The HYDROSYS project aims to provide a system to support teams of users in on-site monitoring events using handheld devices as a response to some environmental events. Event-driven campaigns provide users the capacity to analyse and predict environmental changes on-site, supporting the process of taking appropriate countermeasures to avoid environmental degradation. The project will make use of both cell phones and handheld computers (ultra mobile personal computers) to reach a large user-base. To analyse the data on-site, the system platform will provide the necessary techniques to deliver the correct data for the location being observed by tracking the users, and also to visualize this data effectively, taking care of the restricted computational resources. The handhelds will access information from advanced sensor technology, managed by a sensor network system that gathers and stores sensor data, and will process model simulations. Two application areas are chosen for validation: pollution caused by storm water and permafrost melting.