In recent years, numerous studies have shown a growing concern about the effects of climate change on the hydrological cycle and hydrological extremes. In particular, statistical analyses on either long hydrological series or modelled data show conflicting trends in different areas of Europe. In addition, the absence of continuous observations and the significant alterations experienced by some watersheds makes difficult to quantify the effects of climate change. These critical issues are particularly felt in Southern Italy where hydrometric monitoring is often discontinuous, updated flow rating curves rarely exist, and territories underwent significant anthropogenic transformations. The present work aims to update flood time-series in Southern Italy, using direct and indirect measurements, over the period 1920-2021. The numerous missing data were reconstructed by means of specially defined flood rating curve or by using daily flow rates to derive equivalent flood flows through the empirical function by Fuller. The obtained series were, then, analysed using the nonparametric Mann-Kendall test in order to detect possible trends. The results of the present study provide preliminary indications of flood trends over the last 50 years in Southern Italy by integrating an information gap regarding this phenomenon and its dynamics.

1. Italian Conference on Integrated River Basin Management (ICIRBM 2023) – 44th Edition
22-23 June 2023
UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY
Salvatore Manfreda1, Manuele Messina1, Angelo Avino1, Teresa Pizzolla2, Rocco Bonelli3, Luciana Giuzio3,
Vincenzo Totaro4, Vito Iacobellis4, Mauro Fiorentino2, Vera Corbelli3
1 Università degli Studi di Napoli Federico II, Dipartimento di Ingegneria Civile, Edile e Ambientale, Italia
2 Università degli Studi della Basilicata, Dipartimento delle Culture Europee e del Mediterraneo, Italia
3 Autorità di bacino distrettuale dell'Appennino Meridionale, 81100 Caserta, Italia
4 Politecnico di Bari, Dipartimento di Ingegneria Civile, Ambientale, del Territorio, Edile e di Chimica, 70125 Bari, Italia

2. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
2/19
Challenges of the Southern Italy in Water
Resources
• Climate change is altering hydrological forcings, affecting both water resource
availability and extreme events.
• Limited availability of continuous time-series and update flow rating curves.
• Existing infrastructure requires significant maintenance interventions are obsolete.
• Anthropogenic pressure and impermeabilization require specific attention for the
characterization of hydrological response at local scale.
1984 2022

3. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
3/19
“Global and Regional Increase of Precipitation Extremes
under Global Warming”
Papalexiou e Montanari, WRR, 2019
“Observed heavy precipitation increase
confirms theory and early models”
Fischer e Knutti, NCC, 2016
u Trends of increasing annual precipitation can be observed in
regions at mid to high latitudes, while a decrease in
precipitation is observed in the Mediterranean region at mid to
low latitudes.
u There has been a general increase in the frequency and
intensity of extreme precipitation events in recent decades.
The most rainy days are
becoming more frequent, at
the expense of days with
weak or no precipitation.
There is a trend of
increasing both the
intensity and frequency of
precipitation.
Framing the problem at the global scale

4. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
4/19
Mertz et al., (2021)
Trends in Flood
Observations
u Number of flood observation in
Southern Italy is a limiting factor
for this study.

5. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
5/19
Exceptional rainfall events in Southern Italy
Gargano, settembre 2014 (244mm in 24h)
Palermo, luglio 2020 (134mm in 2h)
Rossano Calabro, agosto 2015
(160mm in 4h, 408mm in 19h)
Matera, novembre 2019 (115mm in 9h)
Vibo Valentia, luglio 2006 (190mm in 2h)
Sarno, maggio 1998 (300mm in 72h)
Messina, ottobre 2009 (500mm in 24h)
Napoli Nord, ottobre 2018 (50mm in <1h)
Catania, ottobre 2021 (603mm in 72h)
Number of events observed suggests that
the frequency of extreme events triggered
by precipitation, such as landslides, river
and rainfall floods, has increased, leading
to problems for societies, natural
ecosystems, and productive activities.

6. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
6/19
Collection of hourly rainfall data in Southern
Italy for the period 1970-2020

7. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
7/19
Spatial representation of the detected trends using
the at-site Mann-Kendall (MK) test
Appennino Campano, area al confine
tra Molise, Campania e Puglia
Altopiano centrale del Molise e Parco
Regionale del Matese, al confine tra
Campania e Molise
Appennino Calabro, dall’altopiano della
Sila fino all’Aspromonte
Appennino Lucano, al confine tra
Basilicata e Campania
1h 6h
3h 12h 24h

8. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
8/19
Publication n. 17 Flood Peaks
Hydrological
Yearbooks (Part II)
Annual maximum values of the
average daily discharges, the
flow rating curves of the year
Civil Protection
water level measurements
from 1994 to 2021
Sources of Data
0
20
40
60
80
100
1920
1924
1928
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1985
1989
1993
1997
2001
2005
2009
2013
2017
2021
Total
Number
of
Stations
year
Monitoring Network in Campania
Misure Idrometriche Misure di levello e di portata
Since 1994, monitoring activities
have been limited to only
measuring levels that are useful
for real-time alert purposes, but
less useful for long-term
forecasting purposes.

9. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
9/19
Only 42 of these 181 hydrometric stations are the same of the SIMN network. Moreover, only 81% of these
42 stations have flow measurements for less than 50 years between 1920 and 2021 (database
completeness: 36%).
For Puglia, flow data is available until 2021 and published in the Hydrological Yearbooks.
Monitoring network in Southern Italy
The current
hydrometric
monitoring network
consists of 181 stations
distributed as follows :
u Campania: 55
u Lazio: 17
u Abruzzo: 2
u Molise: 1
u Puglia: 40
u Basilicata: 27
u Calabria: 39
Station Data Availability
8 >50%
22 25% - 50%
12 <25%
Actual Network Network of the ex SIMN still working

10. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
10/19
Sezione descrittiva
Nome stazione
Volturno a Cancello
Arnone (P.Garibaldi)
Regione Campania
Bacino Volturno
Periodo con misure 1931-1970
Area permeabile (%) 53
Area - P17 [kmq] 5558
Deflussomed,anno [mm] 583
Afflussomed,anno [mm] 1173
Qmax [m3/s] 1760
Hmax [m] 7.4
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1931
1934
1937
1940
1943
1946
1949
1952
1955
1958
1961
1964
1967
1970
1973
1976
1979
1983
1986
1989
1992
1995
1998
2001
2004
2007
2010
2013
2016
2019
2022
Portate
massime
[m
3
/s]
Anni R0
The available peak flow data for this station
only goes up until 1970.
Application on the Volturno at Cancello Arnone

11. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
11/19
Methods for estimating peak flow discharges.
𝑄!"# = 𝑄!$% # 1 + 2.66 # 𝐴&"'()*
+,..
(Fuller, 1914)
𝑄 = 𝑎 # 𝐻 − ℎ,
& (Herschy, 1985)
Method I
Method II
Fuller (1914)
Flood Rating Curve
Flood Rating Curve
Stable cross-section hypothesis: for high flow values, the floodplain
areas of the cross-section are also involved in the discharge, whose
geometry varies little over time (Claps et al., 2003).
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 1 2 3 4 5 6 7 8
Discharge
[m
3
/s]
H [m]
Cancello Arnone on the Volturno River
Dati Storici

12. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
12/19
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 1 2 3 4 5 6 7 8
Discharge
[m
3
/s]
H [m]
Flood Rating Curve - Volturno a Cancello Arnone
Dati Storici FRC Numerica FloodRating Curve
Method II
0
1
10
100
1000
10000
100000
0.1 1 10
Portata
[m
3
/s]
Altezza idrica [m]
The parameters of the flood discharge rating curve were
obtained by interpolating between pairs of historical
values of peak flow and maximum water level.
Application on the Volturno at Cancello Arnone
The numerical discharge rating curves, obtained using HEC-RAS
software, show a consistent trend with the flood stage-
discharge relationships.
For high water level values, the annual discharge rating
curves are aligned.

13. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
13/19
0
500
1000
1500
2000
2500
1931
1933
1935
1937
1939
1941
1943
1945
1947
1949
1951
1953
1955
1957
1959
1961
1963
1965
1967
1969
1971
1973
1975
1977
1979
1981
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
2018
2020
2022
Massimi
annuali
portate
al
colmo
di
iena
[m
3
/s]
Anni
R0 R1 R2
Annual peak flows collected in
Publications No. 17 and used to
build the Flood Rating Curve (R0)
Annual peak flows derived from the annual
maximum of daily mean flows (collected in
the Hydrological Annals), using the Method
I (R1)
Annual peak flows derived from the annual
maximum water levels (collected by the
Civil Protection Agency) using the Flood
Rating Curve (Method II) (R2)
Data Total number mean [m3/s]
Dev. Stnd.
[m3/s]
CV [-] Skewness [-]
R0 31 1115 283 0.25 0.517
R1 22 1082 373 0.34 0.267
R2 20 1050 525 0.50 0.080
Application on the Volturno at Cancello Arnone

14. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
14/19
Stazione Regione
E[Q]
(m3/s)
Flood Rating Curve MAPE –
FRC
(-)
RMSE -
FRC
(m3/s)
RMSE -
Fuller
(m3/s)
a b h0 R2
Cancello Arnone Campania 1115 17.37 2.3 0.054 0.81 0.08 111 110
Ponte Annibale Campania 1422 33.05 2 0.046 0.74 0.15 265 -
Amorosi Campania 651 35.55 2.18 0 0.7 0.2 151 103
Contursi Campania 229 52.69 1.41 0.98 0.69 0.25 104 108
Scafa di Persano Campania 872 62.62 2.08 0 0.92 0.09 82 236
Albanella Campania 1225 4.44 2.87 0 0.84 0.18 281 451
Montella Campania 52 7.86 1.87 0 0.57 0.17 16 18
Apice Campania 333 129.23 1.18 0.9 0.79 0.28 89 135
Solopaca Campania 995 15.15 2.2 0 0.97 0.1 95 323
Casalvelino Campania 261 12.65 1.79 0 0.91 0.08 23 105
Pago Veiano Campania 196 62.94 1.83 0 0.58 0.3 60 66
Paduli Campania 201 12.7 2.44 0 0.73 0.45 69 -
Sora Lazio 169 68.72 1.4 0.49 0.95 0.1 30 44
Isola Liri Lazio 175 80.21 1.47 0.05 0.77 0.22 68 -
Ceccano Lazio 263 9.4 2.45 1.22 0.77 0.07 50 -
P.te Sant'Ambrogio Lazio 912 67.84 1.57 0 0.76 0.06 75 -
Suio (San Castrese) Lazio 909 0.02 1.41 0 0.71 0.14 104 -
S.S. 106 Basilicata 506 1.83 3.35 0 0.59 0.47 323 288
Episcopia-Pizzutello Basilicata 238 36.25 1.45 0 0.76 0.19 68 107
Pie di Borgo Calabria 233 54.35 1.66 0 0.7 0.26 69 -
Razzona Calabria 76 12.11 2.08 0 0.69 0.36 29 -
Camerata Calabria 74 12.84 2.71 0.19 0.75 0.24 21 -
Parameters of the
flood discharge rating
curve according to the
Herschy expression,
and error indices
related to the two
reconstruction
methods (FRC and
Fuller's method).
Reconstruction methods results

15. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
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Kolmogorov-Smirnov statistical tests (in the two-
sample version) and the Mann-Kendall trend test
The two methodologies have
allowed for the reconstruction
of a total of 600 new peak
flow values, which are added
to the 597 available historical
measurements during the VAPI
era.
The Kolmogorov-Smirnov test (H-
KS) was performed by comparing
the reconstructed data (R1 and
R2) and the original series (R0).
Additionally, the results of the
Mann-Kendall test (H-MK) and
the estimation of Sen's slope are
provided (applied to the
complete series).
*significance at 5%
Stazione Regione
Area
[kmq]
Num.
R0
Num.
R1
Num.
R2
TOT
Periodo di
Riferimento
H-KS (R0-R2)
(a = 5%)*
H-KS (R0-R1)
(a = 5%)*
H-MK
(a = 5%)*
Sen’s
Slope
Cancello Arnone Campania 5558 31 22 20 73 1925-2021 0 0 No trend -1.00
Ponte Annibale Campania 5442 43 0 20 63 1915-2021 0 - No trend 2.72
Amorosi Campania 2015 41 10 27 78 1931-2021 1 1 Si trend -3.45
Contursi Campania 329 32 14 27 73 1932-2021 0 1 No trend -0.89
Scafa di Persano Campania 2396 13 4 27 44 1929-2021 1 0 Si trend 14.07
Albanella Campania 3235 41 16 27 84 1929-2021 0 0 No trend 2.98
Montella Campania 123 45 14 24 83 1931-2021 1 0 Si trend -0.18
Apice Campania 533 38 0 27 65 1933-2021 1 - Si trend -3.02
Solopaca Campania 2966 15 8 27 50 1965-2021 1 0 Si trend -13.73
Casalvelino Campania 280 18 16 17 51 1961-2021 1 1 Si trend -5.19
Pago Veiano Campania 557 18 6 14 38 1958-2021 1 0 Si trend 7.38
Paduli Campania 675 16 0 27 43 1954-2021 0 - No trend 0.00
Sora Lazio 1272 41 10 26 77 1929-2021 0 0 No trend -0.51
Isola Liri Lazio 1410 25 0 18 43 1929-2021 1 - Si trend 28.84
Ceccano Lazio 923 19 0 27 46 1959-2021 1 - Si trend -10.21
P.te Sant'Ambrogio Lazio 3500 12 0 20 32 1929-2021 0 - No trend -4.37
S.S. 106 Basilicata 2743 19 15 22 56 1933-2021 0 - Si trend 18.02
Episcopia-Pizzutello Basilicata 233 27 21 20 68 1925-2021 1 - No trend -0.84
Piè di Borgo Calabria 279 24 2 6 32 1927-2020 0 - No trend -0.89
Razzona Calabria 116 50 6 6 62 1927-2020 0 - No trend 0.02
Camerata Calabria 303 29 1 6 36 1928-2020 1 - Si trend 1.80

16. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
16/19
Stazione Regione
Area
[kmq]
Num. R0
Periodo di
Riferimento
H-MK
(a = 5%)*
Sen’s
Slope
S.Samuele di Cafiero Puglia 2716 81 1929-2020 Si trend -6.00
Cairano Puglia 272 30 1963-1994 Si trend -5.95
P.te sotto Atella Puglia 158 71 1934-2020 No trend 0.29
Monteverde Puglia 1028 60 1956-2020 Si trend -7.07
Rocchetta S.Antonio Puglia 1120 22 1926-1952 No trend 18.40
P.te Vecchio Rapolla Puglia 124 56 1952-2020 No trend -0.20
P.te SS 168 Puglia 29.5 31 1973-2012 Si trend 0.44
P.te Ferroviario Puglia 201 35 1973-2020 No trend 0.27
P.te S.Angelo Puglia 261 34 1929-1971 No trend 0.52
Carapelle Puglia 720 36 1935-1980 No trend -2.29
P.te Vecchio Ordona Puglia 506 35 1986-2020 No trend 0.46
Incoronata Puglia 657 80 1928-2020 No trend -1.22
S.Vincenzo Puglia 86 36 1967-2012 No trend -0.49
P.te Foggia-S.Severo Puglia 256 62 1935-2015 Si trend -0.87
P.te Troia Lucera Puglia 94 56 1965-2020 Si trend -2.69
Casanova Puglia 43.1 50 1965-2020 Si trend -1.63
P.te Lucera-Motta Puglia 52.3 46 1965-2020 No trend -0.44
P.te Foggia -S.Severo Puglia 463 66 1933-2020 No trend 0.61
P.te Lucera-Torremaggiore (1) Puglia 54 33 1943-2020 No trend -0.87
P.te Lucera-Torremaggiore (2) Puglia 59 43 1948-2020 No trend 0.18
The results of the Mann-Kendall test (H-
MK) and the estimation of Sen's slope are
reported (applied to the complete series).
*significance at 5%
The Mann-Kendall trend test

17. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
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Flood trends derived on the reconstructed data
Station Trend
6 Increaseing
24 No trend
12 Decrising
Station Region Area [kmq] Sen’s Slope
Scafa di Persano Campania 2396 14.07
Pago Veiano Campania 557 7.38
Isola Liri Lazio 1410 28.84
S.S. 106 Basilicata 2743 18.02
Camerata Calabria 303 1.8
P.te SS 168 Puglia 29.5 0.44
Station Region Area [kmq] Sen’s Slope
Amorosi Campania 2015 -3.45
Montella Campania 123 -0.18
Apice Campania 533 -3.02
Solopaca Campania 2966 -13.73
Casalvelino Campania 280 -5.19
Ceccano Lazio 923 -10.21
S.Samuele di Cafiero Puglia 2716 -6
Cairano Puglia 272 -5.95
Monteverde Puglia 1028 -7.07
P.te Foggia-S.Severo Puglia 256 -0.87
P.te Troia Lucera Puglia 94 -2.69
Casanova Puglia 43.1 -1.63
POSITIVE TREND
NEGATIVE TREND

18. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
18/19 u We tried to overcome a critical lack of flood observations over southern Italy.
u Two reconstruction methods have been used including the flood rating curves
(FRC), which can serve as a crucial resource for Civil Protection agencies.
u The new dataset, composed by three groups of data (R0, R1, R2), allowed to update
flood statistics.
u There is a considerable heterogeneity in the dynamics of floods, with a noteworthy
number of stations exhibiting negative trends.
u It is important to note that a negative trend does not necessarily indicate a
reduction of hazards. Recent time-series also exhibit greater variability compared
to the past, which could potentially impact flood severity. Thus, it is essential to
consider the potential implications of increased variability alongside the observed
negative trends.
Conclusions

19. UPDATING FLOOD ANNUAL MAXIMA IN SOUTHERN ITALY – Manfreda et al. (2023)
19/19 Thanks…
Fontana del Sebeto di via Caracciolo