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Nature-based solutions (NBS) for hydro-meteorological risks (HMRs) reduction and management are becoming increasingly popular, but challenges such as the lack of well-recognised standard methodologies to evaluate their performance and upscale their implementation remain. We systematically evaluate the current state-of-the art on the models and tools that are utilised for the optimum allocation, design and efficiency evaluation of NBS for five HMRs (flooding, droughts, heatwaves, landslides, and storm surges and coastal erosion). We found that methods to assess the complex issue of NBS efficiency and cost-benefits analysis are still in the development stage and they have only been implemented through the methodologies developed for other purposes such as fluid dynamics models in micro and catchment scale contexts. Of the reviewed numerical models and tools MIKE-SHE, SWMM (for floods), ParFlow-TREES, ACRU, SIMGRO (for droughts), WRF, ENVI-met (for heatwaves), FUNWAVE-TVD, BROOK90 (for landslides), TELEMAC and ADCIRC (for storm surges) are more flexible to evaluate the performance and effectiveness of specific NBS such as wetlands, ponds, trees, parks, grass, green roof/walls, tree roots, vegetations, coral reefs, mangroves, sea grasses, oyster reefs, sea salt marshes, sandy beaches and dunes. We conclude that the models and tools that are capable of assessing the multiple benefits, particularly the performance and cost-effectiveness of NBS for HMR reduction and management are not readily available. Thus, our synthesis of modelling methods can facilitate their selection that can maximise opportunities and refute the current political hesitation of NBS deployment compared with grey solutions for HMR management but also for the provision of a wide range of social and economic co-benefits. However, there is still a need for bespoke modelling tools that can holistically assess the various components of NBS from an HMR reduction and management perspective. Such tools can facilitate impact assessment modelling under different NBS scenarios to build a solid evidence base for upscaling and replicating the implementation of NBS.

Abstract. The 1783 Scilla landslide–tsunami (Calabria, southern Italy) is a well-studied event that caused more than 1500 fatalities on the beaches close to the town. This paper complements a previous work that was based on numerical simulations and was focused on the very local effects of the tsunami in Scilla. In this study we extend the computational domain to cover a wider portion of western Calabria and northeastern Sicily, including the western side of the Straits of Messina. This investigation focuses on Capo Peloro area (the easternmost cape of Sicily), where the highest tsunami effects outside Scilla were reported. Important tsunami observations, such as the wave height reaching 6 m at Torre degli Inglesi and flooding that reached over 600 m inland, have been successfully modeled but only by means of a high-resolution (10 m) topo-bathymetric grid, since coarser grids were inadequate for the purpose. Interestingly, the inundation of the small lake of Pantano Piccolo could not be reproduced by using today's coastal morphology, since a coastal dune now acts as a barrier against tsunamis. Historical analysis suggests that this dune was not in place at the time of the tsunami occurred and that a ground depression extending from the lake to the northern coast is a remnant of an ancient channel that was used as a pathway in Roman times. The removal of such an obstacle and the remodeling of the coeval morphology allows the simulations to reproduce the tsunami penetration up to the lake, thus supporting the hypothesis that the 1783 tsunami entered the lake following the Roman channel track. A further result of this study is that the computed regional tsunami propagation pattern provides a useful hint for assessing tsunami hazards in the Straits of Messina area, which is one of the most exposed areas to tsunami threats in Italy and in the Mediterranean Sea overall.

Abstract. The 1783 Scilla tsunami, induced by a coastal landslide occurring during an intense seismic sequence in Calabria (South Italy), was one of the most lethal ever observed in Italy. It caused more than 1500 fatalities, most of which on the 10 beach close to the town where people gathered to escape earthquake shaking. In this paper, complementing a previous work (Zaniboni et al., 2016) focusing on the very local tsunami effects in the town of Scilla, we study the tsunami impact on the Calabria and Sicily coasts out of Scilla. To this purpose we take into account the same landslide geometry considered in the previous study and perform three tsunami simulations, one embracing a larger region with a 50-m computational grid, and two covering the specific area of Capo Peloro, in Sicily, facing Scilla on the western side of the Messina Straits, with even 15 higher resolution (10 m mesh). Numerical results show a very good agreement with the historical observations in Capo Peloro. Moreover, the resulting global tsunami inundation pattern provides a useful hint for tsunami hazard assessment in the Messina Straits area, which is known to be one of the most exposed to tsunami threat in Italy and in the Mediterranean Sea.

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