River Freshwater Contribution in Operational Ocean Models along the European Atlantic Façade: Impact of a New River Discharge Forcing Data on the CMEMS IBI Regional Model Solution

35 pages, 12 figures, 7 tables.-- Data Availability Statement: The following publicly available datasets were analyzed in this study: Model data: The CMEMS IBI MFC operational forecast product can be found in the CMEMS catalogue (IBI-MFC forecast analysis product: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=IBI_ANALYSISFORECAST_PHY_005_001 (accessed on 8 April 2021)); LAMBDA river data can be found in: http://www.cmems-lambda.eu/#data-portal (accessed on 8 April 2021); data from the different ocean model scenarios analyzed in the study can be available on request from the corresponding author. Observational data: The data from in-situ buoys, Argo floats and Recopesca can be found in the CMEMS catalogue (Insitu-TAC Near-Real-Time observational product: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=INSITU_IBI_NRT_OBSERVATIONS_013_033 (accessed on 8 April 2021)). The salinity data from SMOS (the low-resolution level 3 SSS product computed with smoothening spatial window of 50-km radius) can be found in the BEC public ftp catalogue: http://bec.icm.csic.es/bec-ftp-service/ (accessed on 8 April 2021); Finally, the INTECMAR and IPMA observational salinity datasets used in this study are 3rd Party Data, and restrictions are applied to their availability (contact with the institutions owner of these datasets would be required for access permission)River freshwater contribution in the European Atlantic margin and its influence on the sea salinity field are analyzed. The impacts of using a new river discharge database as part of the freshwater forcing in a regional ocean model are assessed. Ocean model scenarios, based on the CMEMS (Copernicus Marine Environment Monitoring Service) operational IBI-MFC (Iberia Biscay Ireland Monitoring Forecasting Centre) model set-up, are run to test different (observed, modeled and climatological) river and coastal freshwater forcing configurations throughout 2018. The modelled salinity fields are validated, using as a reference all known available in-situ observational data sources. The IBI model application is proven to adequately simulate the regional salinity, and the scenarios showcase the effects of varying imposed river outflows. Some model improvement is achieved using the new forcing (i.e., better capture of salinity variability and more realistic simulation of baroclinic frontal structures linked to coastal and river freshwater buoyancy plumes). Major impacts are identified in areas with bigger river discharges (i.e., the French shelf or the northwestern Iberian coast). Instead, the Portuguese shelf or the Gulf of Cadiz are less impacted by changes in the imposed river inflows, and other dynamical factors in these areas play a major role in the configuration of the regional salinityPart of this research work was conducted in the framework of the following 2 projects: The EU Interreg Atlantic Area MyCoast Project EAPA_285/2016 (F.C., A.M. and M.G.S.) and the CMEMS Service Evolution Project LAMBDA (F.C., F.S., E.O. and A.N.). It was also supported by activity from the CMEMS IBI-MFC (K.G., P.L. and A.A.B.)With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)Peer reviewe