Application of optical flow technique to short-term rainfall forecast for some synoptic patterns in Vietnam

Abstract

Abstract The occurrence of heavy rains can lead to human, economic, and ecological disasters with large-scale consequences. There are now many precipitation forecasting systems that use radar products with different algorithms and techniques to provide forecasts for up to one to three hours, such as McGill algorithm for precipitation nowcasting by Lagrange extrapolation (MAPLE), Short-Term Ensemble Prediction System (STEPS), and Short-range Warning of Intense Rainstorms in Localized Systems (SWIRLS). Optical flow engineering is an important technique in computer vision. Our aim was to apply optical flow techniques using the methods of DenseRotation_FCAFlow - this method is a small branch of the Rainymotion library system, belonging to the Dense method group DenseRotation_Farneback - this method uses the local optical flow and polynomial function extension techniques to calculate radar echo region motion, Real-time Optical Flow by Variational Methods for Echoes of Radar - this method is used with two sets of parameters for Hong Kong (ROVER_HKO) and Vietnam ( ROVER_VN) to predict rainfall quantitatively from 2019–2021 radar rainfall quantitative data in Vietnam. The results show the following: (i) Changing the parameterizations of the ROVER_HKO method to apply to conditions in Vietnam (ROVER_VN) gives better results than the remaining methods for the total accumulated rainfall of the entire rainfall events, and the ROVER_VN method gives the best results in case rain occurs due to a combination of many synoptic patterns; (ii) The performance of Quantitative Precipitation Forecasting (QPF) using a performance diagram with light and moderate rainfall thresholds is also better captured in a combined local and global optical flow method than when using either type of optical flow alone. The ROVER_VN method quantitatively forecasts the cumulative rainfall of the entire rain event in case the rain is caused by the interaction of many different synoptic patterns and the rainfall area develops to be wide and fast moving, playing an especially important role in providing input data for forecasting and warning of floods, flash floods, and landslides throughout the territory of Vietnam.