Fig 1.
The spatial distribution of the selected 40 cross-sections (red triangles) amongst all cross-sections (grey triangles) across Poland from the IMGW-PIB database; the triangle size reflects the catchment area and the histograms of the catchment area within individual classes: a) grey–all stations (Aall), b) red–selected stations (Asel). Blue points on the maps show the locations of the nearest synoptic stations assigned to the cross-sections selected for the study.
Fig 2.
The selected cross-sections (red triangles) and all cross-sections (grey triangles); the triangle size reflects the cross-section’s altitude.
The numbers on the maps at the red triangles correspond with the numbers of the gauging stations listed Table A1 in S1 Appendix. The histograms of the altitude (grey and red–all and selected cross-sections, respectively) show that the higher-elevated cross-sections dominate among the selected ones. The hypsometric map (DEM) is available at: https://www.geoportal.gov.pl/pl/usluga/uslugi-przegladania-wms-i-wmts (accessed on 3 April 2024).
Fig 3.
The characteristics (location, area, and altitude) of the 5 gauging stations with the longest sequences and at least one day with an ice phenomenon per year within the study period selected from the complete study period (1951–2021).
Blue circles on the map show the location of the synoptic stations.
Table 1.
The gauging stations with the longest sequences with at least one day with an ice phenomenon per year within the study period.
Fig 4.
The spatial distribution of the gauging cross-sections and the histogram of Nmean—The mean number of days with ice per year (1992–2021).
The colours on the map correspond with the colours in the histogram.
Table 2.
The results of the trend analysis; ZMK is the test statistic of the Mann-Kendall test, asterisk ↓ shows a downward trend, and ▪—No trend.
Table 3.
The number of gauging cross-sections where a statistically significant decreasing trend was identified.
The percentage refers to the datasets in Table 2.
Fig 5.
The Theil-Sen slope estimator for the series of length (a) 30 years, (b) 35 years, and (c) 40 years where the trend was detected.
The vertical lines (in the box) denote from the left: Quantile 25%, median, and quantile 75%; the asterisks represent the mean values.
Fig 6.
The values of the Theil-Sen estimator for the series of lengths (a) 30 years, (b) 35 years, and (c) 40 years.
The triangles’ sharp points indicate the downward trends while grey circles show cross sections with no trend. The strengths of the trend (Theil-Sen slope values) are reflected in the triangles’ colors and can be identified in the histograms on the right side. Grey points show the location of the synoptic stations.
Fig 7.
The time series plots of the number of days with ice (red lines) and mean annual temperature (blue lines) for the series longer than 50 years.
The p-values of the MK test, the index number of days with ice, are denoted by . The red regression lines have slope values equal to the Theil-Sen slopes.