Abstract
In this paper, we quantify the changes in precipitation distribution in south-western Poland between the periods 1891–1930 and 1981–2010. The average monthly precipitation totals available for 368 and 245 stations, respectively, are spatially interpolated and processed to calculate maps of differences and pluvial continentality indices for both periods. The maps are analysed against changes in atmospheric circulation and take into account the potential role of the mountain barrier of the Sudetes. The main findings are (1) winter totals generally increased in conjunction with a higher frequency of zonal circulation; it is more pronounced in the upper parts of the Sudetes due to orographic effects; (2) a decreased frequency of zonal circulation together with an increased frequency of southern flows has likely led to the reduction of precipitation in spring and autumn. These changes have led to a significant modification of the region’s pluvial regime, mostly by decreasing continentality features (especially in the Sudetes and the western lowlands). In addition, the strong sheltering influence of the mountain barrier is observed, driving the preservation or even the enhancement of the continental pluvial characteristics in the north-eastern to eastern foregrounds of the Sudetes. This leads to the conclusion that in areas where long-term observed trends or future projections of precipitation are ambiguous, there may occur significant modifications in regional characteristics, especially as a result of changes in atmospheric circulation modified by local orography.
Highlights
Atmospheric precipitation is one of the key elements of the hydrological cycle
Mean annual sums are very similar in both stations: 576.8 mm in Wrocław and 577.2 mm in Cottbus, and no significant trend in annual totals has been observed in each station (Table 1)
Full statistical analysis of the correlation between atmospheric precipitation and circulation is beyond the scope of this paper
Summary
Atmospheric precipitation is one of the key elements of the hydrological cycle. It plays a vital role in all natural ecosystems and many human-environment sectors including agriculture, forestry, energy production, water supply and many others. Mean annual precipitation trends since the 1950s show an increase by up to 70 mm per decade in North-eastern and North-western Europe and a decrease by up to 70 mm in some parts of Southern Europe. Seasonal trends show an increase in winter precipitation in Northern Europe and a decrease in Southern Europe, but with large interannual variations (EEA 2012). Similar tendencies are projected to continue in the future, with less clear trends in annual totals in Central Europe, an increase in Northern and a decrease in Southern Europe. Climate projections show a precipitation decrease for the summer months and an increase in winter (Schmidli et al 2007)
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