Wave trends have been shown to be relevant to energy generation in various areas of the world. Accordingly, this article describes the impact of wave trends on the design of oscillating water column wave energy converters. First, wave trends across the North-East Atlantic Ocean are analysed based on the ERA5 reanalysis. In addition, an empirical model that provides the capture width of an oscillating water column is employed, identifying an approximately linear relationship between the average wavelength and the optimal width of the chamber. Thus, combining wave trends and the empirical model, the optimal size of the chamber is found to vary significantly between different geographical locations and over the four decades between 1979 and 2018. Differences between the original geometry and the geometry optimised considering wave trends, reach up to 15% in some locations. As a consequence, oscillating water column chambers designed based on past available resources rather than the resource corresponding to the time when the device is to be deployed are demonstrated to be inefficient, with a significant difference in the optimal width and absorbed energy of the chamber. Accounting for changes in resource availability over time may assist in cost optimisation of unconventional renewable energy technologies.