Fig. 4: Contributions of hydroclimatic, geographic and human drivers across sub-basin salinity impact classes.

Distribution of driver levels across sub-basin salinity impact classes, for a selection of 17 out of the total 26 considered driver variables. The selection includes all driver categories (as listed in Table 1), but where multiple variables within the same category exists (e.g., for soil salinity), only one variable was included. The salinity impact classes are based on groups of sub-basins with Low (EC < 700 µS cm⁻¹; green boxplots), Moderate (EC = 700–1500 µS cm⁻¹; yellow boxplots) and High (EC > 1500 µS cm⁻¹; orange boxplots) salinity levels, classified from long-term annual average values (as illustrated in Fig. 2). The selected drivers are plotted along groups of (i) hydroclimatic, (ii) geographic and (iii) human (agricultural-related) drivers on the x-axis, and their normalised levels on the y-axis. The values were normalised by dividing each sub-basin specific driver value by the group-average value, for each driver and then grouped over each salinity impact class. Full driver names and original units are given in Table 1. Boxplot statistics include the median (vertical thick black lines), interquartile range (IQR: 25th percentile; Q1 and 75th percentile; Q3) and whiskers (confidence interval of Q1 − 1.5∗IQR to Q3 + 1.5∗IQR). The stars (*) over the boxplots indicate where there are statistically significant differences in the driver contributions between the Low-High salinity impact classes (all summary statistics are included in Supplementary Table 1).