Geo-Hydrological Hazard and Urban Development in the Mediterranean Area: an Example from Genoa City (Italy) F

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 ff , and J. V. De Gra 2 2451 2452 , L. Turconi 1 ered from significant geo-hydrological events caus- ff , A. Sacchini 2 , F. Luino 1 Among the important topics analyzed in this paper are: (i) the meteorological char- The city of Genoa serves as a very interesting case-study for geo-hydrological risks. This discussion paper is/has beenSystem under Sciences review (NHESS). for Please the refer journal to Natural the Hazards corresponding and final Earth paper in NHESS if available. iTV UniversityDiSTAV, of Genoa, corso EuropaNational 26, Research 16132 Council, Genoa, Research Italy Institute for Geo-hydrological Protection, Strada delle California State University, M/S ST24, Fresno, CA 93740, USA acteristics of these events, (ii)most the significant changes periods in of the the rate urbanof of land the daily development territory precipitation, determining and above important all (iii) changes the on the hydrographic network. Abstract The Ligurian area has always su duced a general trend offor increasing risk the for narrowing the city. processmain Urbanization in is ones particularly and all notable in cross-sections thenarrowing of secondary of Genoa’s streams the that watercourses, sections flow bothto resulted directly in from both into the the industrial the Gulf increasing developmentand of demand (which Genoa. the for started The new growth initially spaces of atthan owing the the 200 Genoa 000 coastal population. at areas The the1970s of number modifying beginning Genoa), of the of inhabitants water therisk grew balance 19th in from of century an the fewer unacceptable tool basins way. a and peak increasing of the geo-hydrological over 800 000 in the Cloudbursts of few hours seempast; to that have causes a increase rainfall ofalarming intensity hydrometric values basically levels close of greater the to than watercourses the inurbanization that overflowing. the of quickly This the reach meteorological valley factor, floors added and to slopes growing located north of Genoa, has inevitably pro- 1 2 Cacce, 73, 101353 Turin, Italy Received: 3 March 2015 – Accepted: 19Correspondence March to: 2015 F. Faccini – ([email protected]) Published: and 10 F. April LuinoPublished 2015 ([email protected]) by Copernicus Publications on behalf of the European Geosciences Union. ing casualties and serious damage.coupled The with landform atmospheric peculiarities circulation are inhuman the autumn life, main and structures, causes winter this and hazard infrastructures.tan becoming Genoa area a city risk are and to commonly themany subject surrounding shallow to metropoli- landslides. heavy The rainfalland 15 that most November induces recent 2014, violent again rainfall causingtroubling flash events loss trend floods occurred of since human the and on lives beginning and 9–10 ofwith widespread the greater October damage. new frequency A century, than is in the the recurrence past. of such events Geo-hydrological hazard and urban development in the Mediterranean area: an example from Genoa City (Italy) F. Faccini Nat. Hazards Earth Syst. Sci.www.nat-hazards-earth-syst-sci-discuss.net/3/2451/2015/ Discuss., 3, 2451–2492, 2015 doi:10.5194/nhessd-3-2451-2015 © Author(s) 2015. CC Attribution 3.0 License. 5 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ected ected ff ff in which 2 areas that flow directly 2 ecting Italy. Within the Italian peninsula, ff and hosting a population of 1,5 million of erent areas and cause severe damage to ff 2 2454 2453 ered one of its most catastrophic flood events ff ect di . From W to E, they are San Michele, Sant’Antonio, ff 2 ; moving From W to E, they are Cerusa, Leiro, Branega, S. Pietro, Varenna, 2 The area of Genoa is characterized by a complex morphology determined by the In 7–8 October 1970 Genoa City su In this study, the authors examine the circumstances that led to an increased geo- Molinassi, Cantarena, San Pietro,nally, Priaruggia, there are Castagna, about Bagnara 10 and other Murcarolo. catchment Fi- with less than 1 km work consists of numeroustain steep a concentration and time shortthan of 4 watercourses less km that than an duringChiaravagna, hour. floods Polcevera, Ten Bisagno, catchments can Sturla have at- and anments Nervi range area in (Fig. of area 1). more from 1 Nine to other 4 km stream catch- Alpine–Apennine system which hosts2000 relief m, rapidly extending descending from towards peaks the between Ligurian 1000 Sea. and The resulting hydrographic net- urban development it ismore noteworthy concentrated that around population areas andcontinues with infrastructures exposed a are to locally more risk. uniquecal and combination This factors of favoring development meteorological, geo-hydrological climatic took hazardclimate and events. place hazard The geographi- and combination and growing of vulnerable urban theof conditions increasing have the made recent Genoa increase emblematic in flooding risk around the Mediterranean area. 2 Geographical settings of Genoa Since Middle Age, Genoaworld was a between very the importantmost Atlantic maritime important Ocean republic harbors and trading in allbetween China. both over Northern Today, Italy the Genoa Europe and and is Europetween the due home the Mediterranean to Ligurian to Sea. its Sea It one strategic andone serves of position important of as for the areas the a trade of transit ten the point metropolitan Po be- cities Valley. Consequently, of Genoa Italy is with an urban areainhabitants of distributed over in 500 km the2011). central sector of the Ligurian coastal arch (CityRailways, 600 000 inhabitants livearea (from covering Voltri to a Nervi) total within amount the of more 4000 km extensive metropolitan when an anticyclonicGenoa block city and generated the hinterland recurringof between 7 Voltri thunderstorm October and to the supercells early Bisagnolocations hours which Valley in of from 9 the the hit October Polcevera valley morning resulting (catchmentthe in “l” Municipality about in 900 flooded mm Fig. large in 1). urbanized onlyarea Most was areas 24 of h Genoa in streams in center a and some and very its creekin western in short the neighborhoods. time. Serious other The damage 20 also mostlocalities occurred municipalities a in in the the hinterland Genoaand were Stura province, between and the among Scrivia valley which Valleys. of Theindividuals. the fatalities Polcevera More most were and 44 Bisagno a recently, and streams significant thetook damaging evacuees place were hydro-geologic over in 2000 events 2010,and in 2011 heavy Genoa and socio-economic damages. 2014 city (October and November) causinghydrological several risk victims in Genoa city and in its immediate surroundings. By studying historic 1 Introduction From a geological andconsidered geomorphological a young point landscape ofTuritto, and 1997). view, a Geo-hydrological the very processes Italian “fragile” areslides, territory peninsula very debris (Almagià, common can 1907; in flows be Italy: Govi and and every flooding year land- a Genoa city mirrors theas 589 impacts BC of and geo-hydrological1452, characterized processes 1465, by 1582, documented significant 1746, as eventsfecting 1780, in Genoa early 1787, city 1404, since and 1407, the 1790. 1414, beginning Table 1416, of 2 the 1420, describes 19th century. severe events af- structures and infrastructures and oftenuments claim and human maps lives can (Luino, attest 2005). tophenomena Archival the and doc- widespread their areas frequency of extending thereports from peninsula some damaged to by of the this Roman the Age notable to recent present. events Table a 1 5 5 25 20 10 15 15 20 25 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent locations over the Ligurian ) located West of the historic am- ff 2 C) and widespread rainfall in all sea- ◦ ) and Chiaravagna Stream at Sestri Po- 2 ) flowing immediately on the East. Impor- 2 ected di ff 2456 2455 . The most recent of these events occurred on Novem- 1 − or 180 mm h ). 