The Hydrological Discharge (HD) model The Hydrological Discharge (HD) model calculates the lateral transport of water over the land surface to simulate discharge into the oceans. It has been validated and applied in many studies since the publication of its original global 0.5° version (Hagemann and Dümenil, 1998; Hagemann and Dümenil Gates, 2001). Recently, a new version 5.0 has been developed that can be applied globally at a 5 Min. (~8-9 km) resolution. This HD version was applied and validated over Europe by (Hagemann et al., 2020; Hagemann & Stacke, 2022). The HD model has been coupled to several global and regional ESMs (cf. Hagemann et al., 2020). It separates the lateral water flow into the three flow processes of overland flow, baseflow, and riverflow. Overland flow and baseflow represent the fast and slow lateral flow processes within a grid box, while riverflow represents the lateral flow between grid boxes. The HD model requires gridded fields of surface and subsurface runoff as input for overland flow and baseflow, respectively, with a temporal resolution of one day or higher. The present version 5.2 comprises several changes that are described in the files history.md that should be previewed below as well as in the file ./scr/docu/history.md. Installation You have have to uncompress the tarfile hdmodel_5_2.tgz in your desired code directory and then follow the instructions in ./scr/docu/readme_hd_model.md to modify and run the compile and run scripts in a linux/unix environment. In order to run the HD model, you need to download the HD model parameter files Vs. 5.1 that are published as dataset on Zenodo.This dataset comprises parameter fields at 0.5° global resolution and at 5 Min. resolution (global, Europe). The script hdpara_cut.ksh cuts out a regional subdomain from the global 5 Min. HD parameter file (see ./docu/readme_hd_model.md - Sect. 3.). Gridboxes that may laterally flow out of the domain at the regional boundaries are converted into sinks to avoid numerical exceedances of array bounds. An examples is provided for Europe. Further regional domains should be implemented analogously. Remark for coupling purposes Note that this HD model distribution should include everything that is necessary to run the standalone/offline version of the HD model. The HD model is also equipped with coupling capabilities using the couplers YAC or OASIS. Information on coupling issues is provided in the file ./docu/readme_coupling.md Copyright and Licenses Copyright 2021: Institute of Coastal Systems - Analysis and Modelling, Helmholtz-Zentrum Hereon HD model code is licensed under the Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0) Authors: HD Model up to Vs 5.1: Stefan Hagemann, Ha Ho-Hagemann Authors: HD Model Vs. 5.2+: Stefan Hagemann, Ha Ho-Hagemann, Moritz Hanke Main Contact: Stefan Hagemann, Helmholtz-Zentrum Hereon, Email: stefan.hagemann@hereon.de Acknowledgements We acknowledge contributions of colleagues (see code headers) from the Max Planck Institute of Meteorology (MPI-M) and collaborating institutions who developed various infrastructure routines and who contributed to the implementation of the HD model into the coupled system ECHAM5/MPIOM and its successor MPI-ESM. We especially appreciated the help of Otto Böhringer (MPI-M) who separated the HD code from the fixed association with the MPI-ESM infrastructure. We are also grateful to Veronika Gayler (MPI-M) for her adapatations to Fortran90 and the implementation of various diagnostics. References Main publication for 5 Min. version of HD model (Vs. 4+): Hagemann, S., T. Stacke and H. Ho-Hagemann (2020) High resolution discharge simulations over Europe and the Baltic Sea catchment. Front. Earth Sci., 8:12. doi: 10.3389/feart.2020.00012. First publication using HD Vs. 5: Hagemann, S., Stacke, T. (2022) Complementing ERA5 and E-OBS with high-resolution river discharge over Europe. Oceanologia, doi:10.1016/j.oceano.2022.07.003. Further basic HD publications (Vs. 1, 0.5 degree) Hagemann, S., L. Dümenil (1998) A parameterization of the lateral waterflow for the global scale. Clim. Dyn. 14 (1), 17-31 Hagemann, S., L. Dümenil Gates (2001) Validation of the hydrological cycle of ECMWF and NCEP reanalyses using the MPI hydrological discharge model, J. Geophys. Res. 106, 1503-1510 First publication using coupled 5 Min. version of HD model over Europe Ho-Hagemann, H.T.M., Hagemann, S., Grayek, S., Petrik, R., Rockel, B., Staneva, J., Feser, F., and Schrum, C. (2020) Internal variability in the regional coupled system model GCOAST-AHOI, Atmos., 11, 227, doi: 10.3390/atmos11030227

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Minor bug fix necessary for OASIS coupling: 1. Overlooked inconsistency that some compilers do not notice. However, the SX-nfort does. In ./code/src/oas_hd.f90 - line 573 (routine decomp_def): remove the DIMENSION(id_size) so that the line becomes: INTEGER, INTENT(out) :: id_paral(OASIS_Box_Params) 2. On a NEC system. you may need to remove CALL util_backtrace in routine *mo_exception.f90 - line 110*, as this may cause a compilation error. 3. In the coupling of HD using YAC and icpl_mask_tohd = 2, the array hd_receive_mask is currently read as integer from the file hd_receive.nc, which will cause problems if the mask is fractional. Solution before the next release is to generate this mask already as a 0/1 mask without fractions.