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Atmospheric fronts are fundamental features of the weather variability in the mid‐latitudes and are frequently associated with high‐impact weather events such as hail, wind gusts or precipitation. A method to link precipitation with synoptic‐scale fronts on sub‐daily timescales is developed based on ERA‐Interim data (1979–2016). A case study, a climatology and a trend analysis are presented and discussed. Spatially, an optimal attribution radius is identified based on a random sampling technique. The method is demonstrated using a past weather event that occurred over western Europe. Annual and seasonal cycles are presented and confirm, in agreement with previous studies, that frontal precipitation accounts for a large fraction of all precipitation (up to 80%) in the mid‐latitudes, especially during autumn and winter. Finally, a negative trend in frontal precipitation is identified, mostly affecting the Gulf Stream region. Cold fronts drive most of the observed trends in this region and the trend pattern suggests a polewards displacement of the zone of enhanced precipitation. A method is presented to relate, in time and space, precipitation to mid‐latitudes synoptic‐scale fronts using 6‐hourly ERA‐Interim data, distinguishing warm and cold fronts (a). The method is validated using a case study occurred over the North Atlantic and European sector (b). Annual and seasonal climatological means for precipitation assigned to fronts are analysed (c). A trend analysis for the period 1979–2016 suggests a statistically significant decrease of precipitation south of the Gulf Stream SST zone, mostly driven by cold fronts. [ABSTRACT FROM AUTHOR]

Extreme winter precipitation across the western Iberian Peninsula is frequently connected to atmospheric rivers, which are bands of intense water vapour transport (integrated vapour transport, IVT). Recent research over Western Europe has shown that by using the IVT forecasts in the form of the extreme forecast index (EFI), a tool that identifies anomalous conditions, it is possible to provide earlier awareness of extreme precipitation events than by using the precipitation EFI directly. The aim of the present paper is to assess these findings further by identifying the regions of Iberia where such IVT forecasts are skilful and for what lead times. Employing the EFI on the European Centre for Medium‐Range Weather Forecasts (ECMWF) Integrated Forecasting System ensemble for winters 2015/2016 and 2016/2017 and using high‐density daily surface precipitation observations, the IVT EFI is shown to have slightly more skill (than the precipitation EFI) in discriminating extreme precipitation anomalies across the western Iberian Peninsula (Portugal and northwestern Spain) from forecast day 11 onwards. The reasoning is that the higher IVT predictability means that the IVT EFI is more able to detect the approximate location of extreme events at earlier lead times than the precipitation EFI. In contrast, for shorter forecast lead times, the precipitation EFI is more skilful. Also, when considering the entire Iberian Peninsula, the precipitation EFI is more skilful and more appropriate to monitor for potential extremes even at longer lead times. The extreme forecast index (EFI) applied to water vapour transport has the ability to provide earlier awareness of extreme precipitation in western Iberia. This synoptic‐scale structure seen here on forecast day 1 on February 12, 2016, is typical during many extreme precipitation events in western Iberia. The synoptic‐scale characteristics of the water vapour transport EFI enable it to capture the approximate location of extremes earlier (from forecast day 11) compared with using the precipitation EFI. [ABSTRACT FROM AUTHOR]

The Atmospheric River Tracking Method Intercomparison Project (ARTMIP) is an international collaborative effort to understand and quantify the uncertainties in atmospheric river (AR) science based on detection algorithm alone. Currently, there are many AR identification and tracking algorithms in the literature with a wide range of techniques and conclusions. ARTMIP strives to provide the community with information on different methodologies and provide guidance on the most appropriate algorithm for a given science question or region of interest. All ARTMIP participants will implement their detection algorithms on a specified common dataset for a defined period of time. The project is divided into two phases: Tier 1 will utilize the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis from January 1980 to June 2017 and will be used as a baseline for all subsequent comparisons. Participation in Tier 1 is required. Tier 2 will be optional and include sensitivity studies designed around specific science questions, such as reanalysis uncertainty and climate change. High-resolution reanalysis and/or model output will be used wherever possible. Proposed metrics include AR frequency, duration, intensity, and precipitation attributable to ARs. Here, we present the ARTMIP experimental design, timeline, project requirements, and a brief description of the variety of methodologies in the current literature. We also present results from our 1-month "proof-of-concept" trial run designed to illustrate the utility and feasibility of the ARTMIP project. [ABSTRACT FROM AUTHOR]