2 1 C (Cortemiglia, 2006). Overall, it is a humid temperate climate with limited − ◦ ) of Varenna Stream at Pegli (22 km C), temperate summers (average July 24 ◦ 2 The morphology of the Ligurian Gulf and the orographic barrier also contribute to Of particular importance during times when hot humid flows coming from Mediter- The coastal climate is characterized by short and temperate winters (average Jan- Following a practice widespread in in Liguria, many of these Genoan river beds From the meteorological point of view, the Genoa Gulf is characterized by a typical Gulf (Faccini et al.,500 2012) mm 6 causing h flash floodsber 2014 arising in from Genoa. rainfall Theserecent intensities years, phenomena especially of have the been last over two recurringPonente events that and in took particularly place 2010 in violent Varazze (Faccini in andBisagno Genoa-Sestri et Valley in al., 2011 2014), (Brandolini et Cinqueterre al., (Buzzi 2012) and et 2014. al., 2013)3 and Genoa- Previous research in the studyFlood area risk and methodological being approach theboth result considering: of two (i) factors, floodsthe hazard territory from and on the vulnerability, we the pointfrom analyzed basis the of them of point view observed of of climaticassessed view variations by the of historical and increase the comparison (ii) of territory of the ancient such modifications, land and above events vulnerability recent all in maps. increasing The urbanization present study de- ranean Sea are associatedperturbations, with are pre-frontal the situations great precedingMediterranean contrasts the basin between arrival and of the the Atlantic air airof masses mass these moving stationed from air over the2012). the masses Po warm These basin. triggers The supercells the convergence have development recently of a storm supercells (Silvestro et al., rainy events which may be verywhen intense Atlantic especially perturbations at the may(Bossolasco end be et of blocked the al., by summer 1971; or the Caredio autumn et European al., continental 1998; anticyclone Cevasco et al., 2010). mountain passes included the onestitudes, between between Savona 450 and and Genoa, 600 reachingthe ma.s.l. modest large (Fig. al- amounts 2). of This rainfalls(Sacchini typical distributed circulation et over is the al., responsible region 2012). for thunderstorm surrounding Similar supercells the between air Ligurian the masses Sea end contrasts of summer are and responsible autumn. for triggering of uary 8 tant urban areas are(27 also km located in thenente plain (11 km coastal basins of Leiro Stream at Voltri new narrow spaces roadseven homes have have been been realized. developed, parking areas and in some cases are culverted sometimes for long stretches, especially towards the mouth. On these sons with the maximum occurringaverage ranging in from autumn 1100 (150–200 mm toaround in 1300 16 mm October) (Table and 3) an and annual an annual average temperature circulation referred to as the(“Genua Genoa Low Tief” which is for alsoexisting Central known as cyclone Alps). a to Ligurian It the Depression then is south moves a of over the cyclone the Alpssion that Po over linked Valley forms the to (Sáez or the Gulf de arrivalGulf of intensifies Cámara of primarily Genoa, from et the in Ligurian the Atlantic al., a Sea autumn-winter perturbations 2011).As pre- and which behind A a spring the periods secondary consequence, Alps (Anagnostopoulou depres- conditions isMediterranean et formed al., of air on 2006). masses sharp the and thermodynamiccold cold contrast air air between masses masses hot over ofrected the humid continental by Po origin the Plain are Genoa and created. Low behind The toward the the mountainous center Ligurian of arc the Gulf, are where redi- they arrive through the dry season restricted to one or two summer months. into the old portsmall streams which define underlies floodplains the onlyOf within original these the historic catchments, terminal the sector amphitheaterthe near two of largest the most Genoa. estuary and important These area. the are:phitheater, and most (1) (2) populous the Bisagno Polcevera basin Stream Stream (140 km (95 which km is 5 5 20 25 15 10 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2458 2457 ) and, particularly, the changes in precipitation 1 − Similarly, historical sources constituted important documents in the reconstruction This study utilizes maps produced after the annexation of the Republic of Genoa to The annual average temperature shows a clear growth according to recent climate The time evolution of the parameters was analyzed using the Standardized Anomaly A number of authors have studied geo-hydrological hazard and its recent increase geological events (Glade et al.,Llasat 2001; et Luino al., et al., 2005;in 2002; Porfido Italy Tropeano et and carried Turconi, al., 2004; outCouncil) 2009). by and Studies Consiglio by about Nazionale Serviziodrographic past and delle geo-hydrological Idrografico Seagraphic events Ricerche e Service) (CNR, Mareograficoet (Cati, al., National 1970; Nazionale 1995) Cipolla Research have (SIMN, been et National used al., to Hy- 1993, gather 1999; the most Tropeano relevant information for the study area. of the areas exposed to the risks due to either the frequency or magnitude of hydro- called map “Gran Cartaand degli produced by Stati Military Sardi Corps.compared di For with all Terraferma” the at maps areas 1 produced analyzed, :IGMI afterwards this 50 (after 000 historic by Italian scale, map the unification, has surveyed 1861): Italianand been in Military 1939 particular were Geographic the used. Institute maps Finallygione of Liguria the 1878, Administration) recent mapped 1907, Regional in 1923,shots 1980, Technical 1934 Cartography 1994 and and (CTR the 2007 by Google obtained Re- opment. by Earth aerial satellite snap- have permitted the comparisons of recent devel- the Kingdom of Savoy (1815). During the period 1815–1830 they it was in use a so- ing trend in the monthlyfloods rainfall occur, amount. it It is is associated noteworthyof with that the a when monthly rainfall important rainfall total autumnal thatin over commonly a opposition falls few to in hours the the greater trendthe autumn than of rainy months. the the In days sum last very number century, recentin and it years, the consequently has year a been it observed decreasethunderstorms. is a in This often slight the seems raining increase related annual with of toon precipitation moderate a the rate: intensity city’s recent gulf but decrease (Anagnostopoulou rarely in et the there al., number are 2006). of very Genoa intense Low year. Analyzing the historical trendrainfall/number (almost of 200 rainy years) days) ofcording it the to precipitation is the rate possible study (annual to byOctober notice Pasquale and a et November, when al. significant flood (1994) increasing events and trend most Russo frequently ac- et occur, showing al. an (2000). increas- The months of variations (Fig. 3). Thetrend total annual for rainfall the shows number acreased of from slight almost rainy decrease. 90 days A per per slight year at negative year the has beginning also of 1800s been to observed. the current They nearly have 80 de- per precipitation, temperature, rainy days and rainfall rate. Index (SAI), which expressesthe the mean anomaly value of ofannual the the basis parameter reference by examined period averaging compared (Coles, the to 2001). standardized The anomalies index for was all calculated parameters on analyzed: floods through many coastal localities.from Climate a factors dataset composed were of studiedversity over by 180 of analyzing years of data Genoa. raingauge The stationand measurements data annual at total were Uni- of used rainyof to days (Cortemiglia, compile daily 2002). the precipitation These annual data rateduring let amount recent (mmdays us years. of analyze precipitation the trend by analyzing meteorological and climateorography of factors Genoa and and their surrounding interactionchini, localities with (Pasquale 1994; the et Russo complex al., et 1994; al.,et Russo 2000; and al., Cevasco Sac- et 2012; al.,the Faccini 2010; atmospheric et Sacchini circulation et generating al., heavy al., 2014). rainfalls 2012; and Meteorological Brandolini more recently factors initiating were flash studied by analyzing pends greatly on historical documents;hydrological the events authors from incorporated both research published on andarea past unpublished reports and geo- pertaining undertook to analysis thewith of local urban historic changes. maps and urban studies to assess interaction 5 5 25 20 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 1 1 − − s 3 ). The 2 − km 1 − s 3 ). 2 − at Castelfidardo bridge, lo- km 1 − 1 s − s 3 3 (12 m 1 − s 3 2460 2459 ). 2 − km 1 − ected Voltri and Genoa before the arrival of the cold front. s ff 3 of water fell in such basin, with a peak of about 160 mm 1 h 1 − and over 500 mm in 6 h. This event struck in particular the Bis- (8.7 m 1 1 − − s ). The flow rate ensured by the Bisagno coverage was approximately 3 2 ected the center of Genoa, in the historic amphitheater, where several − ff . The maximum flow rate of the Polcevera Stream, which barely remained km 1 1 − − s s 3 3 In 1993 on 23 September, with similar weather conditions a new flood event occurred During the severe event occurred on 4 October in 2010, the Mt. Gazzo rain-gauge During the event of 4 November, in 2011, under the same meteorological configu- The 1970 event in Genoa City was also one of the most dramatic. On 7 October, On 27 September 1992, under meteorological circumstances like those of the 1970 agno Valley and themore catchment than 500 of mm 6 Fereggiano h creek, one of its small left tributaries: with values up to 350recorded) mm which in provoked 5 h the near overflowingPegli, of Pegli S. (in Leira Pietro Genoa Stream Stream in over 300 Voltri, incriticalities mm Varenna Genova-Prà of Stream a and rain in tributaries in 15 of h the were Polcevera Stream. Some station (Genoa-Sestri Ponente) measuredthe a cumulative rainfall hourly was peak moreflowed that than and 400 exceeded severely mm 120 damaged over mm the 6small h: and area adjacent the near Cantarena Chiaravagna its Creek Stream mouth flooded over- (Fig. the 1 western catchment part “k”). ofration, Also Sestri the the Ponente town. Vicomorasso rain-gaugenearly station 180 (North mm 1 h Genoa) measured a rainy peak of hood of the Genoa Brignole“mouth”). railway Fortunately, station as and soon theage as district was the called