Abstract. Operational meteo-hydrological forecasting chains are
affected by many sources of uncertainty. In coastal areas characterized by
complex topography, with several medium-to-small size catchments,
quantitative precipitation forecast becomes even more challenging due to the
interaction of intense air–sea exchanges with coastal orography. For such
areas, which are quite common in the Mediterranean Basin, improved representation of
sea surface temperature (SST) space–time patterns can be particularly
important. The paper focuses on the relative impact of different resolutions
of SST representation on regional operational forecasting chains (up to
river discharge estimates) over coastal Mediterranean catchments, with
respect to two other fundamental options while setting up the system, i.e.
the choice of the forcing general
circulation model (GCM) and the possible use of a three-dimensional
variational assimilation (3D-Var) scheme. Two different kinds of severe
hydro-meteorological events that affected the Calabria region (southern Italy)
in 2015 are analysed using the WRF-Hydro atmosphere–hydrology modelling system
in its uncoupled version. Both of the events are modelled using the
0.25∘ resolution global forecasting system (GFS) and the
16 km resolution integrated forecasting system (IFS) initial and lateral
atmospheric boundary conditions, which are from the European Centre for
Medium-Range Weather Forecasts (ECMWF), applying the WRF mesoscale model for the
dynamical downscaling. For the IFS-driven forecasts, the effects of the
3D-Var scheme are also analysed. Finally, native initial and lower boundary SST
data are replaced with data from the Medspiration project by Institut Français de Recherche pour L'Exploitation
de la Mer (IFREMER)/Centre European Remote Sensing d'Archivage et de
Traitement (CERSAT),
which have a 24 h time resolution and a 2.2 km spatial resolution.
Precipitation estimates are compared with both ground-based and radar data,
as well as discharge estimates with stream gauging stations' data. Overall,
the experiments highlight that the added value of high-resolution SST
representation can be hidden by other more relevant sources of uncertainty,
especially the choice of the general circulation model providing the boundary
conditions. Nevertheless, in most cases, high-resolution SST fields show a
non-negligible impact on the simulation of the atmospheric boundary layer
processes, modifying flow dynamics and/or the amount of precipitated water; thus, this emphasizes the fact that uncertainty in SST representation should be duly
taken into account in operational forecasting in coastal areas.
THE GODAE HIGH-RESOLUTION SEA SURFACE TEMPERATURE PILOT PROJECT