The Danube River Basin is the second longest catchment basin in Europe and exhibits intense climatological diversity. In recent decades, the frequency and intensity of daily precipitation extremes have suffered from an increment in many parts of the world, including Central and Eastern Europe. Wet spells are defined by the number of consecutive rainy days with different thresholds. The identification of wet spells and their trends in the rainfall time is very important for many sectors, such as agriculture, ecology, hydrology and water resources. Wet spells can lead to extreme events and cause floods and other disasters. In this study, we will attempt to characterise global precipitation in the context of wet spells and associated precipitation depth of wet spells in the Danube River Basin area using daily precipitation data, as well as analysing different approaches to identifying wet spells. The ten most intense wet spells were detected, and the most intense, which occurred on 23 September 1996, was studied in depth in terms of precipitation and associated anomalies, the synoptic situation and the anomalous transport of moisture using a Lagrangian approach. The existence of a marked west-east dipole in the field of sea level pressure between the Atlantic Ocean and the eastern Mediterranean leads to the anomalous moisture transport from the Northern Atlantic Ocean to the Mediterranean Sea, where a higher available amount of moisture existed, and subsequently penetrated within the low positioned over the Danube River Basin. In addition, an Atmospheric River was also responsible for the wet conditions in the Danube River Basin. The combination of all these factors was responsible for the extreme precipitation linked with the wet spell. [ABSTRACT FROM AUTHOR]

ABSTRACT An objective method for ranking extreme precipitation episodes in different time scales over the Iberian Peninsula (IP) is presented. It relies on the extensive use of the high-resolution (0.2°) gridded daily precipitation database available for the IP, spanning from 1950 to 2008. The sum of the normalized anomalies is computed over different time scales (2-10 days) to allow ranking the different anomalous precipitation multi-day periods. The magnitude of a precipitation episode is given taking into account the area (in percentage) that has precipitation anomalies above two standard deviations (std) and the mean values of these anomalies over this area. With these criteria, we are able to evaluate the spatial extent of the precipitation episodes as well as their spatially integrated intensity. Different precipitation rankings are built for the entire IP, for Portugal and independently for six of the major river basins in the IP. The different rankings correctly detect and categorize the most extreme precipitation episodes which occurred on the various domains. For each domain, in general, results show that few events dominate the top ten of a particular ranking; specific extreme events at shorter time scales (e.g. 2-3 days) may be absent from the top rankings at longer time scales (e.g. 10 days). When comparing the different domains, the top ten events are generally different from each other, thus highlighting the spatial variability of extreme precipitation in the IP. Moreover the methodology used to build the rankings imply that some events are considered extreme due to particularly high precipitation totals, while other episodes are more dependent on extensive areas affected by less extreme precipitation values. The different rankings revealed to be an useful tool for future studies in identifying the meteorological impacts of extreme precipitation episodes at the regional scale covering relatively large areas. [ABSTRACT FROM AUTHOR]

In this work we performed an analysis on the impacts of blocking episodes on seasonal and annual European precipitation and the associated physical mechanisms. Distinct domains were considered in detail taking into account different blocking center positions spanning between the Atlantic and western Russia. Significant positive precipitation anomalies are found for southernmost areas while generalized negative anomalies (up to 75 % in some areas) occur in large areas of central and northern Europe. This dipole of anomalies is reversed when compared to that observed during episodes of strong zonal flow conditions. We illustrate that the location of the maximum precipitation anomalies follows quite well the longitudinal positioning of the blocking centers and discuss regional and seasonal differences in the precipitation responses. To better understand the precipitation anomalies, we explore the blocking influence on cyclonic activity. The results indicate a split of the storm-tracks north and south of blocking systems, leading to an almost complete reduction of cyclonic centers in northern and central Europe and increases in southern areas, where cyclone frequency doubles during blocking episodes. However, the underlying processes conductive to the precipitation anomalies are distinct between northern and southern European regions, with a significant role of atmospheric instability in southern Europe, and moisture availability as the major driver at higher latitudes. This distinctive underlying process is coherent with the characteristic patterns of latent heat release from the ocean associated with blocked and strong zonal flow patterns. We also analyzed changes in the full range of the precipitation distribution of several regional sectors during blocked and zonal days. Results show that precipitation reductions in the areas under direct blocking influence are driven by a substantial drop in the frequency of moderate rainfall classes. Contrarily, southwards of blocking systems, frequency increases in moderate to extreme rainfall classes largely determine the precipitation anomaly in the accumulated totals. In this context, we show the close relationship between the more intrinsic torrential nature of Mediterranean precipitation regimes and the role of blocking systems in increasing the probability of extreme events. [ABSTRACT FROM AUTHOR]

