An operational coastal forecasting tool for performing ensemble modeling

Abstract

An automated coastal estuarine modeling system, termed Multistage, is created in the ADCIRC hydrodynamic model. The software development was motivated by the need for reducing the simulation wall-clock time to increase the scalability of ADCIRC for ensemble modeling. Multistage makes use of a one-way nesting technique as an alternative to the continuous single-domain approach. Hydrodynamic predictions, such as storm surge and waves, are made for a targeted coastal region in a two-stage scheme consisting of a large-scale coarse mesh simulation and a small-scale fine mesh simulation. The nesting technique is adjusted for accurate and efficient coastal estuarine modeling with careful considerations. We propose and successfully test a method for the coarse mesh extending onshore rather than the common practice of extending the fine mesh offshore. Repetitive ensemble computations are allowed over both the coarse mesh and the fine mesh in an efficient time frame. Modeling preparations and processes are scripted to eliminate the additional efforts needed for applying this model nesting technique. The tool is tested on two coastal estuarine systems, and its performance is compared with the conventional single-domain method and observational data. By implementing Multistage, forecast runtimes are reduced by 50% to more than 80% using the same model parameters and computational resources as used in the conventional single-domain technique. Depending on the domain and model type, it is possible to perform 3-to-5 ensemble simulations on both coarse and fine meshes by applying the nesting technique and using the same amount of CPU-hours needed to complete one single-domain simulation. This research details the concept, preliminary results and offline applications of the tool. Future work is focused on enhancing the ease of use and on development and implementation of a real-time version.