limited. stream Foce Additionally, there (means overflowed,adjacent were steam the Sturla some Creek rain fatalities that stopped near overflowed the a and mouth few dam- hours of before the (Fig. smaller 1, catchment “o”). streams, totally or partiallythe underpass culverted, under overflowed construction withand in the a Piazza current lot Caricamento waterfront ofGenoa). Square drawn damage, The (near by in rainfall the the event particulargauge Old famous regarded stations: Port architect so some Renzo it basins Piano,watercourses. is not who not is provided possible from by to hydrometric comment rain- on the hydrological response of the The creek violently overflowed togetherlassana with area. The other Bisagno small Stream, creeks onof the just the contrary, upstream overflowed artificial upstream the the cover, Mo- beginning floodingof the about center 800 of m Genoa. The peak discharge was estimated within its banks, was estimated at 1656 m 700 m pre-frontal storms struck the westernthe side of day the after. city, The then storms the a center and the hinterland (12 m 4 Genoan geo-hydrological disasters from 1970As to mentioned present earlier, Liguria in generalflood and events Genoa due in to particular the have been predisposingsidering subjected conditions only to of climate Genoa and city, urbansix in morphology. of Con- the them last caused forty-fiveastrous very years, events severe ten resulted damage from important andditions similar events casualties were meteorological took (Table characterized circumstances. 4). place: by The a Five(Bossolasco weather blocking of et anticyclone con- the al., to six 1971; east Cati, and dis- of 1970) a the producing deep perturbation. pre-frontal trough storms to on west the warm branch The heavy rainfall lastedrain-gauge more over than 950 mm 24 h ofBisagno with rainfall in highs Valley, 400 24 in mm h was Polcevera inand Valley. measured. At 24 Over Bisagno h Bolzaneto the stream was city channels recorded. centerdischarge and Cerusa, overflowed gauge the submerging Leira, stations, the Varenna,timated Chiaravagna city the by center. maximum Cati In flow absence (1971), rate of near of the the railway Bisagno station of Stream Genova was Brignole, es- as 950 m event resulted inand rainfall Bisagno for streams 14 h overflowed.Stream The with in maximum a 1992 estimated (Conti cumulated dischargecated et of rainfall just al., the of 1994) upstream Bisagno about was of about 400 the mm. 700 m culverted Sturla stretch near the railway (7.5 m Bisagno overflowed upstream theflooding coverage under the the historic Genoa district Brignole of railway station Borgo Incrociati, the center city around the neighbor- 5 5 20 10 15 25 20 10 15 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − er- ff . In Genoa 1 − s 3 (e.g. Fereggiano 2 ) in time (hours) of the events that have 1 − 2462 2461 , which resulted in a rapid increase in the level erent temporal periods, presumably with di 1 ff − . In the Bisagno and Polcevera basins a rather compli- 2 The high intensity of precipitations of short duration and the sewage system cre- During these severe past events, 400 mm was recorded or exceeded in shorter time Figure 5 shows the trends of hyetograph and hydrograph related to events from 1970 The high intensity within periods of long duration rainfall caused many problems for The most recent disastrous flood event of Genoa occurred on 9–10 October 2014, Other geo-hydrological events occurred in Genoa sinceComparing 1977 the as storm well as events the of most 1970, 1992, 1993, 2010, 2011 and 2014 that hit ated problems especially in the basins with areas lesser than 10 km ent temporal influence on the sub-basins. Creek, and neighboring Noce and Rovarepractically creeks), instantaneous causing flash-flood time phenomena of with response. 5 Genoan urban development Analyzing many maps ofserve the that Republican Genoan Age urban (from developmentnatural 10th was harbor century limited which to to is 1815) thether the we hills inland can actual surrounding were ob- the populated historical only ancient center. bysurrounded Connecting small by villages valleys walls and and for narrow areas military tradechanneled routes fur- defense, streams while was flow the towards open city, the only harborsome to and there the hydrological is sea. problems historical A information (during indicating numberthe the of annexation years small of of the 1222were Republic and built of 1407 triggering Genoa in urbanization tolive of particular). the nowadays. surrounding Since Kingdom valleys where of the Savoy majority (1815) of new citizens roads ized by multiple bursts distributed in di periods. More thanmately 400 mmw.e.re the same recorded value,only in 8 but h 24 h, in in October 15 during h 2011 and October in 2014. September 1970, 1992,to approxi- 2011 up where to we can more observeflood the than (3 h rapid 500 response for mm between Bisagno the in Stream, impulse 4 rainfall h and for the Polcevera Stream). the basins larger thancated 10 response km on the ground of the hydrographic network was observed, character- with a rainfall mechanism linked totioning the for repeated several “self-regenerating” hours thunderstorms, over sta- thethe city, perturbation. which started Between 6.00 up a.m. in onbasin the 9 of warm October pre-frontal the and sector river 12.00 of a.m. Bisagno on were 10 recorded October some on peaks the of rain up to almost 140 mmh and heaps of more than 550 mm 24 h teorological point of view theseflow events in are all the related warm totermined sector, a extremely but block intense action with and and localized theFigure a raining trigger 4 prefrontal able of to shows generate very the flash narrow rainfall floods supercells intensity (Fig. storm 2). (mmh that de- significant in the Genoan metropolitan area are shown inGenoa Table 5. city with extensivesumed flooding that damage rainfall and is casualties becoming in more concentrated the in city, it time (few could hours). be From as- the me- of all streams and subsequentmaximum discharge flooding estimated in by the flood finalcity markers stretch also was of Sturla, more the Fereggiano, than Noce Bisagnoof 800 and stream. West-center m and Torbella The Creeks East-center overflowed: were so inundated. neighborhoods struck Genoa in 1970, 1992,rainfall 1993, peaks 2010, through and 1, 2011Gavette and raingauges). 3, 2014 It 6, and is 12, the possibleof statistics to the 24 h of note Third the Millennium, that directly while rainfallThe in the same intensity the consideration same is can rainfall Bisagno higher be amount in deduceddepth basin was from values the attained (Pontecarrega- the in events in trend the of a station the of shorterValley: annual Pontecarrega, the time. located maximum rainfall in cumulative the rainfall central2014 during sector (an of 1, the exceptional Bisagno 3 eventflood, and with which 6 return was h more period is severe greater (return higher period than in about 200 the years) 50 years) event than over of a the span 2011 1970 of and 12 h. 5 5 15 20 25 10 15 10 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ec- ff in new ff 2464 2463 ered the gradual and complete urbanization of the valley ff tive discharge section (Corominas and2014); Alonso, 1990; Baioni, 2011; Faccini et al., urbanization (Petrucci et al., 2012; Kellens et al., 2013); (Fig. 9), particularly withof the complete the urbanization watercourses ofLuino (Disse the et plain and al., and 2012; Engel, the Luino, 2001; covering 2014); Nirupama and Simonovic, 2007; more restricted areas. The Polcevera Valley (Fig. 8) and particularly its final stretch and the district of Ses- As examples valid for the whole Ligurian context, the urban growths of Genoa- The geo-hydrological problems related to the Genoa urban development can be 3. progradation of the coastal plain towards the4. seatotal with diversion new of embankments the and natural riverbed and concentration of surface runo 1. modifications in land-use changed from predominantly agricultural to urbanized 2. variations in the flood channel width of the streams with narrowing of the e floors; first in thenear middle of the the sea nineteenth wereian century, the when industrial subject such development; strategic of then areasing, the the public located first housing, further facilities industrial extension and settlementsSestri road pursued Ponente infrastructures. that (Fig. with Among 8 allowed the residential westward the Polcevera Polcevera build- occupied Valley stream) Ital- and it by is a possible steelworks to observeabandoned built an and in area demolished. the still 50’s over a large beach area and, now, partially tri Ponente (Fig. 7) have su stretch near Bolzaneto. Thesethen lands they were were autonomous incorporated municipalities inof in the the Genoa the Bisagno municipality past stream) starting and the and from present 1873 in municipality) (end 1926 under stretch the (Polcevera Valley, fascist Sestri dictatorship. Ponente and5.1 the rest of Variations about the land-use The Bisagno basin can be consideredin as land a use. “key-watershed” for Figure thepatterns 6 analysis of of shows change changes could the be areas madefrom on for Voltri all the to the coastal Bisagno Nervi, plains stream and ofstretch the valley also municipality of floors for of all but Bisagno