This work aims at characterizing the exceptional drought that affected Madeira Archipelago (Portugal) during the 2011–2012 hydrological year while including some major impacts but also the main atmospheric circulation mechanism behind the event. Precipitation records from six meteorological stations are used to assess the extreme drought episode by means of a decile classification. The assessment of the drought duration and severity is further corroborated by the Standardized Precipitation Index (SPI) computed for the 3, 6, 12 and 24 months’ time scales which confirmed that the 2012 drought event was one of the events with higher drought intensity at all scales, being classified as extreme at the 6-month time sale (SPI6 < −1.65) from December 2011 until May 2012 on the majority of the meteorological stations analysed. Long-term precipitation data available since 1865 for the station of Funchal confirm the exceptional dryness of this episode, particularly during the winter season (December to March) corresponding to the driest winter in 150 years. Vegetation activity is assessed through anomalies of NDVI (Normalized Difference Vegetation Index), confirming several large sectors of Madeira under vegetative stress. The southern sector of Madeira Island suffered up to seven months (out of nine) of extremely negative anomalies. From an operational point of view, obtained results reveal the ability of the developed methodology to monitor vegetation stress and droughts in Madeira. The extreme dryness of the Island favoured an unusually intense summer fire season of 2012 (between June and September) in Madeira being the year with highest number of fires in the last decade (with robust data). Furthermore, the main fire hotspots of the 2012 fire season are mostly coincident with the areas affected by drought. The large-scale atmospheric circulation responsible for the setting and intensification of the drought is evaluated using reanalysis data. An extensive high pressure anomaly (maximum above 12 hPa in December) persisted over the North Atlantic during the extended winter months (October to April), centred between the Azores Islands and the UK. This feature is in agreement with a positive NAO index (2.25 in December), a negative EA index (−1.76 in January and −1.73 in February) and compatible with enhanced north-easterly trade winds over the region. As a consequence of this uncharacteristic dynamics there was a deficit of moisture availability over the region as evaluated by the vertically integrated horizontal water vapour transport with a negative anomaly up to −120 kg m −1 s −1 . [ABSTRACT FROM AUTHOR]

This study deals with the question of how winegrowing in Spain may be altered by anthropogenic climate change. The present state and expected future development of three bioclimatic indices relevant for winegrowing were assessed by observation, and four regional climate models from the EU-ENSEMBLES project were investigated. When comparing the 2061-2090 scenario period to the 1961-1990 reference period, the models unanimously indicate a significant increase in the mean of the two considered thermal indices over the entire study region. However, for the index based on temperature and precipitation, the models are heavily biased when verified against observations and generally disagree on the size of the projected future change. For this index, unanimous model agreement was only found for northwestern Spain where all models indicated a significant decrease in the mean. From these results, regional climate change is expected to negatively affect the quality of wine in the growing regions of central and southern Spain, and the Ebro valley, whereas positive effects should be expected in the northwest. No significant changes in the risk of mildew infestation are to be expected except for the northwest, where this risk is projected to decrease. [ABSTRACT FROM AUTHOR]

An automated atmospheric rivers (ARs) detection algorithm is used for the North Atlantic Ocean basin that allows the identification and a comprehensive characterization of the major AR events that affected the Iberian Peninsula over the 1948-2012 period. The extreme precipitation days in the Iberian Peninsula and their association (or not) with the occurrence of ARs is analyzed in detail. The extreme precipitation days are ranked by their magnitude and are obtained after considering 1) the area affected and 2) the precipitation intensity. Different rankings are presented for the entire Iberian Peninsula, for Portugal, and for the six largest Iberian river basins (Minho, Duero, Tagus, Guadiana, Guadalquivir, and Ebro) covering the 1950-2008 period. Results show that the association between ARs and extreme precipitation days in the western domains (Portugal, Minho, Tagus, and Duero) is noteworthy, while for the eastern and southern basins (Ebro, Guadiana, and Guadalquivir) the impact of ARs is reduced. In addition, the contribution from ARs toward the extreme precipitation ranking list is not homogenous, playing an overwhelming role for the most extreme precipitation days but decreasing significantly with the less extreme precipitation days. Moreover, and given the narrow nature of the ARs, the location of the ARs over each subdomain is closely related to the occurrence (or not) of extreme precipitation days. [ABSTRACT FROM AUTHOR]

