1 Dataset description This experiment comprises data that have been used in Hagemann et al. (in preparation). It comprises monthly evapotranspiration time series as well as daily data of surface runoff and subsurface runoff from the global hydrology model HydroPy and simulated daily discharges (river runoff) of the HD model, which are based on EOBS31 data (see below). On the one hand, the discharge 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. On the other hand, they can be used to investigate climate induced trends in discharge without considering direct human impact on the river runoff, e.g. by regulation or water abstractions. Please note that a predecessor version of this dataset based on EOBS22 data was published as Hagemann and Stacke (2021) and discussed by Hagemann and Stacke (2023).

                1.1 EOBS data
                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). To simulate river runoff of the current dataset version 1, we use the best-guess fields of precipitation and 2m temperature of E-OBS vs. 31 (EOBS31) at 0.1° resolution for the years 1950-2024.

                1.2 The HD model
                The HD model (Hagemann et al., 2020) is a river-routing model that is well-established and implemented in a range of global and regional model systems. The HD model can be forced by daily or sub-daily time series of surface and subsurface runoff from the driving climate, land surface or hydrology model. In the present study, we applied the HD model v5.2.4 (Hagemann et al., 2025) over its European domain (land areas between 11°W to 69°E and 27°N to 72°N) at 1/12° spatial resolution.

                1.3 European EOBS-based high-resolution river runoff
                Analogous to Hagemann and Stacke (2022), the global hydrology model HydroPy (Stacke and Hagemann, 2021) and the HD model were used to simulate daily discharge time series over the European domain at 1/12° horizontal resolution. HydroPy was driven by daily EOBS31 data of temperature and precipitation at 0.1° resolution from 1950-2024. The potential evapotranspiration (PET) was calculated following the approach proposed by Thornthwaite (1948) including an average day length at a given location. We conducted a 50-years spin-up simulation by repeatedly using forcing of the year 1950 before the actual simulation was started. Noticeable differences to the EOBS22-based simulation considered by Hagemann and Stacke (2022) occur over Spain and Turkey. Over Turkey, this can be considered as an improvement as the data gaps of EOBS v. 22 over Turkey, which were identified by Hagemann and Stacke (2022), are not present in EOBS31. The daily time series of surface and sub-surface runoff generated by HydroPy were interpolated to the European HD model domain and then used to simulate daily discharges with the HD model. The resulting daily time series of river runoff (HD5-EOBS31) covers the full EOBS31 period 1950-2024.

                Acknowledgments
                This dataset was generated while receiving basic funding in the POF IV program “Changing Earth – Sustaining our Future” of the Helmholtz Association (HGF), Germany.