CR 56:245-259 (2013)  -  DOI: https://doi.org/10.3354/cr01155

ABSTRACT: The principal aim of the research was to describe the summer variability of extreme daily precipitation totals in Poland and to identify and quantify its relation to regional atmospheric circulation. The case of extreme precipitation was defined as a day with a daily precipitation total above the value of the long-term 90th percentile of daily precipitation totals (on a monthly scale). Spatio-temporal variability of extreme precipitation occurrences was investigated with the aid of eigentechniques, while identification of the relationship between regional forcing (atmospheric circulation) and local response (extreme daily precipitation occurrence) was attempted via redundancy analysis (RDA). The downscaling model was constructed on the basis of the 1971-1990 period and its verification comprised the periods 1961-1970 and 1991-2008. The variance of the local response to regional forcing explained by the RDA model exceeds 70% in the case of individual months and is nearly 60% in case of the whole summer season. However, the high number of identified empirical orthogonal functions (EOFs) suggests significant influence of local conditions on the spatial variability of extreme rainfall. Relatively high values of redundancy index (50 to 60%) also show that for individual months the variability of the sea level pressure (SLP) over the Euro-Atlantic region determines a substantial share of extreme rainfall. However, unsatisfactory results of model verification also imply that the connections established by the model might not be stationary, and that a longer period should be used in the model calibration process.

KEY WORDS: Precipitation extremes · Downscaling · Climate extremes