One of the roles of geosciences is to provide the society with efficient tools that may diagnose or predict various environmental hazards. Floods are among such events, and hence there is an ongoing need to develop and improve hydrological models. However, especially in mountainous catchments which respond quickly to extreme rainfall, the need covers not only predictive models but also real-time systems that produce and publish up-to-date predictions with sub-hour update frequency. This includes forecasting both the hydrograph and inundation. The objective of the paper is to present a novel approach that integrates the real-time system for forecasting hydrograph, known as HydroProg, with the following two elements: the real-time inundation model that simulates the flood extent on the top of the Digital Elevation Model (DEM), referred to as FloodMap, and the on-demand monitoring of inundation using the Unmanned Aerial Vehicle (UAV). Although skills of the hydrograph prediction models are relatively easy to assess, the problem arises when we want to evaluate the performance of inundation models. This can be done as a near real-time procedure, initiated automatically when the HydroProg and the associated FloodMap produce flood alert, making use of the UAV for oblique photogrammetry. The UAV- taken aerial photographs enable production of orthophoto images which are utilized to check the accuracy of spatial predictions of water extent. The prototype of the comprehensive integrated system is presented, and the results are based on the experimental implementation of the HydroProg system in the upper Nysa Kłodzka River basin (SW Poland).