| 20 Feb 2026
Rating Surfaces for Quantifying Compound Flooding at Points of Interest
Abstract. Compound flooding in low-relief coastal regions arises from interactions among coastal water levels, river discharge, and precipitation. Capturing these interactions typically requires coupled hydrodynamic models, which can be computationally intensive, limiting their use in high-resolution or large-ensemble analyses. In this study, we introduce rating surfaces: two-dimensional plots that provide contours of compound flood depth at points of interest given pairs of potentially interacting flood drivers. Using Southeast Texas as a testbed, we generate synthetic inundation scenarios with both efficient terrain-based models (c-HAND, GeoFlood, and Fill-Spill-Merge) and the reduced-physics hydrodynamic model SFINCS. Sampling these scenarios at points of interest yields rating surfaces that characterize how precipitation, discharge, and coastal water level jointly influence maximum compound flood depth. Across locations, simplified and hydrodynamic models produce similar depth patterns, but SFINCS captures finer-scale nonlinearities. The two approaches provide comparable depth estimates, and their prediction envelope typically includes the observed high-water marks. Rating surfaces provide an efficient tool for evaluating compound flooding in settings where computational constraints challenge traditional hydrodynamic modeling, offering a framework for scenario assessment and communication of compound flood hazards at points of interest.
The manuscript presents an interesting and well-structured framework for estimating compound flood depth at points of interest using rating surfaces derived from both simplified conceptual-geomorphic models (c-HAND, GeoFlood, and Fill-Spill-Merge) and the reduced-physics hydrodynamic model SFINCS. The approach is computationally efficient and potentially valuable for large-scale or scenario-based analyses. The manuscript is generally sound and suitable for publication after minor revisions addressing the following points:
The manuscript employs simplified conceptual-geomorphic modelling frameworks. While this approach is appropriate for low-relief coastal environments, it is important to clarify that DEM-based HAND-based methods are fundamentally geomorphic and proximity-based approaches, originally designed to delineate flood-prone areas rather than to accurately compute flood depths.
In its current form, the manuscript may suggest that those models provides physically robust estimates of inundation depth. However, HAND-derived methods rely on static topographic relationships (height above nearest drainage) and do not explicitly represent hydraulic processes such as momentum, backwater effects, or flow dynamics. As also indirectly acknowledged in the discussion (e.g., overestimation issues in low-relief areas and segment catchment artifacts) , this can lead to systematic biases in depth estimation, particularly in complex compound flooding conditions.
While several limitations are discussed throughout the manuscript (e.g., DEM accuracy, hydrography completeness, and HAND-related biases), these are currently dispersed across the discussion section. Given the methodological implications outlined above, the manuscript would benefit from a dedicated “Limitations” section that systematically addresses:
This addition would significantly improve transparency and help readers correctly interpret the applicability domain of the proposed framework. I may also suggest that the conclusion section is not a real value, may be you can remove it or merge the limitation and conclusion section into one new sub-section