All these tools and models provide meteorological data and information which are needed to: the Regional Meteorological Bulletin, notifications of Adverse Weather Conditions, forecasting of short-term events to evaluate conditions of criticality. The Functional Centre transmits the Regional Meteorological Bulletin, for civil defence purposes, to the Unified Regional Operations Room of the Civil defence (SORU), which forwards it to local and regional authorities. The Functional Centre, considers the Meteorological Daily Bulletin issued by the Department of Civil defence, its Regional Meteorological Bulletin and, eventually, other additional information to issue a Regional Notice of Adverse Weather Conditions whenever there is the possibility of occurrence of critical conditions due to heavy meteorological events (rainfalls, wind, temperature variations, rough sea). If the meteorological events refer to rainfall, a Regional Notice of Adverse Weather Conditions for hydrogeological and hydraulic risks is issued. With the issuance of the Notice of Adverse Weather Conditions, the Functional Centre states the possible level of criticality, the type of events, the risk scenarios expected. The Notice of Adverse Weather Conditions is issued normally by 14:00 and has minimum validity of 24 hours.

In general, the level of criticality for each Alert Zone is established taking into account the results of the meteorological analysis and the thresholds exceedance of precursors of criticality. The level of criticality ORDINARY is issued, in an Alert Zone, if the following conditions exist: the Notice of Adverse Weather Conditions predicts significant rainfall events for the following 24 hours; based on the results of LAMI model, one of the precursors of criticality exceed the threshold value corresponding to the ordinary condition criticality. The level of MODERATE is issued, in an Alert Zone, if the following conditions exist: the Notice of Adverse Weather Conditions predicts heavy rainfall events; based on the results of LAMI model, one of the precursors of criticality exceed the threshold value corresponding to the moderate condition criticality. The level of HIGH is issued, in an Alert Zone, if the following conditions exist: the Notice of Adverse Weather Conditions predicts heavy rainfall events; based on the results of LAMI model, one of the precursors of criticality exceed the threshold value corresponding to the high condition of criticality..

Monitoring phase

In Campania hydraulic and hydrogeological events induced by heavy rainfall typically refer to debris flows, earth flows in pyroclastic soils (Varnes 1978), shallow landslides, hyper-concentrated flows (Coussot and Meunier 1996), floods, localized floods for embankment failures, erosion by overland flow.

The D.P.G.R. n. 299/05 differentiates among six classes of critical rainfall events, by considering the characteristics of the hydrographical basins as follows:

• heavy rainfall events in time intervals of 0-6 hours that can generate an hydraulic crisis in basins having areas smaller than 100 km2 (including urban drainage areas);

• II. heavy rainfall events in time intervals lasting 3-12 hours, which can generate an hydraulic crisis in basins having areas between 100 km2 and 500 km2;

• III. heavy rainfall events in time intervals lasting 6-24 hours, which can generate an hydraulic crisis in basins having areas from 500 km2 to 2000 km2

• IV. heavy rainfall events in time intervals lasting 12-48 hours, which can generate an hydraulic crisis in basins having areas between 2’000 km2 and 5’000 km2;

• V. heavy rainfall events in time intervals of 24-48 hours, which can generate an hydraulical crisis in proximity of the mouth of the Volturno river (catchment larger than 5’000 km2);

• VI. heavy rainfall events in time intervals lasting 24-72 hours, considered as critical for the occurrence of shallow landslides and debris flows.

Taking into account the previous classification, for each Municipality one or more classes of risk in relation to the type of rainfall event can be defined:

• Class I. municipalities with hydraulic risk territories included in catchments whose size is smaller than 100 km2;

• Class II. municipalities with hydraulic risk territories included in catchments whose size is between 100 and 500 km2;

• Class III. municipalities with hydraulic risk territories included in catchments whose size is between 500 and 2,000 km2;

• Class IV. municipalities with hydraulic risk territories included in catchments whose size is between 2000 and 5000 km2;

• Class V. municipalities with hydraulic risk territories included in catchments whose size is larger than 5000 km2;

• Class VI. municipalities with territories at risk for the occurrence of fast slope movements.

