| Northern Italy is frequently affected by severe precipitation
conditions often inducing flood events with associated loss of
properties, damages and casualties. The capability of correctly
forecast these events, strongly required for an efficient support to
civil protection actions, is still nowadays a challenge. This
difficulty is also related with the complex structure of the
precipitation field in the Alpine area and, more generally, over the
Italian territory. Recently a new generation of non-hydrostatic
meteorological models, suitable to be used at very high spatial
resolution, has been developed.
In this paper the performance of the non-hydrostatic
Lokal Modell developed by the COSMO Consortium, is analysed with
regard to a couple of intense precipitation events occurred in the
Piemonte region in Northern Italy. These events were selected among
the reference cases of the Hydroptimet/INTERREG IIIB project.
LM run at the operational resolution of 7km provides a good
forecast of the general rain structure, with an unsatisfactory
representation of the precipitation distribution across the mountain
ranges. It is shown that the inclusion of
the new prognostic equations for cloud ice, rain and snow produces a
remarkable improvement, reducing the precipitation in the upwind
side and extending the intense rainfall area to the downwind
side. The unrealistic maxima are decreased towards observed values.
The use of very high horizontal resolution (2.8 km) improves the
general shape of the precipitation field in the flat area of the
Piemonte region but, keeping active the moist convection scheme,
sparse and more intense rainfall peaks are produced. When convective
precipitation is not parametrised but explicitly represented by the
model, this negative effect is removed. |