It is increasingly popular to use unmanned air vehicle (UAV) and network model to detect targets and gather information in water resources, environment and hydraulic engineering field. The intermittent connectivity in a dynamically mobile UAV network (UAVN) makes it challenging to efficiently gather sensed target data. Centralized and distributed fusion rules in traditional fusion systems are often based on global message connectivity. This paper investigates the severe communication of sensed data from a set of mobile survey UAVs to a fusion center in large outdoor environment. Then a centralized fusion model for UAVN is proposed to schedule the UAVs to collect detection data to solve water problems with the dynamic connectivity of links in UAV network. Based on this model, a specific fusion method named Capacity Fusion Rule (C-FR) is provided for the fusion center. C-FR utilizes the information theory to discuss the fusion performance in view of link connectivity. Evaluation shows that the proposed C-FR can realize the centralized fusion system with simpler formulas and express the numerical relationship between outage probability, outage capacity, and connectivity probability. Otherwise, computational complexity of traditional centralized fusion rule and C-FR are also analyzed.