The aim of the study was to compare two grouping methods for regionalisation of watersheds, which are similar in respect of low flow and chosen catchments parameters (physiographic and meteorological). In the study, a residual pattern approach and cluster analysis, i.e. Ward’s method, were used. The analysis was conducted for specific low flow discharge q95 (dm3∙s–1∙km–2). In the analysis, 50 catchments, located in the area of the upper and central Vistula River basin, were taken. Daily flows used in the study were monitored from 1976 to 2016. Based on the residual pattern approach (RPA) method, the analysed catchments were classified into two groups, while using the cluster analysis method (Ward’s method) – into five. The predictive performance of the complete regional regression model checked by cross-validation R2cv was 47% and RMSEcv = 0.69 dm3∙s–1∙km–2. The cross validation procedure for the cluster analysis gives a predictive performance equal to 33% and RMSEcv = 0.81 dm3∙s–1∙km–2. Comparing both methods, based on the cross-validated coefficient of determination (R2cv), it was found that the residual pattern approach had a better fit between predicted and observed values. The analysis also showed, that in case of both methods, an overestimation of specific low flow discharge q95 was observed. For the cross-validation method and the RPA method, the PBIAS was –10%. A slightly higher value was obtained for the cross-validation method and models obtained using cluster analysis for which the PBIAS was –13.8%.

The purpose of the paper is to analyze the spatial variability of precipitation in Poland in the years 1981–2010. The av-erage annual rainfall was 607 mm. Precipitation in Poland is characterized by high spatial and temporal variability. The lowest annual precipitation was recorded in the central part of the country, where they equaled 500 mm. The highest annual precipitation totals were determined in the south, equaling 970 mm. The average precipitation in the summer half-year is 382 mm (63% of the annual total). On the basis of data from 53 climate stations, maps were made of the spatial distribution of precipitation for the period of the year and winter and summer half-year. The kriging method was used to map rainfall distribution in Poland. In the case study, cross-validation was used to compare the prediction performances of three periods. Kriging, with exponential type of semivariogram, gave the best performance in the statistical sense. Their application is justices especially in areas where landform is very complex. In accordance with the assumptions, the mean prediction error (ME), mean standardized prediction error (MSE), and root mean-square standardized prediction error (RMSSE) values are approximately zero, and root-mean-square prediction error (RMSE) and average standard error (ASE) reach values well below 100.