Projecting future changes in wave climate and coastal response in Portugal by the end of the 21st century

This work presents an assessment of projected changes in the wave climate affecting the western coast of mainland Portugal by the end of the 21(st) century by means of comparing a 30-year reference wave regime with an equivalent IPCC-based future scenario in 2060-2099. The HadCM3 model yielded both the reference and future wind fields necessary to force ocean waves, which have been simulated using the MAR 30 model, previously validated using Waverider data. Results suggest that mean wave height may remain essentially invariant though its intra-annual distribution will change. In addition, the projection includes a rotational shift in wave direction and this may have relevant impacts in the equilibrium condition of the coastal sediment budget. These impacts have been simulated in terms of modulation of the longshore solid transport in the sand-starved, drift-aligned coast of Espinho-Cabo Mondego (NW Portugal). Results suggest that refraction effects will attenuate the directional shift imposed in deep water and that this attenuation comes out as non linear. At the present level of knowledge, an increase of about 5-15% in net littoral drift is within limits of plausibility in the future scenario; in addition, numerical results indicate that increase in intensity of the future longshore transport will not exceed 25%, regardless the magnitude of the rotational shift imposed in deep water wave regime. We anticipate increased erosion in the studied coast in response to prospected directional changes in wave climate but this increase may well remain within manageable limits.