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Historical wave trends are studied via ECMWF's reanalyses over the 20th century. • ERA20 is calibrated via quantile-matching and validated against buoy measurements. • The wave energy resource increases over 40% off the west coast of Ireland. • A 30% surplus of AMPP is observed for different WECs due to resource variations. • Extreme events occurrence doubled, doubling the time WECs spend in survival mode.

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In this article, offshore wind energy potential is measured around the West Mediterranean using the WRF meteorological model without 3DVAR data assimilation (the N simulation) and with 3DVAR data assimilation (the D simulation). Both simulations have been checked against the observations of six buoys and a spatially distributed analysis of wind based on satellite data (second version of Cross-Calibrated Multi-Platform, CCMPv2), and compared with ERA-Interim (ERAI). Three statistical indicators have been used: Pearson's correlation, root mean square error and the ratio of standard deviations. The simulation with data assimilation provides the best fit, and it is as good as ERAI, in many cases at a 95% confidence level. Although ERAI is the best model, in the spatially distributed evaluation versus CCMPv2 the D simulation has more consistent indicators than ERAI near the buoys. Additionally, our simulation's spatial resolution is five times higher than ERAI. Finally, regarding the estimation of wind energy potential, we have represented the annual and seasonal capacity factor maps over the study area, and our results have identified two areas of high potential to the north of Menorca and at Cabo Begur, where the wind energy potential has been estimated for three turbines at different heights according to the simulation with data assimilation.

This paper presents a pioneering attempt to evaluate the impact of long-term seasonal wave energy trends on hydrodynamic capture by wave energy converters (WECs) over the 20th century. The ERA20c reanalysis generated by the European Centre for Medium-Range Weather Forecasts is calibrated against the ERA-Interim reanalysis via the quantile matching technique, and validated against buoy measurements across the Northeast Atlantic Ocean. The study focus is the seasonal variation of wave resources over the 20th century, so the calibration is performed using seasonally classified reanalysis and measured data. Results show that wave energy flux increased to 3 and 2 kW/m per decade in winter and spring/autumn, respectively, and that the frequency of off-limit events, defined as sea-states with significant wave height of over 5 m, has doubled over the 20th century. The impact of such wave energy trends is analysed in this paper using an oscillating wave surge converter, which shows steadily increasing power absorption over the 20th century. However, as a result of higher decadal trends and the increase in off-limit events, the hydrodynamic efficiency of the WEC, referred to as the capture width ratio, decreases up to 20%.1. The wave energy flux and its inter-annual variability (analysing the seasonal cycle), 2. The bi-dimensional probability density function, or scatter diagram, given by the wave period and the wave height, and 3. The probability of occurrence of off-limit events, where the WEC needs to activate its survival mode.In general, wave data from previous one, two or three decades are used for assessing the resource and power production capabilities of WECs in a given location [9][10][11][12][13][14][15]. However, by only considering data