| ABSTRACT | The study of last few decades climate variability is of special relevance, not only to match recent precipitation and temperature anomalies with climate patterns anomalies, but also to find possible attribution of those changes according to the synoptic patterns changes suggested by Earth System Models. So that, the main objective of our study is to compare and contextualise recent climatic variability (1981-2017) in Western Mediterranean region, with that took place in a previous long reference period (1871-198). The NOAA twentieth Century Reanalysis Project v2(1871-2017) and NCEP-NCAR reanalyses (1948-2017) have been considered for this goal. In order to characterize climatic variability in the region, daily meteorological patterns of sea level pressure and geopotential height at 700 hPa has been classified for the 1948-2009 period using an Objective Classification Procedure based on a Self Organising Map(SOM) in a 4-D neural network. SOM has been used as the principal technique to reduce the climate variability complexity, thus this methodology allows getting a compromise between keeping low frequency patterns while reducing the degrees of freedom of the system. This process has been carried out each month separately, so as to obtain the inter-annual evolution of each synoptic pattern. As a result of the classification process, 33 weather types has been obtained, which in turn, can be grouped into anticyclonic, cyclogenic, westerly, easterly and blocking patterns. The frequency and temporal evolution of those patterns has been evaluated along the 1871-2017 period. The results obtained revealed that some weather patterns anomalies during the 1981-2017 period have no comparison in terms of duration and/or intensity in the preceding 1871-1980 records. Concretely it is observed an increase in almost all Anticyclonic related patterns during winter(NDGF) and late spring(MJ) and a diminution in the number of cyclonic types during winter and spring(AMJ), especially those related to Atlantic Cyclogenesis. Also strong decadal variability is well identified in the Mediterranean Cyclogesis types and cold advection types from Northern and Eastern Europe. |