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

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PhD position at ENIT (Tarbes) and IMFT (Toulouse): Impact model for the evaluation of the flooding risk.

Context and objectives:

The term “flash flood” refers to sudden floods having high peak discharges in a short response time. They result from a combination of meteorological and hydrological factors. Intense storm events delivering high amounts of rain water appear to be the first condition for flash flooding to be initiated. Watershed characteristics such as small catchments (under 500 km2 ) or steep slopes are associated with short and rapid flood timing. Flash floods are one of the most destructive hazards in the Mediterranean region and have caused casualties and billions of euros of damages in France over the last two decades. The recent case of June 2013 occurred in the Pyrenees killed 2 people and resulted in thousands of victims. The damages were estimated at about 134 million euros. The contrasted topography, the complexity of the continental surfaces in terms of geology and land use, the difficulty to characterize the initial moisture state of the catchments make these extreme events very difficult to assess and predict. The proposed PhD will aim at improving the understanding of the hydrological response by contemporary use of empirical and analytical (or rainfall-runoff) modelling. The ambition is to develop an operational methodology for the anticipation of the risk of inundation. The work will include an inter-comparison of models dedicated to flash flood prediction and allowing the characterization of the resulting risk. The proposed work will therefore contribute to the building of a relevant methodology of risk evaluation for a better protection of the population. The long-standing collaboration between the IMFT and the SCHAPI2 will facilitate the transfer of knowledge to the appropriate operational services. Leer más de esta entrada

9th HyMeX Workshop 21-25 September 2015, Mykonos, Greece

General information

The 9th HyMeX workshop will take place from 21 to 25 September 2015, in Mykonos Island, Greece. It will be organized by the National Observatory of Athens at Saint-John hotel.

Objectives

The general objectives of the HyMeX workshops are to strengthen the links and knowledge exchange, as well as to foster collaborations within the HyMeX research community. The 9th HyMeX workshop will occur at midterm of the programme. It will be the opportunity to assess the achievements of the programme, both in terms of data collected and science results, against the original objectives of the HyMeX Science Plan (http://www.hymex.org/public/documents/HyMeX_Science_Plan.pdf). Running over 5 days, the programme will consist of plenary sessions with review solicited talks and Science Teams oral and poster sessions with an open call for contributions to present and discuss recent scientific progresses regarding the Mediterranean water cycle. Leer más de esta entrada

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

Effect of radar rainfall time resolution on the predictive capability of a distributed hydrologic model

Atencia, A., L. Mediero, M. C. Llasat, and L. Garrote, 2011.

Abstract.

The performance of a hydrologic model depends on the rainfall input data, both spatially and temporally. As the spatial distribution of rainfall exerts a great influence on both runoff volumes and peak flows, the use of a distributed hydrologic model can improve the results in the case of convective rainfall in a basin where the storm area is smaller than the basin area. The aim of this study was to perform a sensitivity analysis of the rainfall time resolution on the results of a distributed hydrologic model in a flash-flood prone basin.

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Using Lightning Data to Better Understand and Predict Flash Floods in the Mediterranean

Abstract:

One of the costliest natural hazards around the globe is flash floods, resulting from localized intense convective precipitation over short periods of time. Since intense convective rainfall (especially over the continents) is well correlated with lightning activity in these storms, a European Union FP6 FLASH project was realized from 2006 to 2010, focusing on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project, 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms, lightning data were used together with rainfall estimates in order to understand the storms’ development and electrification processes. In addition, these case studies were simulated using mesoscale meteorological models to better understand the local and synoptic conditions leading to such intense and damaging storms. As part of this project, tools for short-term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long-term forecasts (a few days) of the likelihood of intense convection, were developed and employed. The project also focused on educational outreach through a special Web site http://flashproject.org supplying real-time lightning observations, real-time experimental nowcasts, medium-range weather forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented, long-range regional lightning networks can supply valuable data, in real time, for warning the public, end-users and stakeholders of imminent intense rainfall and possible flash floods.

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The FLASH Project: using lightning data to better understand and predict flash floods

Abstract:

The FLASH project was implemented from 2006 to 2010 under the EU FP6 framework. The project focused on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms lightning data from the ZEUS network were used together with satellite derived rainfall estimates in order to understand the storm development and electrification. In addition, these case studies were simulated using mesoscale meteorological models to better understand the meteorological and synoptic conditions leading up to these intense storms. As part of this project tools for short term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long term forecasts (a few days) of the likelihood of intense convection were developed. The project also focused on educational outreach through our website http://flashproject.org supplying real time lightning observations, real time experimental nowcasts, forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented as the climate changes, long-range regional lightning networks can supply valuable data, in real time, for warning end-users and stakeholders of imminent intense rainfall and possible flash floods.