Impact of a fully coupled high-resolution medium range hydrometeorological forecast in an ensemble framework: evaluation of a case study in the Calabria peninsula (Southern Italy)

Abstract:

Orographically complex regions, such as the Mediterranean coastal areas, are often prone to extreme hydrometeorological events. High-resolution mesoscale models operating at convection-permitting scales are needed to accurately describe the weather dynamics and the related impact on the ground since they allow improving the representation of interactions between the subsurface, surface, and low atmosphere. Such models can further benefit from the adoption of fully-coupled atmospheric-hydrological approaches, which are becoming increasingly popular. However, the uncertainties associated with the high-resolution weather forecasting remain high, therefore probabilistic approaches based on multiple forecasts are advisable.

While previous studies showed that fully-coupling effect on deterministic short-range forecasts is minor compared to other sources of uncertainty, this note aims to evaluate the potential benefit given by stronger atmospheric-hydrological interaction in medium-range hydrometeorological ensemble forecasts. Specifically, an ensemble of 50 members, in which boundary conditions are provided by the Ensemble Prediction System (EPS) operational at the European Centre for Medium-Range Weather Forecasts (ECMWF), is dynamically downscaled through the high-resolution mesoscale Weather Research and Forecasting (WRF) model, to provide a seven-days-in-advance forecast of a severe event affecting the Calabria region (Southern Italy) on November 2019. This work illustrates how the fully coupled approach influences the forecast of an extreme meteo-hydrological event in an ensemble framework, not only in terms of rainfall prediction but also investigating the effects on soil moisture conditions immediately before the flood events. The hydrological analysis will regard the discharge distribution in the whole Calabrian river network, highlighting the potential benefit of the modelling system in a medium-range ensemble operational hydrometeorological framework.