The Iberian Peninsula precipitation and river flow regimes are characterized by large values of inter‐annual variability, with large disparities between wet and dry years, especially in southern Iberia. This situation is a major problem for water resources management in general, and for the production of hydroelectricity in particular. Hydroelectric production represents, in an average year of precipitation, 20% of the total Spanish electricity production (and 35% for Portuguese production). Its absolute value, however, can vary by a factor of three between wet and dry years. We have assessed the impact of the North Atlantic oscillation (NAO) on winter precipitation and river flow regimes for the three main international Iberian river basins, namely the Douro (north), the Tejo (centre) and the Guadiana (south). Results show that the large inter‐annual variability in the flows of these three rivers is largely modulated by the NAO phenomenon. Throughout most of the 20th century, the January‐to‐March river flow is better correlated with the December to February (DJF) NAO index than is the simultaneous (DJF) river flow. Correlation values for the period 1973–98 are highly significant (−0.76 for Douro, −0.77 for Tejo and −0.79 for Guadiana), being consistently of higher magnitude than those obtained over previous decades. This impact of the NAO on winter river flow was quantified in terms of total Spanish potential hydroelectricity production. The important control exerted by the NAO and the recent positive trend in the NAO index contribute to a significant decrease in the available flow. This reduction represents an important hazard for the two Iberian economies because of its negative impact on water‐dependent resources, such as intensive agriculture and hydroelectric power production. Copyright © 2004 Royal Meteorological Society

The association among ENSO, the Northern Hemisphere sea level pressure (SLP), and temperatures in Europe has been analyzed during the period 1873–1995. In the first part, the SST of the Niño-3 region has been used to select extreme cold and warm ENSO events and periods that can be regarded as normal. The study was carried out for winter with the constraints that the ENSO events were well developed during the winter of study, and that they are extreme events. Composites of winter SLP and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other. In the North Atlantic area, no statistically significant SLP anomaly patterns were found associated with warm events, while during cold events a statistically significant anomaly pattern resembling the positive phase of the North Atlantic oscillation (NAO) was found. The temperature analysis shows statistically significant negative anomalies during cold events over the Iberian Peninsula and p... Abstract The association among ENSO, the Northern Hemisphere sea level pressure (SLP), and temperatures in Europe has been analyzed during the period 1873–1995. In the first part, the SST of the Niño-3 region has been used to select extreme cold and warm ENSO events and periods that can be regarded as normal. The study was carried out for winter with the constraints that the ENSO events were well developed during the winter of study, and that they are extreme events. Composites of winter SLP and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other. In the North Atlantic area, no statistically significant SLP anomaly patterns were found associated with warm events, while during cold events a statistically significant anomaly pattern resembling the positive phase of the North Atlantic oscillation (NAO) was found. The temperature analysis shows statistically significant negative anomalies during cold events over the Iberian Peninsula and p...

This paper is part of a research programme devoted to the analysis of historical climate in Spain. A reconstruction of rainfall characteristics in Southern Spain from 1500 to the present is described. Weather information was taken from original documentary sources in the region. A numerical index was established to characterize the rainfall and its evolution. Results were calibrated with modern precipitation data and with the results of other studies of historical climate. The main objective is to obtain a long precipitation record. A preliminary analysis of the obtained series shows a fluctuating behavior with alternating dry and wet periods. The wettest periods occurred at the end of 16th century, the beginning of 17th century, and at the end of 19th century. The driest periods in the pre‐instrumental era occurred during the first half of the 16th century, and around 1750. A general decreasing trend in precipitation can be observed from 1960 onwards. Copyright © 1999 Royal Meteorological Society