Swiss water quality: extending CAMELS-CH with data on isotopes, water quality and atmospheric chemistry

In the era of large-sample hydrology (LSH), there is still a lack in the availability of consistent data related to water quality. To address this gap, we introduce CAMELS-CH-Chem, a dataset inspired by the recently published CAMELS-Chem for the contiguous United States. CAMELS-CH-Chem extends CAMELS-CH (Catchment Attributes and Meteorology for Large-sample Studies in Switzerland) by integrating stream water chemical parameters and atmospheric deposition data for 115 monitoring stations across Switzerland. Spanning the same period as the CAMELS-CH 1981–2020, with consistent identifiers, it enables seamless integration with the original hydro-meteorological and landscape attribute data. The dataset primarily encompasses data from the Swiss Federal Office for the Environment. It includes time series of over 20 stream water chemistry constituents, covering both field and laboratory data on water temperature, dissolved oxygen, pH, and electrical conductivity both at hourly and daily time resolution; together with measurements of alkalinity, ammonium, Ca, Cl, dissolved organic carbon (DOC), dissolved reactive phosphorus (DRP), total organic carbon (TOC), HCO₃, K, Mg, Na, total hardness,  total dissolved nitrogen, total organic nitrogen, total phosphorus, NO₃, NO₂, Si, and SO₄. The dataset also includes monthly time-series of stream isotope data (deuterium and oxygen-18), annual atmospheric deposition concentrations for NO₃, NH₄, NH₃, NO₂ and total inorganic nitrogen, and aggregated livestock density information. Switzerland, often referred to as the 'water tower of Europe,' offers a uniquely diverse setting for hydrological research, characterized by its varied climatic, topographic, and anthropogenic influences. This diversity, combined with the rapid changes driven by climate change, makes Swiss catchments and landscapes an interesting natural laboratory for studying evolving water systems. CAMELS-CH-Chem offers the opportunity to combine an extensive catchment characteristics and streamflow dataset with a detailed set of water quality parameters, facilitating new advances for LSH research. By providing the chance to enhance process-based understanding of the water cycle, this dataset supports studies that integrate both quantity and quality aspects of hydrological systems. To our knowledge, CAMELS-CH-Chem is only the second CAMELS dataset to incorporate such an extension. We anticipate that its release will inspire the development of similar datasets worldwide.