Iberia winter rainfall trends based upon changes in teleconnection and circulation patterns

Winter rainfall on the Iberian Peninsula presents a significant decrease in its western and central areas throughout the second half of the 20th century, whereas over the eastern fringe it shows hardly any variation. This spatial distribution of precipitation trends are related to teleconnection indices trends and changes in the frequency of surface circulation patterns over Western Europe. We determined these circulation patterns by carrying out a daily objective synoptic classification by means of a principal components analysis (PCA) using sea-level pressure (SLP) data. In order to better understand Iberian winter precipitation trends, circulation patterns are associated with those teleconnection patterns that have an important influence on Iberian rainfall: Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and Western Mediterranean Oscillation (WeMO). The circulation pattern showing the biggest increases involves high pressure over Central Europe. This pattern is showing a positive AO and NAO phase, and simultaneously, a negative WeMO phase.