For this study we investigated the Rzyki G watercourse catchment situated in Andrychów District of Wadowice County in the western part of Poland’s Malopolska Region. The basis for the analyses were daily values of precipitation and runoff sums and flow rates in the analyzed watercourse. The empirical data were obtained from systematic precipitation measurement conducted in 1992-2001 by means of a Hellmann rain gauge, and the runoff amounts were determined on the basis of water states registered by limnigraph on a bipartite spillway of a triangle-trapezoid type. The aim of our paper was to assess regularities of selected elements characterizing the hydrological regime of a sub-mountain catchment with dominant agricultural management. The stationarity and variability of monthly precipitation, runoff sums, and runoff coefficients – as well as trends, stationarity, and variability of the flood indicators characterizing maximum stream flows – were analyzed in the paper. Apparent differences appear in cases of variance of the analyzed variables (precipitation variability may be caused by gradual climate warming, whereas higher variability of the runoff in the second half of the multiannual period was determined by precipitation). Due to the changes observed in time series characteristics of the investigated variables, it becomes necessary to analyze the time series not only regarding the occurrence or absence of the trend, as has been done so far, but also considering the other aspects such as the differences between the means or variability of variance. When extreme phenomena are identified at usual lack of a sufficiently long data sequence, the flood rate indicators should be used to comprise much more information than the analysis based only on annual maximum discharge. A significant increase in the annual maximum stream flows was demonstrated for the analyzed multiannual period and for the summer half year, but also higher frequency of flood occurrence in the summer half-year. The observed regularities are typical for the sub-mountain and mountain catchments of the temperate climate and are additionally determined by catchment size.