Temporal and spatial variability of precipitation in Sweden and its link with the large-scale atmospheric circulation

The main characteristics of spatial and temporal variability of the precipi tation regime in Sweden were studied by using the long-term monthly precipi tation amount (1800-1990) at 33 stations. The data were filtered by using E mpirical Orthogonal Function (TOT) analysis, which provides principal modes of both spatial variability and time coefficient series describing the dom inant temporal variability. Canonical correlation analysis (CCA) was used t o reveal association between the atmospheric circulation and the characteri stics of the climate variability. Statistically significant upward shifts i n the mean precipitation have been found during cold months (March, Septemb er, November and December) and only a downward shift (less significant) for August. Simultaneous changes in the time series associated to the optimall y correlated circulation patterns were found, indicating an important role of the circulation. The circulation patterns are given by the North Atlanti c Oscillation (NAO) in March and December and a cyclonic structure centred over southern Scandinavia in September and November. These changes may have induced changes in the mean precipitation seasonality reflected by a shift of the maximum precipitation from August to July (after 1931 for western p ;irt and alter 1961 for the southeastern coast) and after 1961 to September , October or November for other regions. Combining rotated EOF analysis wit h cluster analysis, 4 regions with similar climate variability were objecti vely identified. For these regions the standardised monthly precipitation a nomalies were computed. The frequency of the extreme events (very dry;wet a nd dry/wet months) over 5-year consecutive intervals was analysed. It has b een concluded that extreme wet months were more frequent than extreme dry m onths over the entire country, especially in the northern and southeastern part.