ABSTRACT Flood events is the natural hazard that originated more damages and fatalities in the Iberian Peninsula in the last decades. While most 20th century extreme precipitation and flood episodes in Iberia have been documented, the same does not hold for most events that took place during the 19th century. This article describes the unusually high precipitation and associated impacts recorded during the 1855/1856 hydrological year. We combine newspaper reports, early instrumental precipitation series and sea level pressure ( SLP) reconstructed gridded fields. The early instrumental precipitation time series includes 11 observatories that were not previously digitized and preceded the implementation of the official meteorological observation network in Spain. We show that high values of precipitation were mostly recorded during the months of September, October 1855 and January 1856, with most of the flooding and damages occurring in the last month. The use of daily circulation weather types and monthly differences of SLP are particularly useful to explain the heavy precipitation in October and January, which were clearly associated with unusual high frequencies of wet weather types. However, SLP patterns cannot explain the September records, which could be associated to upper cold air intrusions in the Iberian Peninsula. [ABSTRACT FROM AUTHOR]

Precipitation extremes in mainland Portugal (south-western Europe) using daily precipitation data recorded in the period 1941-2007 (67 years) at 57 meteorological stations scattered across the area are studied at an annual scale. Trends in selected precipitation annual indices that are calculated from these data are investigated, in particular trends in the intensity, frequency and duration of extreme precipitation events. Special attention is dedicated to local and regional variability. The spatial correlations between the annual trends in mean precipitation and in the extremes are analysed. Moreover, the relationships between the variability of the North Atlantic Oscillation (NAO) index and several indices related to the frequency and intensity of the precipitation at the 57 stations were also investigated. Results show that several stations have predominantly negative tendencies in the precipitation indices, although the majority of stations did not show statistically significant change over time in the 1941-2007 period. At the regional level, the decreasing trend in the simple daily precipitation intensity index is the only one statistically significant at the 5 % level and appears to be related to the predominance of the positive phase of the NAO. For the period 1976-2007, the proportion of the total precipitation attributed to heavy and very heavy precipitation events increased and, consequently, daily precipitation events show a tendency to become more intense. Moreover, correlation analysis show that the most extreme events could be changing at a faster absolute rate in relation to the mean than more moderate events. [ABSTRACT FROM AUTHOR]

A method for ranking daily precipitation events is presented based on the most comprehensive database of daily gridded precipitation dataset available for the Iberian Peninsula spanning from 1950 to 2008. The magnitude of an event is obtained after considering the area affected as well as its intensity in every grid point and taking into account the daily normalized departure from climatology. Different precipitation rankings are presented considering the entire Iberian Peninsula, Portugal and also the six largest river basins in the Iberian Peninsula. [ABSTRACT FROM AUTHOR]

An analysis of the frequency of cyclones and surface wind velocity for the Euro–Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October–March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January–March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50°N up to −3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern. [ABSTRACT FROM AUTHOR]

In recent years, the Arctic has become a subject of special interest due to the drastic effect of climate change over the region. Despite that there are several mechanisms that influence the Arctic region; some recent studies have suggested significant influences of moisture transport over the observed loss of sea ice. Moisture transport can affect the region in different ways: direct precipitation over the region, radiative effect from the cloud cover and through the release of latent heat. Atmospheric rivers (ARs) represent one of the main events involved in moisture transport from the tropics to the mid-latitudes and despite having been shown especially relevant on the northward advection, their effect over the Arctic has not been deeply investigated. The aim of this work was to establish the groundwork for future studies about the effect of ARs linked to moisture transport over the Arctic region. For this purpose, an automated algorithm was used to identify regions of maximum AR occurrence over the Arctic. This was done by analysing the number of AR detections every month over a band of 10° of latitude centred on 60° N. The Lagrangian model FLEXPART was used to find the areas where the ARs take their moisture to the Arctic. Using this model, the anomalous moisture contribution to these baroclinic structures was analysed taking into account only the dates of AR occurrence. From the results, it appears that the main moisture sources for AR events extend over the North Atlantic and North Pacific oceans; moreover, the local input of moisture over the region of maximum AR occurrence seems to be especially relevant. In general terms, moisture comes from major evaporative areas over the western part of the oceanic regions in the band between 30° and 40° N for most months in the year, showing a continental origin in the summer months. This behaviour agrees with the climatological moisture transport into the Arctic determined in previous studies. However, in special association with AR events, an intensification of local moisture uptake is observed over the area of maximum AR activity and nearby. The study of the origin of this moisture and associated anomalies for Arctic ARs is an important step in the analysis of the effect of these structures on the Arctic environment. [ABSTRACT FROM AUTHOR]

