The existing UFLS schemes suggested for conventional power systems need to be reassessed in the presence of renewable energy sources and storage systems equipped with grid-supporting convertors. A new Event-Based Under-Frequency Inertia Emulation (EB-UFIE) plan is proposed in this paper as a substitute of traditional UFLS program to protect the system against the risk of generation trip and subsequent blackout. Trajectory sensitivities are used as a popular technique to predict the future behavior of the system through a mixed integer programming optimization problem. The proposed scheme has been tested on the modified New England 39-bus system including renewables and storages.