Do land parameters matter in large-scale terrestrial water dynamics? – Toward new paradigms in modelling strategies

Abstract. Large-scale variations of terrestrial water storages and fluxes are key aspects in the Earth system, as they control ecosystem processes, feed back on weather and climate, and form the basis for water resources management. However, relevant observations are limited and process models used for estimation are highly uncertain. These models rely on approximations of terrestrial processes as well as on location-specific parameters (e.g.;soil types, topography) to translate atmospheric forcing (e.g.;precipitation, net radiation) into terrestrial water variables (e.g.;soil moisture, river flow). To date it is unclear which processes and parameters should be included to model terrestrial water systems on regional to global scales. Using a data driven approach we show, that skillful estimates of monthly water dynamics in Europe can be derived from information on atmospheric drivers alone and that the inclusion of land parameters does not improve the estimate. The results highlight that substantial parts of terrestrial water dynamics are controlled by atmospheric forcing, which dominates over land parameters. This is not reflected in current model developments, which are striving at incorporating an increasing number of small scale processes and related parameters. Our results thus point at major potential for theory and model development, with important implications for water resources modelling, seasonal forecasting and climate change projections.