have been considered. The trend analysis shows an increase of 1 flood/decade that probably has been mainly due to inter-annual and intra-annual changes in population density and in land-use and land-cover.

Authors: Maria Carmen Llasat, Raül Marcos, Montserrat Llasat-Botijaa, Joan Gilabert, Marco Turco i Pere Quintana-Seguí.

Podéis descargar el artículo de forma gratuita hasta el 31 de agosto. LINK:  http://authors.elsevier.com/a/1PLdgcd3RmlUW

The snow storm of 8 March 2010 in Catalonia (Spain): a paradigmatic wet-snow event with a high societal impact

Authors.  M. C. Llasat, M. Turco, P. Quintana-Seguí and M. Llasat-Botija

Abstract. 

A heavy precipitation event swept over Catalonia (NE Spain) on 8 March 2010, with a total amount that exceeded 100 mm locally and snowfall of more than 60 cm near the coast. Unusual for this region and at this time of the year, this snowfall event affected mainly the coastal region and was accompanied by thunderstorms and strong wind gusts in some areas. Most of the damage was due to “wet snow”, a kind of snow that favours accretion on power lines and causes line-breaking and subsequent interruption of the electricity supply. This paper conducts an interdisciplinary analysis of the event to show its great societal impact and the role played by the recently developed social networks (it has been called the first “Snowfall 2.0”), as well to analyse the meteorological factors associated with the major damage, and to propose an indicator that could summarise them. With this aim, the paper introduces the event and its societal impact and compares it with other important snowfalls that have affected the Catalan coast, using the PRESSGAMA database. The second part of the paper shows the event’s main meteorological features and analyses the near-surface atmospheric variables responsible for the major damage through the application of the SAFRAN (Système d’analyse fournissant des renseignements atmosphériques à la neige) mesoscale analysis, which, together with the proposed “wind, wet-snow index” (WWSI), allows to estimate the severity of the event. This snow storm provides further evidence of our vulnerability to natural hazards and highlights the importance of a multidisciplinary approach in analysing societal impact and the meteorological factors responsible for this kind of event.

Full article HERE.

 

Lectura de Tesis Doctoral de Marco Turco (membre del grup GAMA i del CMCC)

Aquest 25 de juliol a les 11 del matí, Marco Turco investigador del grup GAMA i del CMCC llegirà la Tesis Doctoral que ha estat dirigida per la Dra. María Carme Llasat.