PHALK - A global dataset of estimated pH and alkalinity in inland waters at basin-scale

This dataset contains pH and alkalinity values for surface waters within HydroBASINS polygons, estimated worldwide, as well as pH and alkalinity measured values at sites used for model construction, along with the associated predictor variables obtained for this project. We provide a global compilation of alkalinity and pH values from inland surface waters (rivers, lakes/reservoirs, and wetlands) collected from 18 databases and 55 scientific articles. We based our approach on the procedure outlined by Virro et al. (2021) for harmonizing the hydrochemical data. After performing accurate quality control filtering, we constructed a dataset comprising data from 50,916 sites for alkalinity and 107,896 for pH distributed across continents. This dataset allowed us to model the inland water pH and alkalinity at the basin scale with a random forest model and 23 variables related to the catchment morphology, environmental basin characteristics, and the lithological composition of the bedrock, coming from the HydroSHEDS project (Lehner et al. 2008) and The Global Lithological Map GLiM (Hartmann & Moosdorf 2012). The basins used were those provided by the vectorial dataset of HydroBASINS and constitute the model reference units. All methodological details are available in Batalla et al. (2026). The uncertainty associated with the model was quantified using the coefficient of variation of the estimated pH and alkalinity values across the 200 bootstrap random forest trees, as well as the environmental differentiation of each basin relative to the pH and alkalinity training dataset. • Batalla M, Martínez-Artero J, Catalan J. (2026). Global basin-scale mapping of pH and alkalinity in inland waters. Scientific Data submitted, • Hartmann, J., Moosdorf, N. (2012). The new global lithological map database GLiM: A representation of rock properties at the Earth surface. Geochemistry, Geophysics, Geosystems, 13, Q12004. https://doi.org/10.1029/2012GC004370 • Lehner, B., Verdin, K., Jarvis, A. (2008). New global hydrography derived from spaceborne elevation data. Eos, Transactions, American Geophysical Union, 89(10): 93–94. https://doi.org/10.1029/2008eo100001 • Virro, H., Amatulli, G., Kmoch, A., Shen, L. & Uuemaa, E. GRQA: Global River Water Quality Archive. Earth Syst. Sci. Data 13, 5483–5507 (2021). https://doi.org/10.5194/essd-13-5483-2021