The Irish Atlantic CoCliME case study configuration, validation and application of a downscaled ROMS ocean climate model off SW Ireland

This ocean numerical modelling study is focused on the shelf waters off southwest Ireland. Outputs from the model are used to provide scientists and policy makers with climate change information related to oceanic conditions that influence harmful algal blooms in the region. Four simulations were developed to include a 20-year hindcast simulation (1997-2016), a 31-year historical simulation (1975-2005), and two 30-year future climate model projections (2006-2035) for the representative carbon pathways (RCP) 4.5 and 8.5 scenarios. We evaluated the hindcast model skill by comparing the simulation outputs with measured observational data and calculated statistics such as the bias, and the root mean square error (RMSE). The observations consisted of satellite sea surface temperature and, CTD temperature and salinity profile data collected in Irish waters. The sea surface temperature RMSEs between the 20-year hindcast simulation and the satellite data were ca. 0.50°C. A minimum RMSE of ca. 0.20°C was recorded in December 2015. The basin-averaged bias (difference) and RMSE for near bottom temperature between the RCP 4.5 and the historical simulation was 0.14°C and 0.27°C respectively. The sea surface temperature anomaly pattern for the RCP 8.5 shows warming across the whole model domain. The sea surface salinity and near bottom salinity climate simulation anomaly maps indicate a general freshening on the southwest Irish shelf. A change of ca. 0.2 sea surface salinity and near bottom salinity was observed. The RCP 8.5 simulation shows the highest current velocities when compared to other simulations. The Irish coastal current pattern under the RCP 8.5 scenario appears very intense and well defined with a velocity > 20 [cm/s].