Propagation of uncertainty across modeling chains to evaluate hydraulic vulnerability in coastal areas

The aim of the thesis is to investigate the propagation of the uncertainties from meteorological to coastal forecasts, in order to obtain a better understanding of the uncertainties associated to the numerical modeling systems. The first phases focused on the parameter settings of the morphological model XBeach, as source of uncertainties within the model itself. This was done by means of a sensitivity analysis of the model that allowed to characterize how the model responds to changes in input, with an emphasis on finding the input parameters to which outputs are the most sensitive. Moreover, an estimate of how the uncertainties propagate within the numerical modeling chain was made by means of the ensemble technique. Moving from a single-deterministic to probabilistic forecasts, it is possible to give some useful indication of the forecast reliability. Therefore, the meteorological Limited Area Ensemble Prediction System COSMO-LEPS was used to generate 16 different meteorological forecasts that were used to force the wave\oceanographic models SWAN and ROMS and finally the morphological model XBeach. The study focused on two different storm events both occurred in the autumn 2015-winter 2016 on the Emilia-Romagna coasts.The results showed that, in both cases, the uncertainties of the wind and pressure fields clearly propagated through to the oceanographic models up to influence the coastal forecasts. The accuracy of the forecasts of the oceanographic and morphological models is largely dependent on the quality in wind data. However, extension of the ensemble approach to the coastal areas showed encouraging results and suggested, as a future development, the possible optimization of the system by using a meteorological ensemble built in such a way as to optimize the spread in terms of the surface variables used to drive the marine-coastal model components

A modeling application of integrated nature based solutions (NBS) for coastal erosion and flooding mitigation in the Emilia-Romagna coastline (Northeast Italy)

Worldwide, climate change adaptation in coastal areas is a growing challenge. The most common solutions such as seawalls and breakwaters are expensive and often lead to unexpected disastrous effects on the neighboring unprotected areas. In recent years, this awareness has guided coastal managers to adopt alternative solutions with lower environmental impact to protect coastal areas, defined as Nature-Based Solutions (NBSs). NBS are quite popular around the world but are often analyzed and implemented individually at pilot sites. This contribution analyzes the effectiveness of two NBS to mitigate coastal impacts (coastal flooding and erosion) under three historical storms along the EmiliaRomagna coasts and the induced improvements due to their potential integration. Through numerical simulations with XBeach, this study demonstrated that the presence of seagrass meadows of Zostera marina produces an average attenuation of 32 % of the storm peak with a maximum attenuation of 89 % in incoming wave height. Seagrass also mitigates flooded areas and maximum inundation depths by 37 % and 58 % respectively. The artificial dune leads to higher mitigation in terms of inundation of the lagoon (up to 75 %), also avoiding any morphological variations behind it. Seagrass has also been shown to be able to reduce beach erosion volumes up to 55 %. The synergic effect of the two NBS improves the capacity to mitigate both inundation (with a benefit of up to 77 % for flooded area attenuation with respect to cases without any defenses) and coastal erosion. Results of the study suggest that the two NBS will work together to produce co-benefits in terms of preservation of their efficiency, development of habitats for organisms and vegetation species, and thereby offering an important social value in terms of possible tourism, recreation and research

On the management of nature-based solutions in open-air laboratories: new insights and future perspectives

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Coastal monitoring for XBeach model calibration in the analysis of the coastal erosion at Cesenatico

Many of the most densely populated areas are located near the coast which is a vulnerable system, affected by erosion and flooding [18].In order to provide an efficient coastal management and coastal risk reduction, a fundamental knowledge of the hydrodinamic and morphodynamic processes in the coastal areas is needed. Numerical models are usually adopted to support long-term and short-term predictions. They need to a proper calibration/validation that is possible thanks to field measurements. XBeach [12] is used in this analysis as a tool to describe the morpho-dynamic coastal behavior. Thanks to a monitoring of a coastal stretch of the Emilia-Romagna littoral, at Cesenatico, it was possible a sensitivity analysis and a morphological calibration of the model

A Digital Twin modelling framework for the assessment of seagrass Nature Based Solutions against storm surges

In this paper we demonstrate a novel framework for assessing nature-based solutions (NBSs) in coastal zones using a new suite of numerical models that provide a virtual "replica" of the natural environment. We design experiments that use a Digital Twin strategy to establish the wave, sea level and current attenuation due to seagrass NBSs. This Digital Twin modelling framework allows us to answer "what if" scenario questions such as: (i) are indigenous seagrass meadows able to reduce the energy of storm surges, and if so how? (ii) what are the best seagrass types and their landscaping for optimal wave and current attenuation? An important result of the study is to show that the landscaping of seagrasses is an important design choice and that seagrass does not directly attenuate the sea level but the current amplitudes. This framework reveals the link between seagrass NBS and the components of the disruptive potential of storm surges (waves and sea level) and opens up new avenues for future studies