  The Campi Flegrei volcanic field (Italy) poses very high risk to the highly
urbanized Neapolitan area. Eruptive history was dominated by explosive activity
producing pyroclastic currents (PDCs; (Proclastic Density Currents) ranging in
scale from localized base surges to regional flows. Here we apply probabilistic
numerical simulation approaches to produce PDC hazard maps, based on a
comprehensive spectrum of flow properties and vent locations. These maps and
provide all probable Volcanic Explosivity Index (VEI) scenarios from different
source vents in the caldera, relevant for risk management planning. For each
VEI scenario, we report the conditional probability for PDCs (i.e., the
probability for a given area to be affected by the passage of PDCs) and related
dynamic pressure. Model results indicate that PDCs from VEI<4 events would be
confined within the Campi Flegrei caldera, PDC propagation being impeded by the
northern and eastern caldera walls. Conversely, PDCs from VEI 4-5 events could
invade a wide area beyond the northern caldera rim, as well as part of the
Naples metropolitan area to the east. A major controlling factor of PDC
dispersal is represented by the location of the vent area. PDCs from the
potentially largest eruption scenarios (analogous to the ~15 ka, VEI 6
Neapolitan Yellow Tuff or even the ~39 ka, VEI 7 Campanian Ignimbrite extreme
event) would affect a large part of the Campanian Plain to the north and the
city of Naples to the east. Thus, in case of renewal of eruptive activity at
Campi Flegrei, up to 3 million people will be potentially exposed to volcanic
hazard, pointing out the urgency of an emergency plan. Considering the present
level of uncertainty in forecasting the future eruption type, size and location
we suggest that appropriate planning measures should face at least the VEI 5
reference scenario (at least 2 occurrences documented in the last 10 ka)
