1 Fully coupled high-resolution medium-range forecasts: evaluation 2 of the hydrometeorological impact in an ensemble framework 3 4 L. Furnari1, L. Magnusson2, G. Mendicino1 and A. Senatore1 5 6 1 Department of Environmental Engineering, University of Calabria, Rende (CS), Italy 7 2 European Centre for Medium‐ Range Weather Forecasts, Reading, UK 8 9 Corresponding author: Luca Furnari (
[email protected]) 10 11 12 13 Manuscript first submitted to Hydrological Processes in Febraury 2021 14 15 16 Keywords 17 Fully coupling, atmospheric-hydrological modeling chain, medium-range forecast, terrestrial 18 water lateral transport, ensemble forecast, WRF-Hydro, ECMWF ENS, Mediterranean 19 1 1 2 20 Abstract 21 Fully coupled atmospheric-hydrological models allow a more realistic representation of the 22 land surface–boundary layer continuum, representing both high-resolution 23 land-surface/subsurface water lateral redistribution and the related feedback towards the 24 atmosphere. This study evaluates the potential contribution of the fully coupled approach in 25 extended-range mesoscale hydrometeorological ensemble forecasts. Previous studies have 26 shown, for deterministic simulations, that the effect of fully coupling for short-range forecasts 27 is minor compared to other sources of uncertainty, however, it becomes not negligible when 28 increasing the forecast period. Through a proof-of-concept consisting of an ensemble (50 29 members from the ECMWF Ensemble Prediction System) seven-days-in-advance forecast of 30 a high impact event affecting the Calabrian peninsula (southern Italy, Mediterranean basin) on 31 November 2019, the paper elucidates the extent to which the improved representation of the 32 terrestrial water lateral transport in the Weather Research and Forecasting (WRF) – Hydro 33 modeling system affects the ensemble water balance, focusing on the precipitation and the 34 hydrological response, in terms of both soil moisture dynamics and streamflow in 14 35 catchments spanning over 42% of the region.