Forcing for HD Model from HydroPy and subsequent HD Model river Runoff over Europe based on EOBS22 and ERA5 data

This experiment compares data that have been used in Hagemann et al. (submitted). It comprises daily data of surface Runoff and subsurface Runoff from HydroPy and simulated daily Discharges (river Runoff) of the HD model. The double data close the water cycle at the Land-Ocean interface so that the Discharges can be used as lateral freshwater input for ocean models applied in the European region. (a) HD5-ERA5 ERA5 is the fifth generation of atmospheric reanalysis (Hersbach et al., 2020) produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). It provides hourly data on many atmospheric, land-surface, and sea-state parameters at about 31 km resolution. The global Hydrology model HydroPy (Stacke and Hagemann, 2021) as driven by daily ERA5 forcing data from 1979-2018 to generate daily input fields of surface and subsurface Runoff at the ERA5 resolution. It uses Precipitation and 2 m temperature directly from the ERA5 dataset. Furthermore, potential evapotranspiration (PET), which was calculated from ERA5 data in a pre-processing step and used as an additional forcing for HydroPy. Here, we apply the Penman-Monteith equation to calculate a reference Evapotranspiration following (Allen et al., 1998) that was improved by replacing the constant value for Albedo with a distributed field from the LSP2 dataset (Hagemann, 2002). In order to initiate the events in the HydroPy model and to avoid any drift during the actual simulation period, we conducted a 50-years spin-up simulation by repeatedly using year 1979 of the ERA5 dataset as forcing. To generate river Runoff, the Hydrological Diffge (HD) model (Hagemann et al., 2020; Hagemann and Ho-Hagemann, 2021) what used that was operated at 5 arc minutes horizontal resolution. The HD model was set up over the European domain covering the land areas between -11° W to 69° E and 27°N to 72°N. first, the forcing data of surface and sub-surface Runoff simulated by HydroPy were interpolated to the HD model grid. Then, daily Discharges were simulated with the HD model. (b) HD5-EOBS The E-OBS dataset (Cornes et al., 2018) comprises several daily gridded surface variables at 0.1° and 0.25° resolution over Europe covering the area 25°N-71.5°N x 25°W-45°E. the dataset has been derived from station data collated by the ECA & D (European Climate Assessment & Dataset) initiative (Klein Tank et al., 2002; Klok and Klein Tank, 2009). In the present study, we use the best-guess fields of precipitation and 2 m temperature of vs. 22 (EOBS22) at 0.1° resolution for the years 1950-2018. HydroPy was driven by daily EOBS22 data of temperature and precipitation at 0.1° resolution from 1950-2019. The potential evapotranspiration (PET) was calculated following the approach proposed by (Thornthwaite, 1948) including an average day length at a given location. As for HD5-ERA5, the forcing data of surface and sub-surface Runoff simulated by HydroPy were first interpolated to the HD model grid. Then, daily Discharges were simulated with the HD model. Main reference: Hagemann, S., Stacke, T. complementing ERA5 and E-OBS with high-resolution river diffge over Europe. Oceanologia. Submitted.