Genoa, the similar Streamthe major coastal is length towns of culverted of the downstream Liguria.of main The parallel which whole watercourse to 0.3 final km in the1.4 totally the km railway culverted of plain (Fig. final just area 10); coverage onbasin is between the the shows about railway flank a 12 and km of relevant thea (24 the mouth. decrease km progressive While Genoa increase of in the of football the total), land-use thethe stadium wooden in urbanized growth and the areas surfaces, of particularly in the near Genoanplans the the population last of mouth occurred two streams: (Fig. when 9); centuries justexamples the at and urban the a pressure Bisagno Mediterranean began level. plain, in unfortunately, the is probably one of the worst grouped into four main geomorphological-environmental issues: Earth for: (1) the endthe stretch Chiaravagna Stream, of (3) the the Bisagno final Stream, stretch (2) of the the town Polcevera of Stream Sestri and Ponente (4) on its valley Bisagno Valley, Genoa-Polcevera Valley and of Genoashown Sestri in Ponente Figs. (2010 6–8. flood) Usingthe are old fluvial maps plain, it which isWorld possible started War to in II. observe the The the building 19th gradualday, numbers while occupation century have the of and increased population from which in 65 the was 000240 area 000 completed in of inhabitants 1861 after the to (1861) the present 305 Genoa to 000urbanization Municipality of to- a rose the maximum from hills about of still continuedof 850 000 in the the in floodplain. 1980s the and 1990s early after 1970s the (Fig. full urbanization 9). The In order to exemplifyfor the location), the anthropic maps changeshave of related been the used to Gran comparing these Carta them four degli with issues Stati the Sardi current (see di state Fig. Terraferma shown 1 (1816–1830) by the maps of Google 5 5 25 20 10 15 20 15 10 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2466 2465 ect, facing upstream. The church was built on the seaside and it is 1 km far from the A new riverbed was excavated and displaced about 300 m towards the west with In Sestri Ponente (Fig. 7) we can observe the Ruscarolo Stream diversion. It does With respect to Sestri Ponente (Fig. 7), around 11th century the sea flew in the Chiar- ff a narrower discharge sectiondoned meander about has been 60 m filled inriverbed less with digging has than debris been of the the used railway original(once tunnels: as an such situation. a autonomous a The filled municipality). preferential aban- settlement for Bolzaneto districtnot flow expansion naturally intothe its urbanized seashore. beach This anymore, was butChiaravagna Stream is accomplished without displaced channel by 400 adjustment m artificially to parallel accommodate diverting to the the new discharge. Ruscarolo into the sea nowadays. These notes showalluvial that plain the since area historical wastors times. interested contributed In by to addition progradation the to of enlargementa this the of natural seashore the trend railway plan. anthropogenic was Inized fac- built the in second the which 20th half facilitated century. of Additionally, the1930’s the the and plane shipyards 19th which the becoming century, were Genoa developed completely airport mainlyin urban- in the “Cristoforo the final Colombo” separation constructed of ining the the town of from 1960’s the the resulted streams. sea Consequently,with by historical cyclopic the floods embankments historical occurred and analysis mainly the identifying in curv-cal events the some at 20th major Sestri century floods Ponente linked inand to 1900, 2010. 1906, strong 1911, meteorologi- 1929, 1945, 1951, 1970, 1977,5.4 1993 The riverbed diversion Urbanization in thissage area of included the railroad riverbed Genoa-Turin(Fig. diversion. (1854) 11). entailed Inland the at cutting of Bolzaneto, a the Polcevera’s meander pas- the 17th century the seae touched the main Church of the “Assunta”, whose portal is, in avagna valley through theof little the San hills. Lorenzo In Gulf 1238 and the a sea little reached harbour lay the at root the of base the present marine terrace, while in dustries. On the leftcontainer bank, harbour, moreover, the the piers and works the related breakwater to dam. the Genoa Sampierdarena In Fig. 8 at theline mouth to of the the Polcevera, sea, we totallytrial can observe due activities. the to It progradation the of is fillingon the possible of the coastal the to banks seaside notice built tostream’s in the create mouth, the total flat built 1990s surfaces banking in and for of indus- the the the commercial 2000’s stream, center in the of place new the of roads Fiumara, abandoned close steel the and engineering in- 5.2 Modifications in the width ofThe riverbed Bisagno riverbed has undergonelast a two significant hundred constriction years.possible in Comparing channel to a width 1830 note in maproad, that the and changed the a approximately St. from recentwas 280 Agata aerial m repeatedly photograph, medieval wide damaged it bridge, to and is theNear built almost actual the along present destroyed 70 m city during the center, (Fig. the thethe ancient 6). so-called beginning floods Roman The Pila of of bridge bridge the crossed 1970 nineteenththe a century and 120 Bisagno is m 1992. stream now wide which constricted channel took at while by at the place the complete in mouth covering the called of 1930s Focecentury) the with to width the an was present actual reduced 50 m. from widthon Similarly about of in the 200 about the (early Via Polcevera 50 Valley, nineteenth the m, Aurelia bridgebeginning of di of Cornigliano, Ponente, the nineteenth passed century over(Fig. but a has 8). been channel reduced of at present about to 150 a m width in5.3 of width 75 m at the The progradation of the coastal line to the sea 5 5 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − ects on the ground ff ects on the ground occur ff in Genoa-Bolzaneto in the Polcevera val- 1 − 2468 2467 ects of global warming, so that the same e ff Consequently, the geo-hydrological risks, determined by the result of hazard and vul- The increased risk posed by the greater frequency of intense rainfall events may be Damages for those flash floods, evaluated starting from the 1953 event just consid- The rainfall amount of the flash floods generated by local supercells are unrivaled In the Liguria central sector, there are special weather-orographic conditions that The increase of precipitation rate with the average temperatures are confirmed by paper, Genoa Cityhydrological and events surrounding over a communities longgraphical have conditions period responsible experienced of for these significant time. events will Theand geo- continue meteorological, may for the climatic, even foreseeable and future become geo- but more can severe. do This little means toban we change development can this potentially risk define at component. the riska Vulnerability continuing hazard from as upward a potential represented spiral future of by disastrousin event the impacts. is New ur- This Orleans, the is Louisiana only similar (USA) means to after the for Hurricane situation avoiding present Katrina where governmental actions nerability, are progressively raised becausehigh of level climatic of change influencingity. hazard The an and resulting existing continuing increaseconsidered urban in an damage development acceptable costs creating level and greater of the risk vulnerabil- number (Nielsen of et deaths al., can 1994). hardly As be documented by this these situations create very high vulnerabilityally, compared the to historic progressive conditions. urbanization Addition- increase of in floodplains population andresults hills, and accompanied in infrastructures by a leading a prominentgreater to marked vulnerability. reduction the also reduction in of the flow times sections, of concentration together with the evaluated not only in terms ofto casualties, the but also floods. in Using termsa of the goods remarkable historical potentially increase exposed maps in of urbanizationeral the in narrowing the last of alluvial two the plains centuriessubsequently watercourses along it artificially flow the is section, riverbeds, diverted, a possible some andthe gen- to examples coastal a note of plain general original due progradation riverbeds to towards human embankments the for seaside further of urbanization. In many places in account that thosetions, events, usually because hit of with their maximum intensity meteorologicaltens only and of a square orographical very kilometers. condi- narrow strip of land involving some ering Genoa city, have beenover increasing 250 from millions 50 euros million of liras the (Tropeano et most al., recent 1993) floods. to These are very high figures taking which pass from 24 h inthere 1970 can to 14 be h more in flash 1992, to floods 5–6 with h continued in the climatic last warming storm (Table events; 5, suggests Fig. 4). in the Mediterranean area: 948 mm 24 h accentuate the e in ever shorter time, asnecessary a to response reach to the the climate same change. precipitation An values evident and reduction the in same time e but not in theof more number recent of climatic rainyLow variations, events days in due particular (Fig. to the the 3b).rainfall, decrease tropical but This air not of change a expansion