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

Regional differential behaviour of maximum temperatures in the Iberian Peninsula regarding the Summer NAO in the second half of the twentieth century

V. Favà, J.J. Curto, M.C. Llasat

Abstract

The relationship between atmospheric circulation in northern Europe in summer and the maximum temperatures (Tx) of the Iberian Peninsula (IP) have received little attention. In this article we explore which synoptic structures related to high absolute values of SNAO (Summer North Atlantic Oscillation) are linked to significant anomalies in the maximum temperatures of the IP on a regional scale. Furthermore, we examine how the frequency of these structures has contributed to the differential evolution of maximum temperature trends in the IP and modulated the relationship between the SNAO and the maximum temperatures of the IP in the second half of the twentieth century.

Four basic synoptic structures were identified and their time series were calculated. Thus, we can explain why significant positive correlations between the SNAO and the maximum temperatures for the north of the IP are found for the 1951–1967 period, while in the 1962–1978 period these correlations are negative and affect the eastern part of the IP.

We found that, for the 1951–1967 period, the negative SNAO contributed to a lowering of the maximum temperatures in the NW and north IP and to a strengthening of the north-south IP maximum temperature gradient. During the 1970s and the start of the 1980s, owing to the much higher values of SNAO, the more negative anomalies in the coldest days shifted towards the east of the IP.

Keywords

• Summer NAO;
• Maximum temperatures;
• Regional trends;
• Temperature gradient;
• Pressure gradient;
• Iberian Peninsula

You can download here: http://www.sciencedirect.com/science/article/pii/S0169809516302319

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

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 i 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).

Descarregar-lo: http://www.springerlink.com/content/f2626224w2117244/fulltext.pdf

Assessing trends in insured losses from floods in Spain 1971–2008

Abstract.

Economic impacts from floods have been increasing over recent decades, a fact often attributed to a changing climate. On the other hand, there is now a significant body of scientific scholarship all pointing towards increasing concentrations and values of assets as the principle cause of the increasing cost of natural disasters. This holds true for a variety of perils and across different jurisdictions. With this in mind, this paper examines the time history of insured losses from floods in Spain between 1971 and 2008. It assesses whether any discernible residual signal remains after adjusting the data for the increase in the number and value of insured assets over this period of time. Data on insured losses from floods were sourced from Consorcio de Compensación de Seguros (CCS). Although a public institution, CCS compensates