GIS-Based Spatial Assessment of Co-Located Solar–Green Hydrogen and Industrial Wastewater Reuse Systems: A Case Study of Karachi

Urban–industrial regions in the Global South face intertwined challenges of energy insecurity, freshwater scarcity, and environmental degradation that are strongly shaped by spatial context. This article presents a Geographic Information Systems (GIS) informed case study examining the integration of a solar–green hydrogen hybrid energy system with industrial wastewater reuse at a textile manufacturing facility in Karachi, Pakistan, a water-stressed and solar-rich megacity with concentrated industrial activity. Designed for sustainability science and GIS education, the case demonstrates how spatial analysis can inform real-world decision-making at the water–energy nexus. Using a transparent and replicable GIS workflow, the study integrates spatial datasets on solar resource availability, industrial land use, wastewater generation, and infrastructure proximity to evaluate the feasibility and sustainability implications of co-locating renewable energy generation, hydrogen storage, and wastewater treatment within an industrial zone. Results show that spatially integrated deployment improves energy reliability, substantially reduces freshwater withdrawal through wastewater reuse and water recovery, and delivers environmental benefits by displacing fossil-fuel-based electricity in dense industrial areas. The analysis further demonstrates that these benefits are highly location-dependent and diminish in settings where energy demand and wastewater availability do not spatially overlap. Through this case, readers will learn how GIS can be applied to evaluate integrated energy–water systems, assess spatial trade-offs, and develop place-based sustainability strategies applicable to other urban–industrial contexts.