TopoToolbox 3, a laboratory for quantitative geomorphology

Abstract. TopoToolbox has been widely used to analyze and model landscapes across geomorphology and other geospatial disciplines for the past 15 years. Its documentation and accessible interfaces have made it a valuable resource for teaching and learning quantitative geomorphology while its customizability and efficiency have allowed researchers to use it as a platform for experimentation and implementation of their own analyses and models. Its third version, TopoToolbox 3, builds on these developments by improving access to the software, integrating with a larger ecosystem of geomorphology software, and establishing sustainable research software engineering practices. TopoToolbox, previously available only on the MATLAB platform, is now also available to users of Python, and an R interface is under development. The redesigned architecture of TopoToolbox 3 is based on a shared library of core computational routines that makes these and other integrations possible while maintaining the MATLAB interface for existing users of the software. We illustrate the power of this design with examples of how users can integrate TopoToolbox into their workflows. First, we compare the implementation of a basic application, $\chi$ maps, in MATLAB and Python. Second, we use the GraphFlood hydraulic model, now available in TopoToolbox, to showcase the potential of integrating simulation tools and analyzing their output in one computational environment. Third, we demonstrate a two-way coupling between TopoToolbox and the Python-based Landlab landscape evolution modeling framework. Finally, we show how property-based testing can successfully identify bugs in the absence of known solutions to test cases. We conclude by discussing how improved quality assurance and community-driven development practices ensure that TopoToolbox continues to serve the evolving needs of the geomorphology community.