Hydro-geological hazard in Italy as Mapped by the local authorities

A friend gave pointed out to me this morning this map of hydrogeological hazards in Italy, as produced by the local authorities and collected by the Italian Ministry of Italy.  The full map at higher resolution (1.4 Mb) can be retrieved here (I think it is public and can be found somewhere in the Environmental Ministry of Italy). "Carta delle aree ad alta criticita' idrogeologica" means: maps of the area with the highest potential hazards. Red are landslides, blue are flooding, green snow avalanches hazards.

Well, some parts of Italy (as my Province of Trento) are very red and full of hazard. Some others (same hydrological and geological conditions, as the Province of Bolzano and Province of Belluno) are white: almost no hazard at all. (I tend to support the idea, since I was involved in part of its construction, that the hazard map of Trentino was produced with state of art techniques. But I also know that officiers of the other Provinces are also rigorous people. Then ?). The case of Emilia Romagna is also perfect example of this partition.  The Apennines in Emilia (under the Authority of River Po ?) are really red.  The Apennines in Romagna (under the river Authority of Reno River ?) are almost white.
Why these differences ? Different techniques of mapping ? Different "political choices" ?  Different stage of production of the maps (did all really made it) ?

Who knows can give me a clue ?