Promoting advances in hydrological modeling through development of the open-source water quality modelling system RSPARROW

The USGS SPARROW (SPAtially Referenced Regressions on Watershed attributes) model is a spatially explicit, statistical and mechanistic water quality model that has been used by researchers and water-resource managers to quantify the sources and environmental controls on transport of contaminants in watersheds from catchment to continental scales. SPARROW is a data-driven model that applies non-linear least squares methods with stream monitoring and geospatial data to predict contaminant transport and loads through a network of one-dimensional stream segments and associated contributing drainage areas. Mechanistic features include mass balance constraints and non-conservative transport components. While SPARROW has proven to be an informative water-quality assessment tool, its reliance on proprietary SAS software limits both the accessibility of the tool for researchers and managers, and the potential for future user-developed innovations. Therefore, the open-source USGS RSPARROW system was developed to broaden the community of SPARROW users and to encourage collaborative development of new model capabilities by removing dependence on proprietary software, improving ease-of-use, and expanding model diagnostic capabilities. RSPARROW is a fully open-source system of scripts and subroutines written in the R programming language that can be used to execute SPARROW models and evaluate results through graphics, maps, tabular files, and interactive tools. A decision support tool, constructed as a Shiny Application, allows users to interactively execute contaminant source reduction scenarios generating stream and catchment maps as well as tabular output data on-the-fly through an easy-to-use push-button interface making execution of source reduction scenarios accessible to both researchers and managers. The RSPARROW standardized methods of storage, maintenance, documentation and retrieval through a GitHub repository promotes further development of a sharable system of SPARROW methods and functionality. By expanding opportunities for both community involvement and innovation in SPARROW model development, the RSPARROW system could potentially contribute to advances in the methods for hydrological models and data integration and techniques for the visualization of model outcomes.