An assessment of daily accumulated precipitation during extreme precipitation events (EPEs) occurring over the period 2000–2008 in the Iberian Peninsula (IP) is presented. Different sources for precipitation data, namely ERA-Interim and ERA5 reanalysis by the European Centre for Medium-Range Weather Forecast (ECMWF) and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA), both in near-real-time and post-real-time releases, are compared with the best ground-based high-resolution (0.2° × 0.2°) gridded precipitation dataset available for the IP (IB02). In this study, accuracy metrics are analysed for different quartiles of daily precipitation amounts, and additional insights are provided for a subset of EPEs extracted from an objective ranking of extreme precipitation during the extended winter period (October to March) over the IP. Results show that both reanalysis and multi-satellite datasets overestimate (underestimate) daily precipitation sums for the least (most) extreme events over the IP. In addition, it is shown that the TRMM TMPA precipitation estimates from the near-real-time product may be considered for EPEs assessment over these latitudes. Finally, it is found that the new ERA5 reanalysis accounts for large improvements over ERA-Interim and it also outperforms the satellite-based datasets. [ABSTRACT FROM AUTHOR]

In the most recent decades, central Europe and the Danube River Basin area have been affected by an increase in the frequency and intensity of extreme daily rainfall, which has resulted in the more frequent occurrence of significant flood events. This study characterised the link between moisture from the Mediterranean Sea and extreme precipitation events, with varying lengths that were recorded over the Danube River basin between 1981 and 2015, and ranked the events with respect to the different time scales. The contribution of the Mediterranean Sea to the detected extreme precipitation events was then estimated using the Lagrangian FLEXPART dispersion model. Experiments were modelled in its forward mode, and particles leaving the Mediterranean Sea were tracked for a period of time determined with respect to the length of the extreme event. The top 100 extreme events in the ranking with durations of 1, 3, 5, 7, and 10 days were analysed, and it was revealed that most of these events occurred in the winter. For extreme precipitation, positive anomalies of moisture support from the Mediterranean were found to be in the order of 80% or more, but this support reached 100% in summer and spring. The results show that extreme precipitation events with longer durations are more influenced by the extreme Mediterranean anomalous moisture supply than those with shorter lengths. However, it is during shorter events when the Mediterranean Sea contributes higher amounts of moisture compared with its climatological mean values; for longer events, this contribution decreases progressively (but still doubles the climatological moisture contribution from the Mediterranean Sea). Finally, this analysis provides evidence that the optimum time period for accumulated moisture to be modelled by the Lagrangian model is that for which the extreme event is estimated. In future studies, this fine characterisation could assist in modelling moisture contributions from sources in relation to individual extreme events. [ABSTRACT FROM AUTHOR]

The European Macaronesia Archipelagos (Azores, Madeira and Canary Islands) are struck frequently by extreme precipitation events. Here we present a comprehensive assessment on the relationship between atmospheric rivers and extreme precipitation events in these three Atlantic Archipelagos. The relationship between the daily precipitation from the various weather stations located in the different Macaronesia islands and the occurrence of atmospheric rivers (obtained from four different reanalyses datasets) are analysed. It is shown that the atmospheric rivers' influence over extreme precipitation (above the 90th percentile) is higher in the Azores islands when compared to Madeira or Canary Islands. In Azores, for the most extreme precipitation days, the presence of atmospheric rivers is particularly significant (up to 50%), while for Madeira, the importance of the atmospheric rivers is reduced (between 30% and 40%). For the Canary Islands, the occurrence of atmospheric rivers on extreme precipitation is even lower. [ABSTRACT FROM AUTHOR]

