delineator

delineator, by Matthew Heberger, is the open Python engine that powers the Global Watersheds web app: give it outlet coordinates and it returns the upstream catchment, using a hybrid approach — pre-computed MERIT-Basins unit catchments for the bulk of the area, with raster-level MERIT-Hydro refinement only around the outlet — which is why it delineates anywhere on earth in about a second.

Run it yourself when you need batch delineation (hundreds of gauging stations, say) or want the workflow inside your own pipeline rather than a browser. Accuracy inherits the ~90 m global hydrography, so it screens and scopes rather than replaces site-specific delineation from lidar.