the decrease towards may number in north, of be the which Genoa rainy a causes days less consequence (Anagnostopoulou annual et al., 2006). ley, north-westward the center nell’at alluvione del Vicomorasso 7–8 raingauge, October 1970, in(Fig. and 13). the 181 mm Genoa 1 h inland nell’alluvione del 4 novembre 2011 data of other worldwidethe recording planet stations (IPCC, which 2013).the demonstrate precipitation The the rate recent global (Fig. 3d) warming slowdown appears of in due to the the growth decrease of in annual an rainfall upward (Fig. 3a), trend in 6 Discussion and conclusion Considering the historical analysising it events appears has that become the intensifiedrence frequency with of has more significant passed recent damag- fromevents times. two between In events 1951–2000, Genoa to per city, four fifty Their events(Fig. years, during recur- 12). the during first the 14 years span of 1800–1950, the to 21st Century six 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | et al., 2015). Fu- ff ort involving both governmental and pri- ff 2470 2469 (Committee on Increasing National Resilience to ects ff ect of more impervious urban surfaces. The intent would be to re- the ability to prepare and plan for, absorb, recover from, and more ff Reducing risk posed by future geo-hydrological events requires both the knowledge management for civil protectionNat. Hazards purposes Earth in Syst. the Sci., 12, urban 943–959, area doi:10.5194/nhess-12-943-2012, of 2012. about Genoa wise (Liguria, governmental NW decisions171–191, Italy), doi:10.1177/0002716205284676, for 2006. hazardous areas, Ann. Am. Acad.Liguria Polit. in S.S., autumn 604, 2011:14, numerical 1325–1340, forecasting doi:10.5194/nhess-14-1325-2014, 2014. experiments, Nat. Hazards Earth Syst.catastrofe Sci., idrogeologica del 19 Junegeomorfologici 1996 e in valutazioni Versilia e idrauliche,Prevenzione Garfagnana delle in: (Toscana, Catastrofi Italia): Atti Idrogeologiche: aspetti il delNovember contributo 1996, Convegno della edited Ricerca Internazionale by: Scientifica, Luino, Alba Alba, F., 5–7 Torino, 96 2, 75–88, – 1998. La Bisagno In Annali Idrologici, parte 2, Istituto Poligrafico dellotriggering Stato, Roma, shallow 74 landslides pp., 1970. onBisagno Valley, the Ital. J. Genoa Engin. Municipality Geol. area Environ., 1, (Italy): 35–50, the 2010. danni case e study sintesi of dei1992, the dati CNR, storici, GNDFI, Roma, in: 1993. Rapporto di evento Savonanazionale 22/9, Genova delle 27 località September dell’informazione, colpite Il rischio daLincei, idrogeologico frane 154 e pp., e 1999. la da difesa inondazioni: del suolo, verso Accademia un Nazionale utilizzo dei 209 più pp., 2001. maturo ence, Engineering, anda Public National Policy, Imperative, National and Academies The Press, 2012. National Academies: Disaster Resilience: 1907. ranean region: present and future climate(HadAM3P), scenarios Adv. Geosci., derived from 7, a 9–14, general doi:10.5194/adgeo-7-9-2006, circulation 2006. model Earth Syst. Sci., 11, 3035–3046,, doi:10.5194/nhess-11-3035-2011 2011. dell’alluvione su Genova del 7–8 ottobre 1970, Geofis. Meteorol., 20, 122–132, 1971. Brandolini, P., Cevasco, A., Firpo, M., Robbiano, A., and Sacchini,Burbey, A.: R. Geo-hydrological J.: risk Hurricane Katrina and the paradoxes of governmentBuzzi, A., disaster Davolio, S., policy: Malguzzi, P.,Drofa, bringing O., and Mastrangelo, D.: Heavy rainfall episodes over Caredio, F., D’Amato Avanzi, G., Puccinelli, A., Trivellini, M., Venutelli, M., and Verani, M.: La Cati, L.: L’evento alluvionale del 7–8 ottobreCevasco, A., 1970 Sacchini, sui A., Robbiano, bacini A., dei and Vincenzi, torrenti E.: Leiro, Evaluation Polcevera of e rainfallCipolla, thresholds F., for Conti, M., Russo, D., and Sebastiani, C.: Mappatura delle aree esondate, sintesi dei Cipolla, F., Guzzetti, F., Lolli, O., Pagliacci, S., Sebastiani, C., andCityRailways: Urbanismi Siccardi, in Italia F.: 2011,Coles, Catalogo available S.: at: , Anwww.cityrailways.net 2011. Introduction to Statistical Modeling of ExtremeCommittee Values, on Springer Verlag, Increasing London, National Resilience to Hazards and Disasters, Committee on Sci- Hazards and Disasters, 2012).adding In to this existing framework, vulnerability futureties and, development provide potentially, could for reduce both replacement it limit and asvulnerability. modification This developmental of is opportuni- urban obviously features avate contributing institutions to long-term who existing e will begeo-hydrologic depending on events the to knowledge properly gained design,City. from Increasing site, the resilience and study will of alter result past urban infrom development decreasing future in vulnerability, geo-hydrological and Genoa events. in turn, reduce risk References Almagià, R.: Studi geografici sopra le frane in Italia,Anagnostopoulou, vol. 3, Chr., Società Tolika, Geografica Italiana, K., Roma, Flocas, H., and Maheras,Baioni, P.: D.: Human Cyclones activity and in damaging landslides and the floods on Mediter- MadeiraBossolasco, Island, Nat. 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C., Barriendos, M., Barrera, A., and Rigo, T.: Floods in Catalonia (NE Spain) since the Luino, F.: Sequence of instability processes triggeredLuino, F.: by A flood heavy can point rainfall out in improper land-use the planning: the northern case Italy, of Alessandria town (Pied- Luino, F., Belloni, A., Padovan, N. in collaboration with Bassi, M., Bossuto, P., and Fassi, P.: Luino, F., Turconi, L., Petrea, C., and Nigrelli, G.: Uncorrected land-useNielsen, planning N. highlighted M., Hartford, D. N. D., and MacDonald, J. J.: Selection of tolerable risk criteria for Conti, M., La Barbera, P., and Lanza, L. G.: Analisi idrologica d’evento: modellazione su base Corominas, J. and Alonso, E. E.: Geomorphological e Cortemiglia, G. C.: Messa a punto di una procedura per l’analisi climatica delle serieCortemiglia, termo- G. 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Hazards, 31, 663–679,tion 2004. with Dutto, F., Godone,e F., 27 Massobrio, settembre R., 1992 and,Quaderni in Beretta, di Liguria. studi E.: Studio e idrologico Gli dialpina, e eventi Torino, documentazione geomorfologico. alluvionali 3–37, n. Supplemento 1993. del 13, a 22 Anno GEAM, XXX, n. 4, Associazione Mineraria Sub- Tropeano, D., Arattano, M., Deganutti, A. M., Luino, F., Ciamartori, L., and Dutto, F.: L’evento Nirupama, N. and Simonovic, S. P.:Pagani, Increase A.: of La Biblioteque flood UniversellePasquale, de risk V., Geneve, Russo, 23 due G., November Sacchini, to 1822. A., urbanisation: and Verdoya, a M.: Precipitation canadian Petrucci, rate O., Pasqua, as A. a A., signal and of Polemio, recent M.: Flash floodPorfido, occurrences S., since Esposito, the E., 17th Alaia, century F., Molisso, in F., and Sacchi, M.: The use of documentary sources Russo, G. and Sacchini, A.: Brief surveyRusso, on G., Eva, recurrences C., of Palau, C., extreme Caneva, rainfalls A., and in Sacchini, Genoa, A.: Italy, The recent increase inSacchini, the A., precipi- Ferraris, F., Faccini, F., andSaéz Firpo, de M.: Càmara, Environmental E., climatic Gangoiti, maps G., of Alonso, Liguria, L., Navazo, M., Gòmez, N., Iza, J.,Silvestro, Garcìa, F., J. Gabellani, S., A., Giannoni, F., Parodi, A., Rebora, N., Rudari, R., and Siccardi,Tropeano, D. F.: and A Turconi, L.: Using historical documents for landslide,Tropeano, D., debris Chiarle, flow M., and Deganutti, stream A., Mortara, G., Moscariello, A., Mercalli, L., in collabora- 5 10 15 20 25 30 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 5) > 6 6 5 6 69 14 14 34 36 12 18 159 Gazzetta Piemontese, 2 Nov 1822; Gazzetta di Genova, 26 Oct 1822; Pagani (1822); Cati (1971) Cati (1971) 15 Oct 1853 Almagià (1907); Tropeano (1993) Cati (1971); Russo and Sacchini (1994); Tropeano et al. (1995) Cati (1971);Sacchini Russo (1994) and Inglese etCati al. (1971);et al. (1995); (1909); Cipolla Tropeano et(1999) al. Cati (1971); Cipolla et(1999); al. Nationalgrafic Service, Hydro- 2/1927 Cati (1971); Cipolla et(1993); al. Russo andchini Sac- (1994);et al. (1995) Tropeano Cati (1971); Cipolla et(1993); al. Russo andchini (1994) Sac- Cati (1971); Cipolla et(1993); al. Russo andchini (1994) Sac- Cipolla et al. (1999) ) 1 at − ) 1 1 − − with 1 . − , 1 1 − − s 3 (Caredio et al., 1 − ) created instability pro- 1 − at Genoa University, in the center city, 1 − DamageMore than 1002000 homeless, urban over 10 areas billiondamage US flooded. in $ all of and railways interrupted Fatalities ( a peak of 157 mm 11998). h Overslopes. 