Maksymalny czas trwania głębokich niżówek letnich w środkowej Polsce i jego uwarunkowania
Maximum duration of extreme summer Iow flows in central Poland and its determinants

Summary/Abstract: Maximum duration of extreme summer flows in central Poland was estimated on the baseof hydrometric data including twenty four hour flow series from the 1966-1983 period, whichwere published by IMGW. There were 29 water gauges located in Warta, Pilica and Bzuradrainage basins (Fig. l) shortlisted for the analysis. Low flow periods were sectioned basing ona border flow SNQ - a principle was that the period with flows below the borderline hadlasted at least 5 days, while low flows followed in succession had to be divided by periods offlows higher than SNQ being minimum 3 days long.Maximum summer flows were at that time very differentiated and their length fluctuatedfrom 10 to 282 days (Fig. 2). According to that some kind of spatial order can be outlinedhere, the longest low flow periods appeared in Great Poland and Warsaw - Berlin GlacialValley (Fig. 3). Maximum length of low flow was significantly correlated with the parameters,which illustrated flow recession time, mean time of low flow or extreme time constitution intotal low flow and extreme low flow time (Fig. 4, 8).The parameters of maximum length probability distribution were estimated as well. On thebase of those calculations was estimated the probability of not achieving the maximum, whichwas empirically confirmed. Values fluctuated from 90-99.2% usually being about 96% (Fig. 6).The greatest probability of lengthening of maximum low flow periods had Great PolandRivers (Mogilnica, Wrześnica, Lutynia), while the smallest probability was characteristic forrivers, which origins are in uplands (Warta - Poraj, Pilica - Przedbórz).

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