To mark the 20th anniversary of Natural Hazards and Earth System Sciences (NHESS), an interdisciplinary and international journal dedicated to the public discussion and open-access publication of high-quality studies and original research on natural hazards and their consequences, we highlight 11 key publications covering major subject areas of NHESS that stood out within the past 20 years.

Flood risk management requires a realistic estimation of flood losses. However, the capacity of available flood damage models to depict real damages is questionable. With a joint effort of eight research groups, the objective of this study was to compare the performances of nine models for the estimation of flood damage to buildings. The comparison provided more objective insights on the transferability of the models and on the reliability of their estimations.

INSYDE is a multivariable synthetic model for flood damage assessment of dwellings. The analysis and use of this model highlighted some weaknesses, linked to its complexity, that can undermine its usability and correct implementation. This study proposes a simplified version of INSYDE which maintains its multivariable and synthetic nature but has simpler mathematical formulations permitting an easier use and a direct analysis of the relation between damage and its explanatory variables.

The paper presents AGRIDE-c: a conceptual model for the estimation of flood damage to crops. The model estimates both the physical damage on the plants and its economic consequences on the income of the farmers. This allows AGRIDE-c to support effective damage mitigation strategies, at both public and individual farmer levels. The model can be adapted to different geographical and economic contexts, as exemplified by its implementation for the context of northern Italy.

Flood risk management relies on assessments performed using flood loss models of different complexities. We compared the performances of expert-based and empirical damage models on three major flood events in northern Italy. Our findings suggest that multivariate models have better potential to provide reliable damage estimates if extensive ancillary characterisation data are available. Expert-based approaches are better suited for transferability compared to empirically based approaches.

One common approach to cope with floods is the implementation of structural flood protection measures, such as levees. Numerous scholars have problematized this approach and shown that increasing levels of flood protection can generate a false sense of security and attract more people to the risky areas. We briefly review the literature on this topic and then propose a research agenda to explore the unintended consequences of structural flood protection.

By analyzing a comprehensive loss dataset of affected private households after a recent river flood event in northern Italy, we tackle the problem of flood damage estimation in Emilia-Romagna (Italy). We develop empirical uni- and multivariable loss models for the residential sector. Outcomes highlight that the latter seem to outperform the former and, in addition, results show a higher accuracy of univariable models based on local data compared to literature ones derived for different contexts.

Flood risk estimates are characterised by significant uncertainties; accordingly, evaluating the reliability of such estimates (i.e. validating flood risk models) is crucial. Here, we discuss the state of art of flood risk models validation with the aim of identifying policy and research recommendations towards promoting more common practice of validation. The main conclusions from this review can be summarised as the need of higher quality data to perform validation and of benchmark solutions.

This paper presents a model to develop multipurpose complete event scenarios, which address all the needs that arise after a disaster. In detail, such scenarios (i) are multisectoral, (ii) address the spatial scales relevant for the event at stake, (iii) consider the temporal evolution of damage and (iv) allow damage mechanisms to be understood. The model allows flood mitigation strategies to be optimized, as proved by its use in a case study.

INSYDE is a new synthetic flood damage model based on a component-by-component analysis of physical damage to buildings. The damage functions are designed using an expert-based approach with the support of existing scientific and technical literature, loss adjustment studies, and damage surveys. The model structure is designed to be transparent and flexible, and therefore it can be applied in different geographical contexts.

Can differential land-subsidence significantly alter river flooding dynamics, and thus flood risk in flood prone areas? In the area around Ravenna, in Italy, that experimented a cumulative drop of more than 1.5 m after World War II due to groundwater pumping and gas production platforms, we compared the actual effects on flood-hazard dynamics of differential land-subsidence relative to those associated with other man-made topographic alterations, which proved to be much more significant.

The growing concern about the possible effects of climate change on flood frequency regime is leading Authorities to review reference procedures for design flood estimation. Our study focuses on Triveneto (Italy) and proposes an update of the existing reference procedure by properly considering climate and scale controls on flood frequency. Moreover, the study highlights the remarkable influence of a single extreme-floods year on analyses for detecting possible changes in flood frequency regime.

Our study proposes simplified graphical tools (Hypsometric Vulnerability Curves) for assessing the recent dynamics of the flood vulnerability and risk over a large floodable area along the River Po, Northern Italy, and for defining sustainable flood-risk mitigation strategies. We assess the accuracy of the proposed methodology, based on inundation scenarios simulated with a quasi-2D model, by means of a comparison with a traditional approach relying on the simulations of a to a fully-2D model.