**4.1 2003 event (23-25 January)**

The 2003 heavy rainfall event affected almost the entire region - but mostly the central and south-eastern part (Chieti and Pescara province and part of L'Aquila and Teramo) - for almost 72 h.

The monthly rainfall analysis shows January 2003 values very much higher than the average historical values, ranging from 50 mm to 150 mm (Fig. 3a), which in some cases is up to 3 times. Several values are >250 mm and some are > 300 mm, up to a maximum recorded value of 388 mm (Salle station; Fig. 3a). These values are close or in some cases higher than the previous historical January maximum values (Fig. 3a). Moreover, the rainfall occurred after a December which had already been very rainy, with a two month precipitation value up to 60% or even 80% of the average annual precipitation (D'ALESSANDRO et al., 2004).

The daily rainfall is high but less than it was for the 2007 and 2011 events. The higher values - up to > 120 mm - are recorded along the front of the chain, in the Maiella area (Salle, Popoli; Fig. 4a).

Geomorphological Instability Triggered

mm/h in the hilly area (Nereto station; Fig. 5b).

mm) and occurring after two months of low rainfall.

**4.3 2011 event (1-2 March)** 

(22-26 h).

5000 years.

recurrence interval is estimated to be between 1000 to 5000 years.

**4.2 2007 event (6-7 October)** 

for a short time (14-16 h).

summer period.

4b).

by Heavy Rainfall: Examples in the Abruzzi Region (Central Italy) 51

The 2007 heavy rainfall event affected a local area in the northern Abruzzo (hilly and coastal Tortoreto area within the Teramo province, between the Salinello and Vibrata rivers; Fig. 2)

The monthly rainfall was higher than the average historical values, ranging from 60 mm to 80 mm (Fig. 3b). The values are >150 mm and some are > 200 mm, up to the maximum recorded value of 291 mm (Nereto station; Fig. 3b). These values are close to the previous historical October maximum values (Fig. 3b). This event occurred after a relatively dry

The daily rainfall in this case was very intense, with values ~100 mm in the hilly area close to the coast, up to a maximum of 205 mm (Nereto station; Fig. 4b), even when of a short event duration. Along the coast, the recorded daily precipitation is around 60-80 mm (Fig.

The hourly rainfall was very high, with values from 10 mm/h in the coastal area to 40

Taking into account the short duration of the event (14-16 h), the cumulative rainfall during this time interval was also very high, with values from 60-80 mm in the coastal area to 220 mm in the hilly area (Nereto station; Fig. 5b). At the Nereto station, the 24h precipitation

In summary, the 2007 event is an extreme event (for the Mediterranean environment), with a high intensity (10-40 mm/hr, up to >200 mm/day), a high cumulative rainfall (up to 220

The 2011 heavy rainfall event affected a provincial area (hilly and coastal Teramo area between Vomano, Tordino, Salinello and Vibrata rivers; Fig. 2) for a moderately short time

The monthly rainfall was very high compared to the average March values. The values are between 150 mm and 250 mm, up to the maximum recorded values of 282 mm (Nereto station; Fig. 3c) and 291 mm (Fano a Corno station; Fig. 3c). This event occurred after a

The daily rainfall was very intense - as in the 2007 event - with values of ~100-120 mm/d in

The hourly rainfall was again very high, with values around 15-20 mm/h in the coastal area,

Taking into account the duration of the event (22-26 h), the cumulative rainfall during this time was again very high, with values from 100-130 mm at most of the stations up to a maximum of 211 mm in the hilly area (Nereto station; Fig. 5c). Also, in this case, at the Nereto station the 24h precipitation recurrence interval is estimated to be between 1000 to

moderately humid winter period comparable with the historical average values.

and up to 35 mm/h in the hilly area (Pineto and Nereto stations; Fig. 5c).

the hilly area close to the coast, up to a maximum of 180 mm (Nereto station; Fig. 4c).

