Accurate estimation of coastal hazards requires considering the dependence between extreme wave heights and storm surges particularly in regions affected by typhoons. This study analyzes the joint probability of these variables using approximately 14 years of field observations from Taiwan. An event-based sampling method was adopted, utilizing a new definition of the typhoon influence period to isolate extreme events. The dependence structure was modeled using bivariate copulas with the Gumbel–Hougaard (GH) copula and Generalized Extreme Value (GEV) marginal distributions. These were integrated with a Poisson model to form a Compound Extreme Value Distribution (CEVD). The results indicate that design values derived from joint return periods provide a more realistic assessment of risk compared to univariate methods. Furthermore, a new typhoon-induced coastal hazard classification scheme based on these joint probabilities is proposed, providing a more effective tool for coastal hazard warning and assessment.

Nature-based Solutions (NbS) use natural processes to address social, economic, and environmental challenges, including climate change, and this study explores their application for coastal protection. Before the actual implementation of NbS structures, co-creation with stakeholders to identify and assess potential NbS solutions for the selected local site is essential. However, existing frameworks for selecting NbS measures in coastal protection remain limited in handling the complex interactions among multiple indicators and the inherent uncertainty in expert evaluations. To address this gap, we develop an integrated assessment framework specifically for NbS in coastal protection. We first identified 18 distinct coastal protection measures through literature reviews. The proposed framework combines the Fuzzy Delphi Method (FDM) and entropy-based intuitionistic fuzzy TOPSIS (IF-TOPSIS) to facilitate expert-driven multi-criteria decision analysis (MCDA), both of which use fuzzy theory to address uncertainty and ambiguity in expert judgments. The 18 consensus indicators from an initial pool of 63 evaluation indicators are obtained in FDM analysis. Subsequently, IF-TOPSIS is applied to rank the 18 measures against these evaluation indicators based on membership, non-membership, and hesitancy degrees. The proposed framework is demonstrated through a case study at the Golden Coast, Tainan, Taiwan to illustrate its practical applicability.

The separation of wind sea and swell is crucial for advancing wave dynamics research, improving wave forecasting, and optimizing the design of coastal and offshore structures. In this study, we highlight the limitations of the widely used wave age method for separating two-dimensional wind sea and swell. Specifically, under strong wind conditions, waves require extended durations to reach full development—an aspect not accounted for by the wave age method, which assumes fully developed seas and thus tends to overestimate wind sea. Furthermore, changes in wind direction and wave refraction in shallow waters can lead to misclassification. To overcome these issues, we propose a novel algorithm for directional spectral separation, grounded in wind wave growth theory and incorporating wave refraction effects. The proposed method improves separation accuracy and delivers more consistent results across a range of wave conditions.

Hydro-meteorological risks are a growing issue for societies, economies and environments around the world. An effective, sustainable response to such risks and their future uncertainty requires a paradigm shift in our research and practical efforts. In this respect, Nature-Based Solutions (NBSs) offer the potential to achieve a more effective and flexible response to hydro-meteorological risks while also enhancing human well-being and biodiversity. The present paper describes a new methodology that incorporates stakeholders’ preferences into a multi-criteria analysis framework, as part of a tool for selecting risk mitigation measures. The methodology has been applied to Tamnava river basin in Serbia and Nangang river basin in Taiwan within the EC-funded RECONECT project. The results highlight the importance of involving stakeholders in the early stages of projects in order to achieve successful implementation of NBSs. The methodology can assist decision-makers in formulating desirable benefits and co-benefits and can enable a systematic and transparent NBSs planning process.