All municipalities belong to class I, which means that they can potentially experience a crisis situation for a flood in a small basin (including urban catchment). The classes II, III, IV and V have been assigned to municipalities with areas at risk included in catchments bigger than 100 km2. The class VI, the only class of interest for this research, includes 212 municipalities of the Campania region deemed susceptible to fast slope movements after the disastrous landslides which occurred in Sarno in 1998 (Cascini 2004) plus municipalities in hilly and mountainous areas for which at least one landslide has been recorded in the AVI database CNR-GNDCI. An Annex to D.P.G.R. 299/2005 reports a table assigning the class of risk per each Municipality of the Campania region as shown in figure 4.9.

Rainfall precursors are, also in this phase, distinguished in local and areal precursors. Local precursors are defined as the heights of rainfall measured individually by each pluviometer. While the areal precursors are defined as the average heights of rainfall calculated in the catchment, as measured by several rain gauges of the monitoring network. For each risk class the following rainfall precursors have been considered:

• Class I: local precursors at time intervals of 1, 3, 6 hours;

• Class II: areal precursors at time intervals of  3, 6, 12 hours;

• Class III: areal precursors at time intervals of 6, 12, 24 hours;

• Class IV: areal precursors at time intervals of 12, 24, 48 hours;

• Class V: areal precursors at time intervals of 24, 48 hours; 

• Class VI: local precursors at time intervals of 24, 48, 72 hours;

For each type of rainfall precursor and time interval, threshold values have been obtained from statistical analysis on available historical rainfall series. For each Municipality, belonging to risk class I and VI, a single pluviometer has been chosen as reference and its height of rainfall used as local precursor. On the contrary for each Municipality of classes II, III, IV, V a reference catchment has been assigned and the mean height of rainfall over the carchment is used as areal precursor. Independently of the type and time interval of the rainfall precursor, three different threshold values have been determined based on the following return periods of rainfall: 2, 5, 10 years. The three different values obtained for each type of precursor correspond to three levels of warning for hydrogeological and/or hydraulic risk assigned, for each municipality of the Campania Region, as follows: attention, pre-alarm, alarm. In particular, the attention level is activated when the rainfall precursors exceed the threshold value corresponding to a return period of 2 years. The attention level is also issued by regional Civil defence on the basis of Notice of Criticalities emitted by the Functional Centre with if "moderate" or "high" critical conditions exist in at least one of the 8 alert zones. Pre-alarm status for hydrogeological risk is activated only as a function of rainfall precursors and in particular, if they exceed the pre-alarm threshold values ​​(return period of 5 years). Finally, the Alarm level for hydrogeological risk is activated if rainfall precursors exceed the alarm threshold values ​​ corresponding to a return period of 10 years.

Rainfall precursors are, also in this phase, distinguished in local and areal precursors. Local precursors are defined as the heights of rainfall measured individually by each pluviometer. While the areal precursors are defined as the average heights of rainfall calculated in the catchment, as measured by several rain gauges of the monitoring network. For each risk class the following rainfall precursors have been considered:

• Class I: local precursors at time intervals of 1, 3, 6 hours;

• Class II: areal precursors at time intervals of  3, 6, 12 hours;

• Class III: areal precursors at time intervals of 6, 12, 24 hours;

• Class IV: areal precursors at time intervals of 12, 24, 48 hours;

• Class V: areal precursors at time intervals of 24, 48 hours; 

• Class VI: local precursors at time intervals of 24, 48, 72 hours;

For each type of rainfall precursor and time interval, threshold values have been obtained from statistical analysis on available historical rainfall series. For each Municipality, belonging to risk class I and VI, a single pluviometer has been chosen as reference and its height of rainfall used as local precursor. On the contrary for each Municipality of classes II, III, IV, V a reference catchment has been assigned and the mean height of rainfall over the catchment is used as areal precursor. Independently of the type and time interval of the rainfall precursor, three different threshold values have been determined based on the following return periods of rainfall: 2, 5, 10 years. The three different values obtained for each type of precursor correspond to three levels of warning for hydrogeological and/or hydraulic risk assigned, for each municipality of the Campania Region, as follows: attention, pre-alarm, alarm. In particular, the attention level is activated when the rainfall precursors exceed the threshold value corresponding to a return period of 2 years. The attention level is also issued by regional Civil defence on the basis of Notice of Criticalities emitted by the Functional Centre with if "moderate" or "high" critical conditions exist in at least one of the 8 alert zones. Pre-alarm status for hydrogeological risk is activated only as a function of rainfall precursors and in particular, if they exceed the pre-alarm threshold values (return period of 5 years). Finally, the Alarm level for hydrogeological risk is activated if rainfall precursors exceed the alarm threshold values  corresponding to a return period of 10 years.

