Accessible Batch Catchment Delineation: A Semi-Automated Workflow for Non-Hydrologists

Catchment delineation is a prerequisite for hydrological and water-quality analyses but remains a practical barrier for non-hydrologists, particularly when large numbers of sites must be processed. We present here a semi-automated, reproducible workflow for batch catchment delineation using openly available GIS tools. The workflow was developed during delineation of 2,870 monitoring sites assessed for the EU Water Framework Directive and evaluated in a 25-site case study in southern Spain. We compare delineations derived from multiple global Digital Elevation Models (DEMs) and assess their congruency with official catchment boundaries using Jaccard similarity. Results show that 1 arcsec DEMs, particularly FABDEM and Copernicus GLO-30, provide the most accurate and consistent delineations, while coarser products show larger variability. We identify recurring failure modes related to infrastructure, artificial drainage, reservoirs and endorheic basins, and propose low-effort quality-control steps. The workflow enables reliable large-scale catchment delineation for research, management and planning with minimal hydrological expertise.