Recent advances in wireless communications technology and microelectromechanical systems have enabled the development of low cost, low power, network-enabled, and multifunctional microsensors. Due to their ease of deployment, reliability, scalability, flexibility, and self-organization, the existing and potential applications of wireless sensor networks (WSNs) span a wide spectrum in various domains, the environmental and technical requirements of which may differ significantly. The purpose of deploying a WSN is to collect relevant data for processing and reporting. In particular, based on data reporting, WSNs can be classified as time-driven or event-driven. In this paper, we propose a hybrid data-gathering protocol that dynamically switches between the event-driven data-reporting and time-driven data-reporting schemes. The novel aspect of our approach is that sensor nodes that seem to detect an event of interest in the near future, as well as those nodes detecting the event, become engaged in the time-driven data-reporting process. This capability enables data from neighboring areas to be gathered proactively without requiring observer intervention. As such, the proposed protocol accurately analyzes the environment being monitored using only moderate resource consumption. We have implemented the proposed protocol on a network simulator and analyzed its behaviors using synthetic environments that model the occurrence of a fire.