This study aims to characterise the rainfall exceptionality and the meteorological context of the 20 February 2010 flash-floods in Madeira (Portugal). Daily and hourly precipitation records from the available rain-gauge station networks are evaluated in order to reconstitute the temporal evolution of the rainstorm, as its geographic incidence, contributing to understand the flash-flood dynamics and the type and spatial distribution of the associated impacts. The exceptionality of the rainstorm is further confirmed by the return period associated with the daily precipitation registered at the two long-term record stations, with 146.9 mm observed in the city of Funchal and 333.8 mm on the mountain top, corresponding to an estimated return period of approximately 290 yr and 90 yr, respectively. Furthermore, the synoptic associated situation responsible for the flash-floods is analysed using different sources of information, e.g., weather charts, reanalysis data, Meteosat images and radiosounding data, with the focus on two main issues: (1) the dynamical conditions that promoted such anomalous humidity availability over the Madeira region on 20 February 2010 and (2) the uplift mechanism that induced deep convection activity.

The aim of this study is to carry out two objective classifications concerning the occurrence of episodes of heavy rainfall in Southern Portugal. The first one seeks to define the main spatial distribution patterns associated with abundant rainfall days in this region. Using a 15‐year (from October 1983 to April 1998) precipitation data base corresponding to 98 sites in Southern Portugal, a sample is established by extracting the precipitation days in which the threshold of 40 mm/24 h was exceeded in three or more stations, yielding a total of 199 days. It is found that the Algarve region is the one where episodes of heavy rainfall are most frequent and which exhibits the strongest torrential character. The highest frequency of days with heavy rain occurs in the fall and in the early part of the winter. Through the combined use of principal component analysis (PCA) and k‐means clustering, four different rainfall patterns are identified, and each one exhibits specific characteristics.The second classification is obtained using the same computational method (PCA coupled with k‐means) and seeks to define the fundamental large‐scale atmospheric circulation types associated with abundant rainfall in the region, based on sea level pressure (SLP) data. The data was collected from the NCEP/NCAR Reanalysis dataset, taking SLP as the most discriminating variable. Five circulation types are thus obtained, indicating considerable diversity among the large‐scale atmospheric circulation conditions that are conducive to the occurrence of heavy rainstorms in Southern Portugal.The article concludes by discussing the main links between the two classification schemes, in order to ascertain the influence of the large‐scale atmospheric circulation upon the spatial distribution patterns of heavy precipitation episodes. Copyright © 2007 Royal Meteorological Society

Landslides occurred in the Lisbon area during the last 50 years were almost always induced by rainfall and have been used to establish rainfall thresholds for regional landslide activity. In 2006, three new rainfall-triggered landslide events occurred in the study area, namely on the 20 March, the 25–27 October, and the 28 November. Landslide events occurred in March and October 2006 include shallow translational slides and few debris flows, and the corresponding absolute antecedent rainfall was found to be above the threshold for durations ranging from 4 to 10 days. These events also fit the combined threshold of daily precipitation and 5 days calibrated antecedent rainfall values. Likewise the landslide event that took place in late November 2006 includes some slope movements with deeper slip surfaces, when compared with landslides dating from March and October. Moreover, the corresponding absolute antecedent rainfall was also found to be above the 40-day period rainfall threshold. Here we characterize in detail the short and long-term atmospheric circulation conditions that were responsible for the intense rainfall episodes that have triggered the corresponding landslide events. It is shown that the three rainfall episodes correspond to considerably different synoptic atmospheric patterns, with the March episode being associated to an intense cut-off low system while the October and November episodes appear to be related to more typical Atlantic low pressure systems (and associated fronts) travelling eastwards. Finally, we analyse the role played by the North Atlantic Oscillation (NAO) during those months marked by landslide activity. It is shown that the NAO index was consistently negative (usually associated with above average precipitation) for the months prior to the landslide events, i.e. between October 2005 and March 2006, and again between August and October 2006.