Hierarchical Multi-Agent Reinforcement Learning for Cooperative Wildfire Suppression with Amphibious Firefighting UAVs

Cooperative task planning for amphibious firefighting UAVs deployed across multiple bases is challenging because of complex resource coupling, evolving fire conditions, and real-time decision requirements. This study proposes an H-MAPPO-LSTM method with a three-level hierarchical multi-agent structure: a Command-Center Agent performs global situation assessment and macroscopic task allocation, Base Agents manage UAV resources and decompose regional tasks, and UAV Agents execute water collection, flight, water-dropping, and return operations. LSTM networks are incorporated into the policy networks and combined with PPO and centralized training with decentralized execution to enable multilevel cooperative learning and online dynamic replanning. During deployment, network parameters remain fixed, while online policy inference, real-time decision-making, and dynamic replanning respond to fire-scene changes. The model jointly considers UAV bases, amphibious firefighting UAVs, natural water sources, dynamic fire hotspots, and their constraints. Compared with Flat MAPPO in the static benchmark, H-MAPPO-LSTM reduces mission completion time by 20.2%, average response time by 14.7%, final burned area by 29.7%, and comprehensive cost by 26.0%. Fire-containment rates reach 88% in highly dynamic scenarios and 81.96% in large-scale scenarios. Ablation results indicate that the hierarchical architecture provides the most pronounced contribution under the tested settings, while LSTM, the level-specific centralized critics, and hierarchical rewards provide additional performance contributions under the tested settings.