Publication: Understanding precipitation changes in Iberia in early spring: Weather typing and storm-tracking approaches
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American Meteorological Society
March monthly accumulated precipitation in the central and western regions of the Iberian Peninsula presents a clear continuous decline of 50% during the 1960-97 period. A finer analysis using daily data reveals that this trend is exactly confined to the month of March. However, this is merely the most visible aspect of a larger phenomenon over the North Atlantic/European sector. The European precipitation trends in March for the period 1960-2000 show a clear distribution of increasing precipitation in the northern regions (the British Isles and parts of Scandinavia) together with decreasing trends throughout the western Mediterranean Basin. Relevant circulation changes over the North Atlantic and European sectors explain these precipitation trends. First, a regional Eulerian approach by means of a weather-type (WT) classification shows that the major rainfall contributors in March display significantly decreasing frequencies for the Iberian Peninsula, in contrast to the corresponding "wet" weather types for the U.K./Ireland sector, which display increasing frequencies. Within a larger context, a Lagrangian approach, based oil the analysis of storm tracks over Europe and the North Atlantic region, reveals dramatic changes in the location of cyclones in the last four decades that coincide with the corresponding precipitation trends in Europe. The North Atlantic Oscillation is suggested to be the most important large-scale factor controlling both the circulation changes and the precipitation trends over the Euro-Atlantic area in March. Finally, the potential impact of reduced precipitation for rivers and water resources in the Iberian Peninsula is considered.
© 2006 American Meteorological Society. The authors thank the ECMWF for providing their reanalysis data. We also thank the Instituto Nacional de Meteorología (INM) for providing the precipitation data for the Spanish stations. We thank the European Climate Assessment (ECA) project (supported by the Network of European Meteorological Services EUMETNET). This work was supported by the Portuguese Science Foundation (FCT) through project VAST (Variability of Atlantic Storms and Their impact on land climate) Contract POCTI/ CTA/46573/2002, cofinanced by the European Union under program FEDER. The Universidad Autónoma de Madrid (UAM) also supported this work. Thanks to Julio Díaz for his help. Finally, the suggestions of two anonymous reviewers helped to improve the original manuscript.
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