Abstract: Changes in the climatology of precipitation and surface air temperature are being investigated worldwide, searching for changes in variability, the mean and extreme events (maximum and minimum). By exploring recent adjustments in the climate of mainland Portugal, particularly in the intensity, frequency and duration of extreme events, this study investigates trends in selected specific indices that are calculated from daily precipitation data from 57 and surface air temperature data from 23 measuring stations scattered across the territory. Special attention is paid to regional differences and variations in seasonality. The data cover the periods 1941–2007 for precipitation, and 1941–2006 for temperature. They are explored at the annual and seasonal scales and for different sub-periods. Results show that trends in annual precipitation indices are generally weak and, overall, not statistically significant at the 5% level. Nevertheless, a decreasing trend is revealed by regional indices of total wet-day precipitation and extreme precipitation (above the 99th percentile). Seasonal precipitation exhibits significant decreasing trends in spring precipitation, while extreme heavy precipitation events, in terms of both magnitude and frequency, have become more pronounced in autumn. Results for winter and summer suggest that the extremes have not suffered any significant aggravation. Trends for air temperature are statistically more significant and marked than for precipitation and indicate general warming across the territory. This warming trend is revealed very consistently by the time series of individual stations and regional mean temperature, and is also consistent with the findings reported in other studies for Portugal and at the European scale. [Copyright &y& Elsevier]

Variability and predictability of extreme weather events are research topics for which significant advances are strongly demanded by the scientific community. The socio-economic impacts of these events as fatalities, proprieties damages, rebuilding and reinsurance costs are becoming critical in the context of ongoing climate change. Within this framework, precipitation extremes associated with extra-tropical cyclones that affect the Iberian Peninsula are considered in this study. The aim of this research is to provide for an automated methodology to objectively assign precipitation and atmospheric fronts to the corresponding cyclones in order to study the characteristics of winter storms associated with extreme precipitation in the Iberian Peninsula.Firstly, a method to objectively assign the amount of precipitation to mid-latitude fronts at sub-daily basis is used (Hénin et al., 2018a). The method relies on the co-location of 6-hourly accumulated precipitation and fronts (both warm and cold fronts) inside a search box of predefined dimension. Results for the period 1979-2016 show that wintertime frontal precipitation accounts for up to 70% of total precipitation over the western European extremities. Secondly, an automated procedure is developed to objectively assign, at sub-daily basis, the fronts to the center of the parent cyclone. The approach is similar to the one used to relate precipitation and fronts: a search box is used to look for the cyclone center in the neighborhood of a frontal feature. A catalog of storms is obtained for the Northern Hemisphere from 1979 to date, based on mean sea level minima for cyclones' center's detection and on the nearest neighbor search for cyclones tracking (Trigo, 2006).Results show that the assignment of fronts to cyclones is not always straightforward and it strongly depends on the different mechanisms driving the overall weather pattern. For example, local pressure minima may form in the edge of a pre-existing cyclone making ambiguous to state which cyclone each front is attending. Therefore, a subset of extreme events in Iberia is analyzed taking into account three different situations: precipitation extremes, wind extremes and compound events due to extreme precipitation and wind. Different precipitation sources, including the new ERA5 reanalysis product by the European Centre for Medium-Range Weather Forecasts (ECMWF) currently available from 2000 to date, are considered, according to the assessment of satellite-based estimates and high-resolution precipitation datasets over Iberia presented in Hénin et al. (2018b). REFERENCESHénin, R.; Ramos, A.M.; Schemm, S.; Gouveia, C.M. Liberato, M.L.R. Assigning precipitation to mid-latitudes fronts on sub-daily scales in the North Atlantic and European sector: Climatology and trends. Int. J. Climatol. 2018a, 1-14. DOI: 10.1002/joc.5808.Hénin, R.; Liberato, M.L.R.; Ramos, A.M.; Gouveia, C.M. Assessing the Use of Satellite-Based Estimates and High-Resolution Precipitation Datasets for the Study of Extreme Precipitation Events over the Iberian Peninsula. Water. 2018b, 10(11), 1688. DOI: 10.3390/w10111688.Trigo, I. Climatology and interannual variability of storm-tracks in the Euro-Atlantic sector: a comparison between ERA-40 and NCEP/NCAR reanalyses. Climate Dynamics. 2006, 26: 127–143. DOI 10.1007/s00382-005-0065-9.ACKNOWLEDGMENTSThis work is supported by the Portuguese Science and Technology Foundation (Fundação para a Ciência e a Tecnologia – FCT), under the projects UID/GEO/50019/2013 – Instituto Dom Luiz and CMU/CS/0012/2017 – "eCSAAP - expert Crowdsourcing for Semantic Annotation of Atmospheric Phenomena". FCT is also providing for R. Hénin doctoral grant (PD/BD/114479/2016) and A.M. Ramos postdoctoral grant (FCT/DFRH/SFRH/BPD/84328/2012). [ABSTRACT FROM AUTHOR]