450 Violent flash flood soil hitlages: some slips mud vil- and1500 on homeless debris the up to 4–5 m. of homeless: 358 firms damaged formillions 65 of euro Heavy rainfalls (about 140triggered mm over 72 three h billion tonspyroclastic of such material slidareas. on 1550 homeless, urbanized 200 houses destroyed only on Sarnofor more town. than 500 Damage millions of euro charge increasingcalled of “Fiumara Beltrame”. A awas camping inundated with little victims Some creek days700 mm): of floods rainfallscourses and (more along debris flows on than the mainfans: alluvial severe damage water- to structuresinfrastructures and with victims and 40.000 evacuated Heavy rainfall (52 mm 30 min 145 mm 6 h cesses: many victims intoand cars the houses Intense rainfall andsome streams: four quick people drownedtheir growth in car of 520 mm in less thanincreasing 6 h: of fast discharge manycreeks streams and little 500 mm inof 5 h all provoked watercoursesbuildings flash narrowed and into often floods covered the Intense rainfalla rapid (175,2 mm) increase ofthe the channels: caused large water areas levels inundatedthe in till second floor of the houses at Bolzaneto, 475 mm/48 h 396 mm 24 h at Bolzaneto; Polcevera maximum discharge at Passo dei Giovi but the Polcevera flood re- /s 3 1 1 1 − − − 2476 2475 fall. Flood of manyagno streams: Stream. destroyed two Mudhouses. bridges According and to on sources water the 812 mm Bis- up of cumulated to rainfall. the second floor of the the city: flood of somefloor streams. of Mud the and houses. water up to the second Streams sure is 181.3 mm 24westward h Bisagno Valley. Probably the eventrow involved a area. very nar- measured at Genoa University raingauge (upper Bisagno Valley) in 9est h were concentration recorded, with in high- theagno span estimated discharge 4:00–6:30 was ST about of 420–450 m 18 Jul. Theabout Bis- 1050 m moved the measuringPolcevera discharge was instrument flooded inthe with Lagaccio Bolzaneto. dam. damage The The Bisagno andcover: stream there overflowed deaths. upstream was the Breaking alsoflooded. the of 276 mm/24 Fereggiano hs flood at and Genoa Molassana University was were recorded. Genoa University.creeks Polcevera overflowed at flood; Molassana district. Fereggiano andand Geirato 330 mm inof the Bisagno whole Stream, event floods atland; and damage Molassana at shallow district. railways landslides Flooding and (Genoa-Milan) in at in the the the aqueduct. hinter- Polcevera(more Damage Valley than estimation 25 equal millions to of 50 euro) billion liras towns were inundated. Some bridges were destroyed. process LargeTanaro floods Riversome of and thousand tributaries: ofslides land- on the slopes Flash flood Flood of some torrents: highway, roads Mudflows hit some little towns Debris flowslarge floods and FloodsSoil slips and mudflows hit urbanized areas Flood and overflowing ofFlash some streamssome floods streams of 7 Soil slips and flash floodsmall villagesthe coast involved on banized areas banized areas Hydrological process ?? Floods and landslides.Regular flood Floods and landslides. Overflowings of Gromolo the Creek, Bisagno Vara and and Magra Scrivia StreamsFlash flood Bisagno Streams floods at Molassana and Foce. The only mea- Gazzetta del Almagià Popolo, (1907) Regular flood 206 mm 24 h Regular flood 510 mm 24 h Regular flood 368 mm 24 h Flash flood Intense rainfall: 205 mm/4hs at Genoa University (219 24 h basin and Langhe Hills of Acireale and Gi- arre towns Sarno, Bracigliano, Quindici, Episco- pio, Siano Aosta Valley Savona provinces Sicily/Messina province a marecoli and Piceno;magna/Cervia As- Ro- Cinque Terre Croci/Vara Valley Cinqueterre iera,BisagnoScrivia Valley and then Valley era Valley era Valley, Bis- agno Valley era Valley; Bis- agno Valley Valley, Polcev- era Valley Day(s) Month Year Region/Area5–6 Nov 1994 Geo-Hydrological Piedmont/Tanaro 13 Mar 199519 Jun 1996 Eastern Sicily/Area Tuscany/Versilia Flash flood Intense rainfall: 478 mm 13 h 14 Oct 19965 May 1998 Calabria/Crotone Flash flood Campania/towns of Flood of the Crotone town. Thousands 15–16 Oct 2000 Piedmont and 6 Nov 2000 and 23 Liguria/Imperia and 1 Oct 20093 Mar Eastern 201125 Oct Mare/Sant’Elpidio 2011 Liguria/Spezia- 4 Nov 201112 Nov 201218 Liguria/Genoa Nov 2013 Tuscany/Maremma Flash flood Floods Sardinia/Olbia in ur- Flash flood in ur- Some streams flood urbanized areas 6 9–10 Sep 2000 Calabria/Soverato Flash flood 441 mm of rain caused a rapid dis- Main geo-hydrological events involving Genoa city and neighboring areas from the Day(s) Month Year Area/town26 Oct 1822 Geo- Damage Regular flood 15 h of violent rainfall with more than 760 mm of cumulated rain- Source 1825 Passo13 Oct 1853 Cento 186917 Oct 1872 Sestri Levante Western1878 Lemeglio1885 Riv- 8 Oct 1892 ? Scrivia1905 Genoa, Valley Bisagno Deiva1907 M. Regular flood18 Jul 1908 Floods and landslides ? Floods and landslides in the Scrivia Eastern Valley Riviera Genoa Genoa2 Nov 1926 Regular flood29–30 Floods Oct and 1945 landslides at Floods Genoa, Vobbia Regular Flash and and flood flood Isola landslides Polcev- del Cantone Genoa, Polcev- Bisagno Streams floods at Bisagno Molassana Almagià Streams (1907) and flooded Foce. 246 Foce mm/24 district. hs 238,68–9 mm Nov Almagià at 1951 (1907) Viganego Genoa,19 Sep 1953 Polcev- Almagià (1907) Genoa Bisagno 14 Aug 19631 Nov 1968 Almagià (1907) Genoa Voltri Flash flood Floods and damage at Voltri district Regular flood Violent rainfall and consequent floods: Albisola and Savona Cati (1971) 27 Aug 1842 Genova Flash flood Violent rainfall (247 mm in less than 10 hs) hit the slopes behind Italian severe geo-hydrological processes in the last 20 years. Table 2. 19th century to 1970. Table 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1000 people homeless; 50 000 people 250 people homeless 100 people homeless; Impacts to historic structures and significant construction project ∗ ∗ ∗ 2478 2477 Genoa City) without jobs Impacts from the main geo-hydrological events in Genoa city from 1970. Monthly average rainfall and yearly total in the Genoan area. Original cost in Lira; adjusted to 1970 Euro equivalent. Major Storm Event Date7 Storm-related Oct Deaths 197027 Sep 1992 Damage Losses23 Sep 1993 Other damages 4 Oct 44 2010 fatalities (25 within4 Nov 2011 2 fatalities9–10 in Oct Genoa 2014 City 7 fatalities 1.1 billion Euros 75 million Euros 1 fatality 1 6 fatality fatalities 500 million Euros 90 150 million million Euros 250 Euros million Euros 150 people 20 250 homeless people people homeless homeless ∗ Raingauge StationGenoa UniversitàGenoa Jan Sestri PonenteGenoa Feb Sant’Ilario 106 111 Mar 95 Apr 99 106 144 May 108 104 Jun 85 99 113 Jul 76 Aug 84 95 Sept 53 64 91 Oct 27 37 Nov 60 81 Dec 65 36 TOTAL 99 122 61 153 197 109 111 176 166 124 81 169 1286 136 1073 1284 Table 4. Table 3. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | agno Valley (Dagnino et al., 1978) (more than 50et millions al., of 1993; euros) Tropeano et (Cipolla al., 1993) tims, 5 casualties in thepeano inland et areas al., (Tro- 1993) (Rapallo and S. Margherita Ligure cities) 2005), 1 casuality.overflowed Some in the minor BisagnoValleys torrents and Polcevera 2012) avagna stream and allin Sestri minor Ponente catchments (Sacchini et al., 2011) Vernazza cities (Cinque Terre) Carasco bridge, 2 casualities stream catchment in Bogliasco,ity 1 casual- ) 1 − (mmh ) event 1 − 2480 2479 92 523/2495 Damages for over 100 393/2487 billions of Western liras basins70 (Varenna Valley), 2 211/24 vic- 60 Western basins of Genoa 215/24 (Varenna valley) Boate and93 San 115/3 Siro streams overflowed Lavagna Valley (Faccini et al., 2005) 200/12 Entella stream catchment (Faccini et al., 96 308/5 Teiro Stream catchment87 in Varazze, Chiar- 34 187/3 Entella 176/24 stream58 catchment, collapse of the Eastern52 Genoan basins 162/24 and Entella Poggio stream catchment, 290/12 2 casualities Upper Polcevera valley, 1 casuality 109 405/240 Geirato Stream overflowed, Middle Bis- 146 228/3 Recco stream catchments (Faccini et al., (mm 1 h land (Stura Valley) area and Savona town Western Metropolitan area area ern Genoan Metropoli- tan area area areatown and Varazze area area area area ern Metropolitan area Metropolitan area and inland Main catchments and relative streams crossing Genoa City in the stretch between Year, Month, day(s) Locality1977, 6–8 Oct Genoa city and hinter- Peak Rainfall Notes of the geo-hydrological event 1992, 22 Sep1993, 23–25 Sep Western Metropolitan Genoa center city1994, and 4 Nov2000, Western 6–23 Nov Metropolitan Genoa city and East- 2007, 1 Jun2010, 4 Oct Eastern2011, metropolitan 25 Oct Western metropolitan 2013, 21 Oct Eastern2014, Riviera 18–19 Jan Eastern Eastern Metropolitan 2014, Metropolitan 10–11 Nov 143 Eastern Metropolitan 468/6 Vara Valley catchment, Monterosso and 1995, 5–6 Oct Eastern Metropolitan 2002, 24–26 Nov Genoa city and East- 2014, 15 Nov Genoa city Western Other geo-hydrological processes in Genoa city and main events in Genoa metropoli- Figure 1. the districts of Voltri (W)Pietro; and (f) Nervi S. Michele; (E): (g) (a)(l) S. Vesima; Polcevera; (m) Antonio; (b) Bisagno; (h) Fontanelle; (n) Varenna; (c) Vernazzola; (i)(s) (o) Cerusa; Molinassi; Sturla; S.Pietro; (d) (j) (p) (t) Leira; Cantarena; Priaruggia; Murcarolo; (e) (k) (q)nente S. Chiaravagna; (u) Castagna; and (r) Nervi. the Bagnara; In mouth of theFoce Chiaravagna and boxes Stream, (red the Cornigliano mouth dashed and ofStream lines), the Bisagno near from mouth Bolzaneto. Stream. of W At Polcevera to Stream, theThe E: red center area Sestri of indicates Po- the the city figure, of the Genoa, inset the shows blue area Polcevera indicates the Genoan metropolitan area. Table 5. tan area from 1977. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | annual (d) R² = 0,0206 R² R² = 0,0033 R² y = -0,0027x =-0,0027x y +0,2492 y = 0,0011x =0,0011x y - 0,0998 b) annual rainy days rainy annual b) d) annual rainfall rate rainfall annual d) mean annual temperature, and 1833 1853 1873 1893 1913 1933 1953 1973 1993 2013 1833 1853 1873 1893 1913 1933 1953 1973 1993 2013 3 2 1 0 4 5 4 3 2 1 0 (c) -1 -2 -3 -1 -2 -3

