Circulation weather types and cloud‐to‐ground flash density over the Iberian Peninsula

Journal of Hydrometeorology

Herrera

et al. 2006

192

183

March monthly accumulated precipitation in the central and western regions of the Iberian Peninsula presents a clear continuous decline of 50% during the 1960-97 period. A finer analysis using daily data reveals that this trend is exactly confined to the month of March. However, this is merely the most visible aspect of a larger phenomenon over the North Atlantic/European sector. The European precipitation trends in March for the period 1960-2000 show a clear distribution of increasing precipitation in the northern regions (the British Isles and parts of Scandinavia) together with decreasing trends throughout the western Mediterranean Basin.Relevant circulation changes over the North Atlantic and European sectors explain these precipitation trends. First, a regional Eulerian approach by means of a weather-type (WT) classification shows that the major rainfall contributors in March display significantly decreasing frequencies for the Iberian Peninsula, in contrast to the corresponding "wet" weather types for the U.K./Ireland sector, which display increasing frequencies. Within a larger context, a Lagrangian approach, based on the analysis of storm tracks over Europe and the North Atlantic region, reveals dramatic changes in the location of cyclones in the last four decades that coincide with the corresponding precipitation trends in Europe. The North Atlantic Oscillation is suggested to be the most important large-scale factor controlling both the circulation changes and the precipitation trends over the Euro-Atlantic area in March. Finally, the potential impact of reduced precipitation for rivers and water resources in the Iberian Peninsula is considered.

Section: Discussionmentioning

confidence: 99%

Section: B the Circulation Weather-type Approachmentioning

confidence: 99%

Understanding Precipitation Changes in Iberia in Early Spring: Weather Typing and Storm-Tracking Approaches

Paredes

Journal of Hydrometeorology

Herrera

et al. 2006

192

183

“…The anticyclonic (A) type is the most frequent circulation pattern throughout the year, except for the summer months of July and August, which are also highly influenced by the northeast (NE), north (N) and east (E) circulation types. The predominance of the A type is associated with the migration of the Azores anticyclone toward the Iberian Peninsula (Tomás et al, 2004). During summer, Portugal is usually under the influence of the Azores anticyclone and while a frequent shallow thermal depression can develop over the central Iberian Peninsula, the A class appears as one of the most frequent CWT affecting Portugal also during summer months .…”

Section: Cwt Characterizationmentioning

confidence: 99%

The influence of circulation weather patterns at different spatial scales on drought variability in the Iberian Peninsula

Russo

Gouveia

et al. 2015

Front. Environ. Sci.

Europe has suffered several extreme weather events which were responsible for considerable ecological and economic losses in the last few decades. In Southern Europe, droughts are one of the most frequent extreme weather events, causing severe damages and various fatalities. The main goal of this study is to determine the role of Circulation Weather Types (CWT) on spatial and temporal variability of droughts by means of the multi-scalar Standardized Precipitation Evapotranspiration Index (SPEI). This study aims also to identify the main CWTs associated with winter and summer droughts over different regions of Iberian Peninsula. During the period between 1950 and 2012, the most frequent CWTs were found to be the Anticyclonic (A), Cyclonic (C), North (N) and Northeast (NE) types. The trend analysis for winter season shows a clear increase of frequency CWTs associated to dry events (A, East and Southeast) and a decrease of frequency of C and northern types while in summer a clear decrease of NE is observed. The spatial patterns of correlation between SPEI and CWT show large patterns of negative correlations with winter frequencies of A and eastern weather types, while the reverse occurs with C and western types. This feature is highlighted on a regional approach. The NE type presents negative correlations in Central, Northwestern and Southwestern regions during winter and positive correlations in Eastern region during summer. In opposition, the West type presents positive correlations in all regions (except Eastern region) during winter and does not present significant correlations during summer. In general, the predominant CWT associated to winter or summer drought conditions differs greatly between regions. The winter droughts are associated mainly with high frequency of E types and low frequency of W types for all areas, while the summer drought in eastern sectors are linked with low frequency of C type, as well as the western regions are related with the N type.

“…This classification is based on the corresponding objective classification defined for the British Isles (Jenkinson and Collison, 1977;Jones et al, 1993) and has been broadly used for studying climate variability in the Iberian region such as trends of precipitation (Spellman, 2000;Goodess and Jones, 2002;Paredes et al, 2006), extreme events assessment such as droughts (Garcia-Herrera et al, 2007), wet winters (Vicente- or even relationship with snow depth (López-Moreno and Vicente- Serrano, 2007) and modes of low frequency variability (Ramos et al, 2010). Furthermore, this methodology has also been used for the construction of climate change scenarios (Goodess and Palutikof, 1998;Miranda et al, 2002) and even linking storm lightning activity to atmospheric circulation (Tomás et al, 2004;Ramos et al, 2011).…”

Section: Circulation Data and Weather Type Classificationmentioning

confidence: 99%

Modelling monthly precipitation with circulation weather types for a dense network of stations over Iberia

Cortesi

Hydrol. Earth Syst. Sci.

González‐Hidalgo

et al. 2013

Abstract. Precipitation over the Iberian Peninsula (IP) is highly variable and shows large spatial contrasts between wet mountainous regions to the north, and dry regions in the inland plains and southern areas. In this work, we modelled the relationship between atmospheric circulation weather types (WTs) and monthly precipitation for the wet half of the year (October to May) using a 10 km grid derived from a highdensity dataset for the IP (3030 precipitation series, overall mean density one station each 200 km 2 ). We detected two spatial gradients in the relationship between WTs and precipitation. The percentage of monthly precipitation explained by WTs varies from northwest (higher variance explained) to southeast (lower variance explained). Additionally, in the IP the number of WTs that contribute significantly to monthly precipitation increase systematically from east to west. Generally speaking, the model performance is better to the west than to the east where the WTs approach produce the less accurate results. We applied the WTs modelling approach to reconstruct the long-term precipitation time series for three major stations of Iberia (Lisbon, Madrid, Valencia).