Using river flow data from the FRIEND European Water Archive (Gustard, A. [ed.] : Flow Regimes from International Experimental and Network Data [FRIEND]. In Hydrological Studies, Vol. 1. Institute of Hydrology, Wallingford, UK) and climatological data from the Climate Research Unit, University of East Anglia (Hulme, M., Conway, D., Jones, P.D., Barrow, E.M., Jiang, T. and Turney, C. : A 1961-90 climatology for Europe for climate change modelling and impacts applications. In Int. Jnl. Clim., Vol. 15, p. 1333-1363).
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Based on gauged data from hydrometric networks. Run-off in ungauged areas estimated from an empirical relationship relating run-off to precipitation and potential evaporation (Budyko, M.I. and Zubenok, L.I. : The determination of evaporation from the land surface. Izv. Akad, Nauk SSSR. In Ser. Geogr., No 6, p. 3-17).