Monthly precipitation trends on the Mediterranean fringe of the Iberian Peninsula during the second-half of the twentieth century (1951-2000)

We analysed monthly precipitation trends on the eastern Mediterranean fringe of the Iberian Peninsula (IP) by means of a new monthly precipitation database [Monthly Precipitation Dataset, Mediterranean Spain (MOPREDA(MES))]. This database was created following an exhaustive quality control of the archives from the Meteorological Agency of Spain (Instituto Nacional de Meteorologia, INM), and comprises 1113 complete and homogeneous monthly precipitation series (1951-2000), covering 180000 km(2) (one-third of IP area). The new data set currently offers the highest spatial density of stations on the IP and around the Mediterranean Sea (1 station/150-200 km(2)), and includes available information at 1500 m asl. The analyses of monthly precipitation trends indicate high spatial and temporal variability. No global trend in the Study area was found. except for March, when significant negative trends affect the whole study area. Trends for winter months (December-January-February) are dominated by an East-West gradient with a latitudinal temporal shift. Positive trends are mainly located in coastland areas and negatives ones predominate inland. April shows a North-positive South-negative gradient, and the reverse is true for June and September. Negative trends are dominant in October over most of the study area, except for the Pyrenees area. July and August show the most complex spatial distribution pattern, with well-delimited areas of positive trends to the south and northwest. We generally detected no significant trends in May and November. In order to analyse the nature of rainfall variability in the study area, we also studied the synchronous influence of different low-variability modes [the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO)]. On the Mediterranean fringe of the IP precipitation is mainly related to negative phases of the three low-frequency variability patterns analysed, and the MO and the WeMO emerge as predominant teleconnection patterns. These results suggest that monthly variations in rainfall may result from the simultaneous effects of different atmospheric modes of low variability, especially those linked to the Mediterranean region. Studies making use of high-density precipitation databases, as is the case in this paper, are useful for a better understanding of precipitation behaviour in a complex area like the Mediterranean fringe of the IP. The results also provide valuable information for downscaling and hydrological management. Copyright (C) 2008 Royal Meteorological Society