Low-frequency variability of seasonal rainfall over the Iberian Peninsula and ENSO

This study is concerned with the influence of Fl Nino-Southern Oscillation (ENSO) on seasonal precipitation over the Iberian Peninsula (IP), and the s tability of this association over time. Principal Component Analysis (PCA) is applied to rainfall data in order to identify regions of coherent intera nnual variability. Two regions are identified in the IF, namely its south-e astern part, and the remaining region. Lag correlations have been applied t o rainfall and the Southern Oscillation Index (SOI), the latter leading the former. For the entire period, 1900-1996, ENSO appears to be related to ab ove-average autumn precipitation in both regions, and below-average spring rainfall over the south-eastern IF. For winter, the ENSO signal in the regi on is weak, and not statistically significant. Strongest correlations occur for leads of 3-6 months. However, when the ENSO-rainfall association is an alysed over a 20-year moving window from 1900 to 1996, it becomes clear tha t it has changed substantially over time. For the last decades of the perio d, ENSO has been associated with below-average spring and winter rainfall o ver the south-eastern IF, and above-average autumn rainfall in the Peninsul a as a whole. Over the south-eastern IF, the association for autumn has wea kened considerably recently. The strength of the ENSO-rainfall association appears to be related to the frequency and/or intensity of ENSO events duri ng the 1900-1996 period. Copyright (C) 1999 Royal Meteorological Society.