Links between circulation and changes in the characteristics of Iberian rainfall

Abstract

Investigation of the links between atmospheric circulation patterns and rainfall is important for the understanding of climatic variability and for the development of empirical circulation-based downscaling methods. Here, spatial and temporal variations in circulation-rainfall relationships over the Iberian Peninsula during the period 1958-97 are explored using an automated circulation classification scheme and daily rainfall totals for 18 stations. Links between the circulation classification scheme and the North Atlantic oscillation (NAO) are also considered, as are the direct links between rainfall and the NAO. Trends in rainfall and circulation-type frequency are explored. A general tendency towards decreasing mean seasonal rainfall over the peninsula, with the exception of the southeastern Mediterranean coast, hides larger changes in wet day amount and rainfall probability. There is a tendency towards more, less-intensive rain days across much of Iberia, with a tendency towards more, more-intensive rain days along the southeastern Mediterranean coast, both of which are reflected in changes in rainfall amount quantiles. A preliminary analysis indicates that these changes may have occurred systematically across all circulation types. Comparison of the trends in rainfall and in circulationtype frequency suggests possible links. These links are supported by linear regression analyses using circulation-type frequencies as predictor variables and rainfall totals for winter months as the predictands. The selected predictor variables reflect the main circulation features influencing winter rainfall across the peninsula, i.e. the strong influence of Atlantic westerly and southwesterly airmasses over much of the peninsula, of northerly and northwesterly surface flow over northern/northwestern Spain and northern Portugal and the stronger effect of Mediterranean rather than Atlantic influences in southeastern Spain. The observed rainfall changes cannot, however, be explained by changes in circulation alone.

Spatial and temporal variability of the daily rainfall regime in Catalonia (northeastern Spain), 1950–2000

“…Alpert et al (2002) use the rainfall intensity for different categories or classes in the Mediterranean area and find that, in Spain, the trends for the extreme classes (light and heavy rains) are positive, whereas the central classes (moderate rains) show significant decreases. The results of Goodess and Jones (2002) for the Iberian Peninsula show a tendency towards more, less-intensive rain across much of Iberia, with a tendency towards days of increasingly intensive rain along the southeastern Mediterranean coast. Brunetti et al (2000Brunetti et al ( , 2001 detected positive trends for rainfall intensity for several gauges in northeastern Italy.…”

The influence of atmospheric circulation at different spatial scales on winter drought variability through a semi‐arid climatic gradient in Northeast Spain

“…This has been applied in several regions such as the United Kingdom Wilby et al, 1995;Jones et al, 1993), USA (Wilby and Wigley, 1997), Scandinavia (Linderson, 2001) and Japan (Wilby et al, 1998). In the Iberian Peninsula, it has been widely used to classify weather types (Martín-Vide, 2002;Goodess and Palutikof, 1998;Goodess, 2000;Goodess and Jones, 2002;Trigo and DaCamara, 2000;Rasilla et al, 2002;Spellman, 2000a,b).…”

“…Nevertheless, the complex relief that characterises the Iberian Peninsula and the maritime influence can modulate these influences spatially. In the Mediterranean coastland, different authors have shown that flows from east, and cyclonic weather types have an important role in precipitation (Romero et al, 1999;Goodess and Jones, 2002). Moreover, the flows from east can be reactivated because of hot conditions in the sea-surface temperature, which is frequent in autumn and early winter (Martín-Vide and Llasat, 2000;Serra et al, 1996;Millán et al, 1995).…”

“…The negative trends of C, SW and W, which are prone to cause precipitation in the main part of the study area, and the positive trend of A and east directional weather types, which are negatively correlated with the winter-SPI values, could be the cause of the general negative trend of the winter-SPI values. In the whole of the Iberian Peninsula, Goodess and Jones (2002) indicated that the decrease in precipitation is mainly explained by the positive trend towards the occurrence of less-intensive rain days. They indicated that this could be associated with the decrease in the influence of the Atlantic westerly and southwesterly air-masses.…”

“…Other papers have analysed the influence of weather types on precipitation (Trigo and DaCamara, 2000;Goodess and Palutikof, 1998;Martín-Vide, 2002;Goodess and Jones, 2002;Corte-Real et al, 1998;Esteban et al, 2005). Nevertheless, at present there is no joint analysis of the relationship between the general atmospheric circulation modes in the North Atlantic region, the weathertype frequencies and the intensity and spatial differences of droughts, nor have detailed spatial scales been considered by means of a high density of weather stations, a method that would make it possible to accurately determine spatial and temporal patterns in a region of strong precipitation variability.…”