The proliferation of Internet of Things (IoT) applications and real-time services brings severe performance pressure on IoT systems with cloud computing, so edge computing is increasingly being adopted in IoT systems to assist cloud computing in providing services. Systems with cloud-edge computing deploy parts of services on edge servers located closer to IoT devices, thus enabling real-time data processing and analysis and improving the quality of experience (QoE) of users. However, inevitable extreme events (e.g. meteorological disasters) and the aging of the physical infrastructure cause varying degrees of performance impairment to edge servers, which adversely affects the service provisioning capability of IoT systems. Therefore, there is a serious challenge to cope with the lack of service provisioning capability owing to the impaired edge server performance in extreme environments. In this paper, an unmanned aerial vehicle (UAV) -assisted service provisioning framework for the IoT systems in cloud-edge computing is introduced, and a UAV-enhanced service caching scheme based on a potential game (G-USC) is proposed for this framework. Besides, to provide a prerequisite for service caching, a UAV position update scheme based on a deep Q-network is designed. The experimental analysis proves that G-USC effectively solves the problem of insufficient service provisioning capability of edge servers in extreme environments.