## 1 Introduction  
### Motivations and Perspective  
If it is true that the first two decades of the 21 st century will be remembered as those of maximum scientific and political discussion on the warming of the climate system, then the following two decades will probably focus on the options for countering the impact and future risks of climate trends. While the scientific aspect of the climate change was in the hands of a few categories, now ahead lies a general page, for whoever is on call, in order to face the challenges in the near future. For instance, the marine and maritime engineering community is pushing hard to provide solutions in the blue energy sector [1], which could give a significant contribution to the greenhouse gas reduction objectives. The exploitation of energy from the sea though Wave Energy Converters (WECs) is increasingly catching on, and numerous technological solutions are renovating this field [2; 3]. The idea to integrate WECs into traditional coastal structures is not recent, and lately, it is moving toward the highest level of research and development [4; 5; 6; 7; 8; 9; 10]. Nowadays, ninety-seven percent of climate scientists (they were 95% in 2013 [11]) agree that climate-warming trends over the past century are extremely likely due to the heat-trapping nature of carbon dioxide and other gases related to human activities [12]. Unfortunately, the first symptoms of climate change have begun to appear, so it is now necessary to take action, not only on the causes of the global warming, but also on its effects. Changes in the polar ice caps, ocean temperatures, atmospheric sea level pressure, wind fields, precipitation patterns, ocean currents and water mass distribution seem to be confirmed by several studies, leading worldwide scientific organizations to issue public statements endorsing this position. The sea level rise (SLR) and the intensification of extreme wave climate events represent one of the major issues of global concern [13]. SLR affects the extreme statistics of both nearshore significant wave height and water level, resulting in an increase of overtopping in terms of discharge volumes and frequency of overtopping events [14; 15; 16]. This issue needs to be carefully addressed during planning, design and maintenance of coastal defenses and related risk-management strategies [17]. Present day risks may substantially be altered and generate a need to revisit existing costal defenses by developing alternative and innovative countermeasures. For their part, some coastal engineers and researchers involved in the renewable energy sector are focusing their effort on the combination of WECs into harbor breakwaters [18; 19; 20], which could represent a smart alternative with other adding values, e.g., just the protection against SLR. The present work analyzes a specific measure to counteract the increased overtopping due to SLR to be embedded into a WEC-breakwater technology called Overtopping BReakwater for wave Energy Conversion (OBREC) [21; 22; 23]. This device is able to extract energy through the wave-overtopping phenomenon. Instead of dissipating the incoming wave energy, OBREC uses a single reservoir, placed on a traditional rubble mound breakwater or on a vertical caisson breakwater, to harvest this energy and transform it into electricity (Figure 1). After the system collects the overtopping water above the sea level, thanks to a sloping ramp, the flow is driven toward low head turbines in the reservoir, to generate electrical energy [24; 25]. Figure 1: Conceptual design and key components of the Overtopping BReakwater for wave Energy Conversion (OBREC) (wave flow direction from left to right). A full-scale prototype of OBREC is currently working at Naples Harbor, in Italy. It represents the first non-conventional breakwater in the world which exploits the overtopping phenomenon to produce clean energy.