The purpose of this activity is to update, validate, and develop meteorological and hydrological reanalysis datasets to support the national power system in identifying atmospheric and ground-based threats. The existing Meteorological Reanalysis Italian DAtaset (MERIDA) reanalysis products were updated to cover the most recent years and extended to a longer time period, so that a complete and up-to-date reanalysis dataset is available for a period of 20 years.

In addition, the development of new MERIDA reanalysis products continued in the present research year. In particular, the new MERIDA High RESolution (HRES) Optimal Interpolation (OI) reanalysis dataset was created by combining modeling information from the existing MERIDA HRES at 4km and interpolation of observed precipitation and temperature data from gauging stations in the Italian Regional Environmental Agencies (ARPA) regional network, via the OI technique, already used to create the MERIDA OI dataset.

Following the extension and development phase of the dataset, work was also done to validate the MERIDA reanalysis products (MERIDA, MERIDA OI, MERIDA HRES, MERIDA HRES OI, Atlante EOLico ItaliANo (AEOLIAN)), comparing, with the observed available, some of the variables of greatest interest for the study of atmospheric and ground-based threats, such as precipitation, temperature, and wind. Thanks to these analyses, it was possible to apply the reanalysis datasets for hydrometeorological hazard studies at the national scale and for the study of snow threat and sleeve load formation in wet snow conditions.

As part of the study of hydrogeological hazard, analyses of return times and probabilities of occurrence of extreme precipitation events were carried out from the MERIDA HRES OI reanalysis dataset, for the calculation of landslide and flood risk under isofrequency assumptions.

In addition, the implementation of the WRF-Hydro distributed hydrological model at the national scale has been initiated to create a hydrological reanalysis dataset at a resolution of about 200 meters over the whole of Italy, forced from the MERIDA HRES OI reanalyses, so as to allow a better description of the soil-atmosphere interaction and a complete representation of hydrological variables such as soil moisture, snowpack accumulation and melting, flow in streams, and water availability at the inlet to the main reservoirs.

Finally, from the point of view of the threat related to winter phenomena, from the atmospheric variables provided by the reanalyses, the study of sleeve accretion models under wet snow conditions was continued by extending the series of sleeve loads through 2021. Expected values of sleeve loads were derived for two conductors, predominantly used on overhead transmission and distribution power lines for significant return times for power grid planning.