A projection of the expected wave power in the Black Sea until the end of the 21st century
Introduction
In the last years, the increased concerns regarding the necessity to reduce greenhouse gas (GHG) emissions have led to direct more attention to renewable energies as a real option for carbon reduction. The International Renewable Energy Agency (IRENA) and International Energy Agency (IEA) established that by 2050, based on accelerated deployment of renewables together with increased energy efficiency, 90% of the required carbon reductions can potentially be achieved [1]. It is widely accepted that ambitious efforts and effective measures need to be undertaken by the nations to reduce global warming. The Paris Climate Agreement [2] formulated in 2015 by the United Nations Framework Convention on Climate Change (UNFCCC) established as the main target to maintain the rise of the global temperature this century well below 2° Celsius above pre-industrial levels.
In the marine environment, various renewable energy resources are available (e.g. from wind, wave, and currents) with the potential to ensure an important part of the energy demands, and also with a positive impact on the global warming brought by the reduction of fossil fuels [3]. Moreover, such resources can be a solution for isolated areas to have energy independence and sustainable development, as is the case of islands in general [4], or the particular case of S. Vicente Island from the Cape Verde archipelago [5]. The wave energy has a relevant potential among marine renewable resources due to its characteristics as high concentration and less variability. Although the deployment of the wave farms advances slowly, promising expectations are ahead thanks to the important investments in the development of the wave energy conversion technologies [6]. In recent years, various studies for the wave energy assessment were developed for finding the best places around the world to catch this energy. Assessments of the wave energy resources available in various continents were made. Thus, in America the wave energy resource of Peru was estimated using buoy measurements and SWAN (acronym from Simulating Waves Nearshore [7]) model results, showing that the offshore wave energy potential is from moderate to high, with the advantage of the low seasonal variability of the resources [8]. A recent study assessed the wave energy resource for the coastal waters of the United States based on numerical modelling results to evaluate regional opportunities and constraints for wave energy converter projects [9]. The southern coast of Brazil was also the target of a study [10] to evaluate the wave energy potential in deep and shallow waters, showing that this area has potential for wave energy exploitation. In Asia the SWAN model was used to provide the sea state characteristics over 20-year period in the China adjacent seas, with the objective to find the most promising areas for harvesting wave energy [11]. The wave energy in the northern Persian Gulf using the SWAN model results and a new method to specify the optimal location for wave energy harvesting was also investigated [12]. Based on data covering extended time intervals, both short-term variation and long-term change were evaluated for sustainable wave energy farm projects in Australia [13]. Abundant wave energy resources are found especially in the southern coast of Australia [14]. In Europe various studies pointed out the available wave energy resources, especially on the western Iberian coast. Thus, along the Galician coast (NW Spain) the SWAN model was implemented and using a specific tool the wave energy potential was evaluated based on the wave model results [15], while on the Portuguese coast the influence of tides on the wave energy was accounted [16].
The importance of wave climate forecasting for nearshore wave energy exploitation is pointed out by a study performed on the southern coast of Spain [17]. The most energetic area for wave energy exploitation in the Mediterranean Sea is the western side of the basin (between the Balearic Islands, Sardinia and Corsica and the northern coast of Algeria) with a yearly mean wave power of about 10 kW/m along the coast [18]. The wave energy resources in the Black Sea basin were also assessed based on the SWAN results over 30-year period, showing that the western side of the basin presents the highest resources [19], and using nested high resolution domains the most promising nearshore areas can be found [20]. The temporal variation of the wave energy flux in some locations of the Black Sea southern coast (Turkish coast) was also investigated [21]. The European offshore wind and wave energy resource were assessed to study the possibility to combine their exploitation [22]. Special targets to develop wave energy farms are the islands, which are isolated environments such as Cape Verde Islands [23] or the Island of Fuerteventura in the Canarian archipelago (Spain) [24].
The wave energy conversion efficiency in various nearshore areas was discussed in various studies e.g. [25]. A very important issue is the optimization of the wave energy converters arrays, with the focus to maximize the performance and efficiency of the array [26]. Another important issue regarding the exploitation of wave power is related to its variability [27]. Moreover, the variability of the wave power can be reduced using co-located wind-wave farms [28]. The implementation of the hybrid energy farms represents another solution to counteract the resource variability [29].
In this general context which brought attention to the exploitation of renewable resources, the present work is a follow-up of a previous study regarding the future wave energy expected in the Black Sea [30]. The focus is now on the evaluation of the present wave climate corresponding to the historical period (1976–2005) against altimeter measurements to check the reliability of results and on the evaluation of the wave energy pattern in the last 30-year time interval (2071–2100) of the 21st century under two Representative Concentration Pathways (RCPs) emission scenarios (RCP4.5 and RCP8.5 [31]). RCP4.5, which might be considered as the most plausible scenario [32], assumes that the peak of the carbon dioxide (CO2) emissions is expected around the year 2040 and that this peak will be followed by a decline. On the other hand, the most pessimistic scenario is RCP8.5, which assumes an increase in emissions along the entire 21st century and afterwards. The same wave modelling system based on the SWAN model, previously implemented, calibrated and validated to simulate the wave conditions in the Black Sea [33], has been also used to assess the wave power for the period 2071–2100. The reliability of the sea state conditions simulated by SWAN model in the Black Sea is strengthened by another study [34]. The importance of the wind field resolution used to force the SWAN model in this basin was also evaluated [35]. On the other hand, the SWAN model was used extensively to assess the wave energy potential in various locations around the world, as mentioned above. The wind fields simulated by a Regional Climate Model (RCM), namely the Rossby Centre regional atmospheric model, under RCP4.5 and RCP8.5 emission scenarios are used to drive the wave model.
The impact of climate change on the wave power in the Black Sea along the 21st century is estimated by performing comparisons with previous results obtained for 30-year time-slices covering the near future (2021–2050) and historical (1976–2005) periods. In this way, a more comprehensive picture of the expected wave power dynamics in the basin of the Black Sea is provided.
Section snippets
Methodology
For a detailed wave resource assessment in the Black Sea the SWAN model is used to perform simulations in the last 30-year time interval of the 21st century. A validation of the present wave climate against altimeter measurements is also accomplished. Details about the SWAN model implementation and validation in the Black Sea basin are given below.
Results
In this section an evaluation of the distant future wave power potential is carried out considering both RCP4.5 and RCP8.5 emission scenarios. This includes analyses of the monthly, seasonal and annual mean wave power. Furthermore, a study of the expected wave dynamics in the Black Sea is also performed by comparing the results from the future with the present wave power.
Conclusions
In the present study, wave model simulations have been performed in the Black Sea basin forcing the wave model with wind fields from an RCM model (RCA4), which is provided by EURO-CORDEX. A validation of the simulated significant wave heights against altimeter measurements has been first performed in order to have a quality assessment of the results delivered by the modelling system based on the SWAN model driven with RCM wind fields. The values of the statistical parameters are in line with
Acknowledgements
This work was carried out in the framework of the project ACCWA (Assessment of the Climate Change effects on the WAve conditions in the Black Sea), supported by Romanian Ministry of Research and Innovation, CNCS-UEFISCDI (the Romanian Funding Agency forScientific Research), project number PN-III-P4-ID-PCE- 2016-0028, within PNCDI III (the Romanian National Program for Research,Development and Innovation) and in the framework of the ESA Climate Change Initiative for Sea State project. The wind
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