  In this paper, we address the issue of congestion in future Unmanned Aerial
Vehicle (UAVs) traffic system in uncertain weather. We treat the traffic of
UAVs as fluid queues, and introduce models for traffic dynamics at three basic
traffic components: single link, tandem link, and merge link. The impact of
weather uncertainty is captured as fluctuation of the saturation rate of fluid
queue discharge (capacity). The uncertainty is assumed to follow a
continuous-time Markov process. We define the resilience of the UAV traffic
system as the long-run stability of the traffic queues and the optimal
throughput strategy under uncertainties. We derive the necessary and sufficient
conditions for the stabilities of the traffic queues in the three basic traffic
components. Both conditions can be easily verified in practiceB. The optimal
throughput can be calculated via the stability conditions. Our results offer
strong insight and tool for designing flows in the UAV traffic system that is
resilient against weather uncertainty.