2482 2481 R² = 0,0328 R² y = 0,0034x =0,0034x y - 0,3061 R² = 0,0069 R² y = -0,0016x =-0,0016x y +0,1444 annual rainy days, (b) a) annual rainfall annual a) c) mean air temperature air mean c) Climate trends in Genoa from 1833 to 2014 using the Standardized Anomaly In- Isobars and fronts on the ground during Genoa Low (left). The convergence of cur- 1833 1853 1873 1893 1913 1933 1953 1973 1993 2013 1833 1853 1873 1893 1913 1933 1953 1973 1993 2013 2 1 0 3 5 4 3 2 1 0 6 -1 -2 -3 -1 -2 -3 annual rainfalls,

(a)

precipitation rate. Figure 3. dex: Figure 2. rents coming from northerlypercell and characterized southerly by intense sectors rainfall can able create to the trigger formation ﬂash ﬂoods of (right). a thundery su-

water flow (m3/s) flow water water level (m) level water 900 800 700 600 500 400 300 200 100 0 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 Bolzaneto in 1970, 24 h 24 (a) 12 h 12 2 2006 2010 2014 6 h 6 Sept 1993 Sept 2014 Oct rainfall (Pontecarrega (Pontecarrega rainfallgauge) (Castelfidardoflow water gauge) 3 h 3 rainfall (Fereggiano (Fereggiano rainfallgauge) level (Borgo water Incrociati) 0 80 60 40 20

