Links between circulation types and precipitation over Spain

This paper illustrates the ability of a set of different atmospheric circulation classifications from the COST733 Action “Harmonisation and Applications of Weather Types Classifications for European Regions” to describe the variability of winter precipitation over different climatic regions of Spain for the period 1961-1990. A Principal Component Analysis was first applied to identify the three regions (Atlantic, Mediterranean and Northern) with similar precipitation climatology. Different metrics such as the explained variation (EV), Pseudo-F index (PF) and the standard deviation (STD) have been used to evaluate the discriminatory power of the circulation classifications. A ranking of circulation classifications has been established for each region and for each metric. In the Atlantic and Northern regions, classifications that show a better performance correspond to the same type of algorithms, i.e. derived types with non-hierarchical cluster analysis. Instead, in the Mediterranean region, classifications using pre-defined types based on thresholds perform better. The classifications with the worst performance in every region belong to the subjective type. An analysis of the impact of the number of CTs on the discrimination ability of the classifications has also been carried out. Depending on the metric used, a different sensitivity of the classifications to the number of CTs has been found. The EV index shows an improvement when the number of CTs increases. Instead, the PF and the STD metrics showed a negative impact with an increasing number of CTs.