Hourly rainfall is not as critical as the daily, monthly and event rainfall are. The values do not exceed 9-10 mm/h (Fig. 5a). With regard to the event rainfall, the values are critical, reaching - and in some cases exceeding - 200 mm in three days (Fig. 5a).

In summary, the 2003 event can be considered to be of moderate to high intensity (~10-15 mm/hr, 80-120 mm/day) but very long (72 h), with a high cumulative rainfall (up to >200 mm) which occurred after two months of high rainfall (up to 80% of the average annual rainfall).

Fig. 3. Monthly rainfall: a) January rainfall histogram for the Abruzzi area; from left to right, data from the pluviometric stations of the Chieti, Pescara, Teramo and L'Aquila provinces. For each station, the total January 2003 rainfall, previous historical maximum January rainfall (1920-1997) and previous average January rainfall (1920-1997) are compared (modified form D'Alessandro et al., 2004); b) October monthly rainfall in the Teramo province's hilly and coastal areas. Comparison of the total October 2007 rainfall, the previous historical maximum October rainfall (1920-2006) and the previous average January rainfall (1920-2006); c) Monthly and daily rainfall; d) 2011 January, February and March rainfall.

## **4.2 2007 event (6-7 October)**

50 Studies on Environmental and Applied Geomorphology

Hourly rainfall is not as critical as the daily, monthly and event rainfall are. The values do not exceed 9-10 mm/h (Fig. 5a). With regard to the event rainfall, the values are critical,

In summary, the 2003 event can be considered to be of moderate to high intensity (~10-15 mm/hr, 80-120 mm/day) but very long (72 h), with a high cumulative rainfall (up to >200 mm) which occurred after two months of high rainfall (up to 80% of the average annual

Fig. 3. Monthly rainfall: a) January rainfall histogram for the Abruzzi area; from left to right, data from the pluviometric stations of the Chieti, Pescara, Teramo and L'Aquila provinces. For each station, the total January 2003 rainfall, previous historical maximum January rainfall (1920-1997) and previous average January rainfall (1920-1997) are compared (modified form D'Alessandro et al., 2004); b) October monthly rainfall in the Teramo province's hilly and coastal areas. Comparison of the total October 2007 rainfall, the

previous historical maximum October rainfall (1920-2006) and the previous average January rainfall (1920-2006); c) Monthly and daily rainfall; d) 2011 January, February and March

reaching - and in some cases exceeding - 200 mm in three days (Fig. 5a).

rainfall).

rainfall.

The 2007 heavy rainfall event affected a local area in the northern Abruzzo (hilly and coastal Tortoreto area within the Teramo province, between the Salinello and Vibrata rivers; Fig. 2) for a short time (14-16 h).

The monthly rainfall was higher than the average historical values, ranging from 60 mm to 80 mm (Fig. 3b). The values are >150 mm and some are > 200 mm, up to the maximum recorded value of 291 mm (Nereto station; Fig. 3b). These values are close to the previous historical October maximum values (Fig. 3b). This event occurred after a relatively dry summer period.

The daily rainfall in this case was very intense, with values ~100 mm in the hilly area close to the coast, up to a maximum of 205 mm (Nereto station; Fig. 4b), even when of a short event duration. Along the coast, the recorded daily precipitation is around 60-80 mm (Fig. 4b).

The hourly rainfall was very high, with values from 10 mm/h in the coastal area to 40 mm/h in the hilly area (Nereto station; Fig. 5b).

Taking into account the short duration of the event (14-16 h), the cumulative rainfall during this time interval was also very high, with values from 60-80 mm in the coastal area to 220 mm in the hilly area (Nereto station; Fig. 5b). At the Nereto station, the 24h precipitation recurrence interval is estimated to be between 1000 to 5000 years.

In summary, the 2007 event is an extreme event (for the Mediterranean environment), with a high intensity (10-40 mm/hr, up to >200 mm/day), a high cumulative rainfall (up to 220 mm) and occurring after two months of low rainfall.