Wind extremes, heavy precipitation events and flooding occurring during extended winter over land in the mid latitudes are mostly associated with extratropical cyclones. It is well known that the Iberian Peninsula is prone to the occurrence of these compound events and associated hazards (Liberato et al., 2013; 2014). In this work a dataset of historical high-impact winter storms for the Iberian Peninsula is used to develop a systematic analysis and a catalogue of weather compound events. Additionally ERA5 reanalysis allow the assessment of the synoptic evolution, dynamical characteristics and the main impacts of the top-10 storms that provoked extreme impacts and considerable economical losses over Portugal.Liberato et al. 2013 Nat. Hazards Earth Syst. Sci., 13:2239-2251 doi: 10.5194/nhess-13-2239-2013Liberato 2014 Weather and Climate Extremes, 5-6: 16-28 doi: 10.1016/j.wace.2014.06.002AcknowledgmentsThis work is supported under projects UID/GEO/50019/2019 – Instituto Dom Luiz and WEx-Atlantic (PTDC/CTA-MET/29233/2017) by Fundação para a Ciência e a Tecnologia, Portugal (FCT) and Portugal Horizon 2020. FCT is also funding R. Hénin doctoral grant (PD/BD/114479/2016) and A.M. Ramos postdoctoral grant (FCT/DFRH/SFRH/BPD/84328/2012). [ABSTRACT FROM AUTHOR]

Summary The deadliest storm affecting Portugal since, at least, the early 19th century, took place on the 25 and 26 November 1967 causing more than 500 fatalities. This work aims to assess the most relevant aspects of this episode. This includes describing the associated meteorological conditions and key hydrological characterisation such as the level of exceptionality of the observed precipitation at different temporal scales, or the estimation of peak discharge values in 20 small river catchments affected. Additionally, from a human impact perspective we provide a full account of all the main socio-economic impacts, particularly the numbers and location of victims (dead, injured, homeless and evacuated). Based on the sub-daily time series of a representative station, and its Intensity–Duration–Frequency curves, we have found that the exceptionality of this rainfall event is particularly linked to rainfall intensities ranging in duration from 4 to 9 h compatible with return periods of 100-years or more. This range of time scale which are similar to the estimated concentration time values of the hydrographic basins affected by the flash flood event. From a meteorological perspective, this episode was characterised by strong convection at the regional scale, fuelled by high availability of moisture over the Lisbon region associated with a low pressure system centered near Lisbon that favoured the convective instability. Most victims were sleeping or were caught by surprise at home in the small river catchments around the main Lisbon metropolitan area. The majority of people who died or who were severely affected by the flood lived in degraded housing conditions often raised in a clandestine way, occupying flood plains near the stream beds. This level of destruction observed at the time is in stark contrast to what was observed in subsequent episodes of similar amplitude. In particular, since 1967 the Lisbon area, was struck by two comparable intense precipitation events in 1983 and 2008 but generating considerably fewer deaths and evacuated people. [ABSTRACT FROM AUTHOR]

The assessment of sources of moisture is key to the understanding of the hydrological cycle at different time scales, because it enables the establishment of source-sink relationships and the identification of the main moisture transport conveyors and associated processes, the result of which is precipitation. Gimeno et al. (2012) provided a comprehensive review of the state-of-the-art in the assessment of moisture source-sinks and how different approaches can contribute to improving our knowledge of this component of the Earth's Climate System. Since then, a variety of studies have focused on more specific aspects of the moisture budget and the source-sink distribution across the globe by integrating observations, satellite-derived products, physical tracers and numerical modelling. Here, we summarise the main advances in the field related to the impact of the moisture source-sink relationship on rainfall distribution, and add to the scientific debate on the question of the residence time of water vapour. We also revisit some of the recent advances in the role of the major mechanisms of moisture transport at a global scale, mainly Atmospheric Rivers and Low-Level Jet systems (Gimeno et al., 2016), in terms of their effects on precipitation extremes. Finally, we set out some of the main challenges for future research. [ABSTRACT FROM AUTHOR]