The state of climate in NW Iberia

Abstract

Since 1974, there has been a significant increasing trend in land and sea surface temperatures of 0.5 and 0.24°C decade–1, respectively, in the NW Iberian Peninsula. Over the same period, annual precipitation does not show any trend, although some tendencies have been detected at seasonal scales. A significant positive trend, on average of 2 cm decade–1, was also observed in sea level rise from 1943 onwards. Ekman transport perpendicular to the coast (upwelling index) showed a decrease from 1975 to 2008 at both annual and seasonal scales. In addition, the flow of the Miño River (the main river in the area) has also decreased at a mean rate of 18 m3 s–1 decade–1 since 1970. At a synoptic scale, winter cyclone frequency and winter and spring blocking activity have decreased since the 1950s, which may partially explain the winter precipitation decline and the winter and spring temperature increases. These changes in synoptic systems are also in agreement with reported trends in the dominant variability modes of atmospheric circulation affecting NW Iberia, particularly a pronounced positive trend in the North Atlantic Oscillation from the 1970s to the 1990s.