## **4.3 2011 event (1-2 March)**

The 2011 heavy rainfall event affected a provincial area (hilly and coastal Teramo area between Vomano, Tordino, Salinello and Vibrata rivers; Fig. 2) for a moderately short time (22-26 h).

The monthly rainfall was very high compared to the average March values. The values are between 150 mm and 250 mm, up to the maximum recorded values of 282 mm (Nereto station; Fig. 3c) and 291 mm (Fano a Corno station; Fig. 3c). This event occurred after a moderately humid winter period comparable with the historical average values.

The daily rainfall was very intense - as in the 2007 event - with values of ~100-120 mm/d in the hilly area close to the coast, up to a maximum of 180 mm (Nereto station; Fig. 4c).

The hourly rainfall was again very high, with values around 15-20 mm/h in the coastal area, and up to 35 mm/h in the hilly area (Pineto and Nereto stations; Fig. 5c).

Taking into account the duration of the event (22-26 h), the cumulative rainfall during this time was again very high, with values from 100-130 mm at most of the stations up to a maximum of 211 mm in the hilly area (Nereto station; Fig. 5c). Also, in this case, at the Nereto station the 24h precipitation recurrence interval is estimated to be between 1000 to 5000 years.

Geomorphological Instability Triggered

**5.1 2003 event (23-25 January)** 

(Fig. 6; D'Alessandro et al., 2004).

by Heavy Rainfall: Examples in the Abruzzi Region (Central Italy) 53

Fig. 5. The hourly and cumulative rainfall occurring during the heavy rainfall events: a) on 23-25 January 2003 at the Salle (PE) station; b) on 7 October 2007 at the Nereto (TE) station; c) on 2 March 2011 at the Nereto (TE) station; d) on 2 March 2011 at the Pineto (TE) station.

**5. Geomorphological effects and landforms triggered by heavy rainfall events** 

At the end of January, according to the meteorological aspects of the event, outcropping lithologies and surface eluvial and colluvial covers were already very humid and - in almost water saturation conditions - had a strong susceptibility to slope instability. In these conditions, the occurrence of prolonged and intense precipitation on 23-25 January 2003 induced heavy flooding within the main alluvial plains (the rivers Sinello, Sangro, Trigno, Foro and Alento) and triggered ~1300 landslides ranging from the small to the very wide (mostly rapid earth flows and debris flows, secondary rock falls and rotational/translational sliding). The type and distribution of landslides were strictly controlled by the lithology and morphostructural setting and by the poorly vegetated landscape due to the winter season

The landslides on Quaternary continental deposits (7%) were mostly small flows and slides, located along the scarp edge of fluvial terraces or affecting the talus slopes in the mountain

In summary, the 2011 event is an extreme one (for the Mediterranean environment), although intermediate in respect of the previous ones: it affected a provincial area for a moderately short duration (22-26 h) with a high intensity (15-35 mm/h, up to >180 mm/d), high cumulative rainfall (up to 211 mm) and occurring after two months of moderate rainfall.

Fig. 4. Maximum daily rainfall occurred: a) on 23-25 January 2003; b) on 7 October 2007; c) on 2 March 2011.

In summary, the 2011 event is an extreme one (for the Mediterranean environment), although intermediate in respect of the previous ones: it affected a provincial area for a moderately short duration (22-26 h) with a high intensity (15-35 mm/h, up to >180 mm/d), high cumulative rainfall (up to 211 mm) and occurring after two months of moderate

Fig. 4. Maximum daily rainfall occurred: a) on 23-25 January 2003; b) on 7 October 2007; c)

rainfall.

on 2 March 2011.

Fig. 5. The hourly and cumulative rainfall occurring during the heavy rainfall events: a) on 23-25 January 2003 at the Salle (PE) station; b) on 7 October 2007 at the Nereto (TE) station; c) on 2 March 2011 at the Nereto (TE) station; d) on 2 March 2011 at the Pineto (TE) station.