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1 The modelling

Six hydrogeological and hydraulic classes of risk are identified in the system at municipal level, each one associated to critical rainfall events of different duration. Among these classes, only the risk class named VI refers to landslide risk, in particular to the possible occurrence of fast slope movements; the other classes deal with hydraulic risks. To risk class VI are associated local precursors evaluated considering the cumulated rainfall at intervals of 24, 48 and 72 hours. The threshold values selected for the activation of the warning states of attention, pre-alarm and alarm, have been estimated considering reference return periods equal to 2, 5 and 10 years, respectively. The rainfall thresholds of the warning model have been estimated for each pluviometer on the basis of statistical analyses on historical records of rainfall. Given the maximum annual rainfall aggregate at an assigned duration, X, its value XT related to the return period T, is defined by the following relationship:

XT=KTm(X)                                                                          (Eq. 2)

where: KT is a probabilistic growth factor, function of the return period T; m(X) is the average value of the distribution of the variable X.

The decisional algorithm therefore includes three rainfall thresholds (cumulated rainfall at 24, 48 and 72 hours) evaluated for three return periods (2, 5, 10 years) for each pluviometer. The thresholds, if exceeded, activate one of the three warning levels defined for the early warning system: attention, pre-alarm, alarm. Each municipality has a set of rainfall thresholds, which depend on the pluviometer to which they are associated.

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2 The warning strategy

The response of the regional civil protection on the territory of the Campania region is implemented through the following 3 alert levels for the hydrogeological and/or hydraulic risk: attention, warning, alarm. The attention level is issued by the Settore di Programmazione Interventi of the Civil Protection Agency when the level of criticality is "moderate" or "high" in at least one of the 8 zones of alert and, also, when the punctual or areal pluviometric precursors exceed the threshold values ​​of attention (return period of 2 years). The department may provide that the Centro Funzionale and the Operational Structure become operative H24. The warning level for hydrogeological risk is activated by the Settore di Programmazione Interventi of the Civil Protection Agency when the punctual or areal pluviometric precursors exceed the threshold values ​​of warning (return period of 5 years). Moreover, the warning level for hydraulic risk is also activated when hydrometric indicators exceed the ​​"ordinary" level.

The alarm level for hydrogeological risk is issued by the Settore di Programmazione Interventi of the Civil Protection Agency when the punctual or areal pluviometric precursors exceed the threshold value of alarm (return period of 10 years), taking into account the information from Engineers, Presidi Territoriali and Mayors. Moreover, the alarm level for hydraulic risk is also activated when hydrometric indicators exceed the ​​​​"extraordinary" level.

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2 The response strategy

An information system has been developed for the management in real time of the alert issued based on pluviometric precursors. The information system is connected to the storage system of rainfall data of the functional center. The system is able to process and display real-time values ​​of the precursors and alerts about the possibility of exceeding the threshold values. When a threshold value is exceeded, at the functional center is automatically highlighted the list of municipalities associated with the precursor and its alert level. This allows to quickly and effectively identifying the competent authorities of the territory to which communicate the state of alert. The information system is incorporated into the geographic information system operating at the Sala Operativa Regionale Unificata. Through the activity of “presidio territoriale”, the Sala Operativa Regionale Unificata of the Settore of Civil Protection, as made possible by its instrumental equipment and knowledge, monitors the evolution of critical phenomena in the area and notify to the Centro Funzionale, in relation to the single event in progress.

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References

Dpgr 299, 30 giugno 2005. Il Sistema di Allertamento Regionale per il rischio Idrogeologico e Idraulico ai fini di protezione civile, Campania, Italia.

Rossi F, Fiorentino M, Versace P (1984) Two component extreme value distribution for flood frequency analysis. Water Resour Res 20(2):847–856