Attribution of European precipitation and temperature trends to changes in circulation types
Hydrology and Earth System Sciences Discussions, 11 (11):
12799--12831 (Nov 18, 2014)DOI: 10.5194/hessd-11-12799-2014
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 atmospheric circulation. The relative importance of circulation changes (i.e. trends in circulation type frequencies) as opposed to trends in the hydrothermal properties of circulation types (within-type trends) on precipitation and temperature trends in Europe is assessed on a monthly basis. Gridded precipitation and temperature data originate from the Watch Forcing Dataset and circulation types (CTs) are defined by the objective SynopVis Grosswetterlagen. Relatively high influence of circulation changes are found from January to March, contributing to wetting trends in northern Europe and drying in the South. Simultaneously, in particular dry CTs get warmer first in south-western Europe in November/December and affecting most of Europe in March/April. Strong influence of circulation changes is again found in June and August. In general, circulation influence affects climate trends in north-western Europe stronger than the South-East. The exact locations of the strongest influence of circulation changes vary with time of the 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 circulation changes and within-type changes with their relative influence varying between regions, months and climate variables.