Seasonal precipitation variability in the east of the Iberian Peninsula is weakly linked to the North Atlantic Oscillation (NAO) during autumn and winter. For the purpose of improving the study of its performance, low-frequency variability patterns specific to the Mediterranean basin have been searched for. In this way, the Western Mediterranean Oscillation (WeMO) has been defined by means of the dipole composed, in its positive phase, by the anticyclone over the Azores and the depression over Liguria, and its index (WeMOi), as a result of the difference of the standardised values in surface atmospheric pressure in San Fernando (Spain) and Padua (Italy). This new index allows the detection of the variability relevant to the cyclogenesis next to the western Mediterranean basin, which determines in a predominant way the types of rainfall in the Gulf of Valencia. In this area, the WeMO is significantly better than the NAO to explain the monthly pluviometric anomalies during these seasons. Also, a daily resolution of the WeMOi can provide a useful tool to forecast torrential rainfall events in the north-western zones of the Mediterranean (eastern part of the Iberian Peninsula and the south of France), and such significantly daily rainfall frequencies for different thresholds.

Near-surface wind speed trends recorded at 67 land-based stations across Spain and Portugal for 1961-2011, also focusing on the 1979-2008 subperiod, were analyzed. Wind speed series were subjected to quality control, reconstruction, and homogenization using a novel procedure that incorporated the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5)-simulated series as reference. The resultant series show a slight downward trend for both 1961-2011 (20.016

ABSTRACT: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 Meteorología, INM), and comprises 1113 complete and homogeneous monthly precipitation series , covering 180 000 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.

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