Abstract
Abstract. Surface climate in Europe is changing and patterns in trends have been found to vary at sub-seasonal scales. This study aims to contribute to a better understanding of these changes across space and time by analysing to what degree observed climatic trends can be attributed to changes in synoptic atmospheric circulation. The relative importance of synoptic circulation changes (i.e. trends in synoptic type frequencies) as opposed to trends in the hydrothermal properties of synoptic types (within-type trends) on precipitation and temperature trends in Europe is assessed on a monthly basis. The study is based on mapping spatial and temporal trend patterns and their variability at a relatively high resolution (0.5° × 0.5°; monthly) across Europe. Gridded precipitation and temperature data (1963–2001) originate from the Watch Forcing Data set and synoptic types are defined by the objective SynopVis Grosswetterlagen (SVG). During the study period, relatively high influence of synoptic circulation changes are found from January to March, contributing to wetting trends in northern Europe and drying in the south. Simultaneously, particularly dry synoptic types get warmer first in south-western Europe in November and/or December and affect most of Europe in March and/or April. Strong influence of synoptic circulation changes is again found in June and August. In general, changes in synoptic circulation has a stronger effect on climate trends in north-western Europe than in the south-east. The exact locations of the strongest influence of synoptic circulation changes vary with the time of year and to some degree between precipitation and temperature. Throughout the year and across the whole of Europe, precipitation and temperature trends are caused by a combination of synoptic circulation changes and within-type changes with their relative influence varying between regions, months and climate variables.
Highlights
The need to understand the influence of global change on the water cycle has led to considerable scientific effort as seen by a number of studies of trends in hydrometeorological variables (IPCC, 2013)
Gridded precipitation and temperature data (1963–2001) originate from the Watch Forcing Data set and synoptic types are defined by the objective SynopVis Grosswetterlagen (SVG)
Throughout the year and across the whole of Europe, precipitation and temperature trends are caused by a combination of synoptic circulation changes and withintype changes with their relative influence varying between regions, months and climate variables
Summary
The need to understand the influence of global change on the water cycle has led to considerable scientific effort as seen by a number of studies of trends in hydrometeorological variables (IPCC, 2013). Large-scale studies covering all of Europe include, for example, Klein Tank et al (2002), Klein Tank and Können (2003), Zolina et al (2010), Teuling et al (2011) and van den Besselaar et al (2012) for precipitation and temperature. These studies cover both annual and seasonal averages as well as extremes and document changes in averages and the structure of European hydroclimatology, including more frequent precipitation extremes and longer wet periods. One example is the work by Serrano et al (1999) who considered monthly precipitation trends on the Iberian Peninsula (1921–1995).
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