Monthly modes of variation of precipitation over the Iberian peninsula

An attempt is made to find the main monthly modes of variation of precipita tion over the Iberian Peninsula. The modes of variation of precipitation we re derived from principal component analysis. The dataset used consists of records of monthly precipitation from 40 meteorological stations over 74 yr (1919-92.). The stations are spatially representative of most of the Iberi an Peninsula. To take into account the seasonality of precipitation over th e Iberian Peninsula, one analysis was performed separately for each calenda r month. The modes of variation resulting from the different analyses were compared and clustered in groups according to their loading patterns. Seven main patterns were found to be of importance during various months of the year. These seven patterns explained more than 75% of the variance of the p recipitation held from December to April. However, less than 20% of the tot al variance is explained for July and August. It is concluded that, dependi ng on the month or season of interest, different modes of variation should be considered in order to achieve a better description of the monthly preci pitation field.