Integrating High-Temperature Aquifer Thermal Energy Storage (HT-ATES) into District Heating Networks: A Dynamic Multi-Model Scenario Evaluation of Environmental–Economic Impacts

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) offers large-scale, low-cost seasonal heat storage, enabling surplus-heat utilization and improving the environmental performance of district heating networks (DHNs). However, prospective dynamic scenario assessments of integrating HT-ATES into transitioning DHNs are scarce. We evaluate the environmental–economic performance of evolving HT-ATES capacity at three candidate sites in Mannheim’s third-generation DHN as the system transitions toward renewable heat supply. A generalized multi-model framework combines geological subsurface characterization and thermo-hydraulic simulation with dynamic life-cycle assessment and life-cycle costing across future DHN technology configurations and global development pathways. HT-ATES integration is benchmarked against no-integration and evaluated using eco-efficiency metrics. Over 30 years, the best-performing site under a middle-of-the-road pathway achieves net savings of 142 kt CO 2 e, 808 MEUR in avoided external damage costs, and 116 kEUR in internal cost savings. Across scenarios, net savings range from 107 – 395 kt CO 2 e and 644 – 4 441 MEUR in avoided external damage costs, while internal costs range from 0.12 MEUR in savings to a 9.5 MEUR net increase. Site-to-site differences are modest; results are driven primarily by consequential modeling choices and scenario assumptions regarding DHN technologies, energy costs, and background inventories. Economic outcomes are sensitive to discount rate, heat-pump cost and lifetime, and displaced heating technologies. Overall, the case study indicates substantial emission reductions and large avoided external damage costs, but limited economic life-cycle viability for decarbonizing DHNs. While results are network- and scenario specific, the methodology provides a transferable framework for integrated HT-ATES evaluation across subsurface settings and DHNs. • Multi-model framework for multi-impact evaluation of HT-ATES integration into DHNs. • HT-ATES lowers environmental impacts in renewable DHNs despite cost challenges. • HT-ATES can be a cost-effective carbon mitigation option relative to the EU ETS. • Global development pathways drive results more than candidate-site differences. • Key factors are displaced heat supply, heat pump cost/lifetime, and discount rate.