Advances in the understanding and modelling of surface currents have revealed the importance of internal waves, mesoscale and submesoscale turbulence. Indeed all these features should have a large influence on wind waves, and in particular wave heights are expected to be modified by refraction. Still, the quantitative impact of currents on waves is not well known due to the complexity of the random wave fields and currents that are found in the ocean, and the lack of observations of both currents and waves at scales shorter than 150 km. Here we use novel satellite altimetry data and state of the art phase-averaged numerical wave models forced by currents at different resolutions in the Agulhas region. We find that a numerical wave model that uses surface currents with resolutions of 30 km or less and a directional resolution of 7.5 ◦ or less, can provide accurate representations of the significant wave height gradients found in the Agulhas current. Using smoother current fields, such as derived from satellite altimetry alone, generally underestimates gradients and extreme wave heights. This work suggests that high resolution satellite altimetry data can be combined with numerical wave models to provide a statistical validation of surface current gradients.