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Southern Africa has been strongly affected by ongoing climate change in recent decades. Rainfall variability is modulated by regional patterns of moisture advection and convergence in the lower troposphere. Using reanalysis, ground and satellite‐based rainfall products and observations from 10 weather stations, we perform a synoptic and climatological analysis focussing on atmospheric circulation, moisture transport and their relationship with rainfall anomalies over the Angolan and Namibian Plateau region. Results clearly show that a stronger (weaker) Zambezi low level jet (LLJ) magnitudes are associated with above (below) normal rainfalls over the main Angolan and Namibian plateaus. With lower confidence, a stronger Limpopo LLJ may also lead to enhanced rainfall over Namibia and southeast Angola. The Zambezi LLJ moisture fluxes are moderately controlled by Mozambique Chanel Trough and Angola Low intensities, while the Limpopo LLJ intensities have very low influence from the Mozambique Chanel Trough and Angola Low, respectively. The Angola Low in its tropical phase is associated with deeper moisture convergence and stronger vertical velocities, leading to higher amounts of precipitable water within the air column, thus enhancing precipitation over the region. It is shown that the major moisture source of rainfall, which is advected to via the Zambezi LLJ, is the Indian Ocean. Meanwhile, the Atlantic Ocean plays a minor role. Given the current lack of observations and projected climate change, further research and investments are urgently needed in the region, for example, regarding the expansion of the surface data network. [ABSTRACT FROM AUTHOR]

The Iberian Peninsula (IP) is often affected by extreme precipitation and severe winds that are mostly associated with extratropical cyclones and their atmospheric fronts. ERA5 reanalysis data are used to revise and update two existing rankings of extreme precipitation and extreme potential wind‐loss days for the extended winter months on the IP. A ranking of concurrent precipitation and wind extreme events is produced by matching the two individual rankings for the IP and for specific IP subregions, including its main river basins. The intensity and the variability at the interannual and decadal scale are evaluated for precipitation, wind and concurrent precipitation and wind events. A systematic analysis of the underlying synoptic conditions is pursued for the top100 most extreme concurrent events including (a) cyclones' trajectories, (b) the presence of an Atmospheric River (AR), (c) recurrent patterns in the locations affected by precipitation and wind extremes and (d) possible long‐term trends. Results show that 85% of concurrent precipitation and wind extreme events are clearly associated with a cyclonic feature and most of these cyclones either cross the IP or pass to the northwest. Concurrent events are more likely occurring in the northwestern sectors of the IP on wintertime as in recent decades a downward trend for the events' frequency is observed in autumn. ARs are more likely associated with the strongest events occurring on the western sector of IP. Accordingly, the areas that mostly experience concurrent precipitation and wind extremes related to those systems are located in the northwestern sector of the peninsula. [ABSTRACT FROM AUTHOR]

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]

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]

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]

The relationship between circulation weather types (WTs) and the spatial variability of precipitation across the Iberian Peninsula were studied using a high density, quality controlled, homogenized monthly precipitation database with approximately 3000 stations and interpolated to a 10 km grid. The circulation WTs were computed using an objective version of the Lamb classification centered on the Iberian Peninsula. A total of 26 WTs were selected for the period 1948-2003. Daily WTs were grouped to obtain their monthly frequencies, and used as potential independent variables in a linear least-square non-negative regression model with a forward stepwise selection. Results show the impact of each WT on precipitation in the Iberian Peninsula with a spatial resolution which had never been achieved before and additionally were obtained on a monthly scale highlighting the large seasonal cycle observed in each class, and including significantly different patterns in winter and summer. Nevertheless, results confirm that most of the precipitation in the Iberian Peninsula is produced by just a few WTs, with W, SW and C being the most influential. The association between WTs and precipitation is more robust in winter months and for the western IP areas, while it is lower during summer months and for the eastern IP areas. Spatial analysis revealed that precipitation on the Mediterranean coastland is mostly related with easterly flows (NE, E, SE and their hybrid counterparts), while on the Cantabrian coastland. N and NW flows are the most influential WTs. In general, cyclone-related types are the least frequent ones and also the most efficient in generating precipitation; while anticyclone-related types have the highest frequencies, but also the lowest contribution to total monthly rainfall in the Iberian Peninsula. [ABSTRACT FROM AUTHOR]

ABSTRACT This study provides a thorough assessment of recent changes in near-surface air temperature in mainland Portugal at both the local and regional level, focusing on extreme events (maximum and minimum) at a seasonal scale. It examines trends in selected specific indices that are calculated from daily air temperature data from 23 measuring stations scattered across the territory, recorded between 1941 and 2006. The results show overall warming trends over mainland Portugal that are consistent with the dominant global warming and reflect an increase in both maximum and minimum air temperature. When we split the study period into two sub-periods, 1945-1975 and 1976-2006, the partial trend analysis reveals that the first sub-period is mostly characterized by cooling followed by an even stronger tendency towards warmer benchmarks in all the indices evaluated, in particular for the warm-related temperature extremes in spring and summer. The changes observed in seasonal patterns confirm the well-known asymmetries in the climate in mainland Portugal and suggest that they are likely to be aggravated. There are changes associated with extreme temperatures, in particular, the significant increase in the frequency and duration of heat waves, and the increase in the frequency of hot days and tropical nights, especially in spring and summer; moreover there is a significant decrease in the frequency of cold waves and frost days. Teleconnections associated with changing patterns of temperature are also investigated. The results show that, over mainland Portugal, cold-related air temperature extremes have been associated with the East Atlantic mode in autumn, whereas warm-related extremes have been associated with the Scandinavia teleconnection pattern in spring, summer and autumn. However, the most prominent Northern Hemisphere pattern, the North Atlantic Oscillation, exerts limited influence, which is felt mostly in winter and spring. [ABSTRACT FROM AUTHOR]