Figure 1: Schematic overview of the main steps for creating the freshwater variables and the GRASS GIS¹⁴ functions used.

First the vectorised HydroSHEDS¹² stream network was transformed into grids and the stream order computed, and this layer was used to recondition the Digital Elevation Model¹² (DEM). The corrected DEM was then used to calculate the flow direction and to delineate the upstream sub-catchment for each cell along the stream network. Various metrics (min, max, range, average, sum, weighted average and weighted sum) were extracted as text-files from existing climate⁶, topography¹², land cover⁸, surface geology²⁰, and soil²¹ data sets, where each text-file contained the different metrics of a given variable. Once all catchments were processed, the text-files were merged and reclassified into a spatial grid, representing continuous upstream variables. Finally, lakes and reservoirs were extracted from the 1 km gridded Global Lakes and Wetlands Database¹³ and the variables were averaged across each single lake and reservoir entity that intersected with the stream network.