1. 66-SE-CMEMS-CALL2: Lot-3
Benefits of dynamically modelled river discharge input for ocean and coupled atmosphere-land-ocean systems
Hao Zuo, Fredrik Wetterhall, Patricia de Rosnay, Ervin Zsoter, Eric de Boisséson

2. 66-SE-CMEMS-CALL2: Lot-3
This study is in line with the R&D priority in CMEMS service evolution to provide continuous enhancement of forcing techniques at lateral boundaries (coasts, open boundaries).
The main objective targets for R&D area 6 for seamless interactions between CMEMS and coastal systems, and two priority topics in CMEMS Call 66: Lot-3
Improved and standardised inputs of freshwater flows (and associated river inputs of particulate and dissolved matter) and homogenised river forcing approaches in global, regional and coastal models;
Improve the interfaces/interactions between coastal monitoring and modelling systems and CMEMS.
This study is also consistent with the R&D area 8 for ocean climate products, indicators and scenarios, by providing improvement in physical consistency and realism in ocean reanalyses, which can be used to infer possible changes in the ocean state at regional and coastal levels.

3. Interests
River freshwater input is crucial in modelling global ocean, i.e. coastal and off-shore SSS, near-surface mixing, freshwater transport, sea-level changes, global climate …
The current CMEMS MFC services rely on river discharge data with various deficiencies
Overly simplistic runoff data: Climatology with no inter-annual variation
Inconsistencies: between atmospheric and hydrologic forcings, and between different services
Development of an improved, consistent and standardised river freshwater input is of interest to all CMEMS services.

4. Objectives The objective of this proposal is
To develop an improved, calibrated and standardised freshwater input to ocean models from river discharge reanalysis driven by atmospheric forcing consistent to the ocean model, capitalizing on recent developments from the Copernicus Services ERA5 and GloFAS.
To assess and report the quantified benefits of using a river discharge reanalysis over climatology as input into global configuration NEMO ocean model.
Such product can provide coastal freshwater boundary conditions for ocean only or coupled atmosphere-land-ocean models, with the potential to enhance the quality of the CMEMS services in the coastal, regional and global scales.

5. Backgrounds CEMS and GloFAS system
The CEMS Global Flood Awareness System (GloFAS, is an operational probabilistic flood forecasting systems (Alfieri et al., 2013). GloFAS couples the runoff from HTESSEL, which is the land surface model of ECMWF Integrated forecasting system (IFS), with a river routing component from the Lisflood hydrological model.
Overview of the GloFAS model setup

6. Backgrounds River-runoff forcing in the NEMO model
Climatological monthly mean river runoff data is commonly used as land boundary freshwater conditions for NEMO ocean model in CMEMS MFC services (e.g. in global high-resolution physical forecasting system and ensemble reanalysis, and daily climatology was used in NWS MFC).
Sensitivity to input river runoff
Ocean states is very sensitive to the land freshwater input, as demonstrated by sensitivity experiments carried out with ECMWF ORAP5 system (Zuo et al 2014), with climatology river runoff forcing from Dai and Trenberth (2002) and variable ratio (20% to 200%).

7. Backgrounds Ensemble spread of SST and SSS
Time series of Atlantic MOC at 26.5N

8. Backgrounds ECMWF Ocean ReAnalysis System 5
Assess of using a GloFAS river discharge reanalysis in the NEMO ocean model will be carried out using the ECMWF ORAS5 system
Ocean: NEMOv3.4
Sea-ice: LIM2
Resolution: ¼ degree with 75 levels
Assimilation: 3DVAR-FGAT
River runoff
Overview of the ORAS5 setup

9. Work plan WP1: System development
WP 1.1 Production of historical river discharge data with GloFAS system
Forced with ERA5 atmospheric reanalysis (C3S product)
Daily discharge
0.1 degree resolution
Covers
Output in netCDF format

10. Work plan WP1: System development
WP1.2 Implementation of GloFAS river discharge into the NEMO ocean model
GloFAS river discharge reanalysis will be processed to create river runoff forcing suitable for the NEMO ocean model as described in Bourdallé-Badie and Treguier (2006).
identify major rivers and sort them by order of annual discharge magnitude
apply coordinate mapping from river coastal discharge to ocean model
apply river mouth shifting if necessary
apply coastal repartition (spread)

11. Work plan WP2: System evaluation
WP2.1 Design/run impact study experiments using different runoff forcings
Using ORAS5 equivalent system for impact study
Driven by the same ERA5 forcing as input river runoff data
Identify optimized runoff parameter settings for NEMO model
Run twin experiments (Climatology VS GloFAS reanalysis)
P1:
P2:

12. Work plan WP2: System evaluation
WP2.2 Assessment of the impact of GloFAS runoff forcing using ORA
Assessment on both global and regional scales, against independent observation data sets (CMEM TAC product, if exist), for the following ECVs
Sea levels
Sea surface salinity
Sea surface temperature
Ocean heat content
Meridional Overturning Circulation
Sea-ice conditions

13. Example ECV: Sea ice Sea ice concentration (201509) Control run
Ensemble spread with different river runoff input

14. Outcomes
A global river discharge reanalysis data set from the GloFAS system from 1979 to 2016, driven by ERA5 forcing
A NEMO compatible river runoff data set derived from GloFAS reanalysis
Conducting impact study experiments within the ECMWF Ocean ReAnalysis (ORA) system
Assessment of the new GloFAS-based runoff forcing in global ocean and coastal areas, on ocean Essential Climate Variables' (ECVs) simulations.

15. Expected Benefits
A improved river discharge data set for CMEMS services
CEMS GloFAS river-discharge reanalysis driven by ERA5 forcing
Unprecedented temporal and spatial resolution with realistic variability
Consistent atmospheric boundary conditions in both the hydrology and ocean components
Homogenised river forcing approaches in global, regional and coastal model
Lesson learned from product assessment will be passed on to CMEMS
Improve interaction between coastal monitoring and modelling system and CMEMS by removing the inconsistency in land freshwater inputs seen by different systems
Building synergies between C3S, CEMS and CMEMS

16. Deliverables Quarterly report (every 3 months) Mid-term report (K+12)
Final report (K+23)
GloFAS global river discharge reanalysis data set (K+23)
The proposed GloFAS river discharge reanalysis data set will be made easily available to the user community, and could be disseminated through the C3S Climate Data Store. The NEMO compatible GloFAS-based run-off data can be made available but only for NEMO configuration used by ECMWF.

17. Project team Hao Zuo (PI), ECMWF Fredrik Wetterhall, ECMWF
Patricia de Rosnay, ECMWF
Ervin Zsoter, ECMWF
Eric de Boisséson, ECMWF

18. Thank you for your attention
Any question?