180 160 140 120 100 0

1 h 1 70 60 50 40 30 20 10 (mm) rainfall rainfall (mm) rainfall

Sept 1992 Sept 2011 Nov

Bisagno in 2011. water level (m) level water water flow (m3/s) flow water 2484 2483 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 (d) 1600 1400 1200 1000 800 600 400 200 0 duration (h) duration Oct 1970 Oct 2010 Oct ) vs. time (hours) for the events occurred on 1970, 1992, 1 − Ponte rain-gauge Carrega Ponte Bisagno in 1992, 1 10 100 1 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 200 10 0 (c)

100

1000 500 450 400 350 300 250 200 150 100 rainfall (mm) rainfall rainfall intensity (mm/h) intensity rainfall rainfall (Bolzaneto (Bolzaneto rainfallgauge) (Polcevera) flowwater rainfall (Gavette (Gavette rainfallgauge) level (Passerella Water gauge) Firpo 0 0

80 60 40 20 80 60 40 20

140 120 100 Rainfall intensity (mmh

rainfall (mm) rainfall 140 120 100 Rainfall vs. water level for the events of 1970, 1992 and 2011: rainfall (mm) rainfall Bisagno in 1970, Figure 5. (b) Figure 4. 1993, 2010, 2011era and 2014 and at BisagnoPontecarrega-Gavette Genoa raingauges valleys), (Bisagno University and Valley, between (Genoa Marassi maximum historical and Molassana). annual center, between rainfall Polcev- depth for 1, 3, 6, 12 and 24 h at Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

2486 2485

Comparison of the ﬁnal stretch of the Chiaravagna Stream 1821 and now. Note the Final stretch of the Bisagno Stream at the beginning of the 19th century (left) and to

urbanization of the plain, shipyardspossible (6), to observe the the little strong harbor(1), progradation and to the the the banks sea, airport the of (7)deviation covering which and that of are has the the entailed Chiaravagna indicated railway. Stream It its by ﬂow3 is into dashed and the orange, 4 Chiaravagna and indicate Stream and the theN.S. not Molinassi dell’Assunta Rio on and in the Ruscarolo the Cantanera beach. Creek historic Streams Numbers at center (2), (dotted of the red), its Sestri beginning number Ponente. of 5 Dashed the is yellow 19th indicates the the century. Church shoreline of Figure 7. present day (right). Note theKennedy complete area urbanization, and the progradation Fiera tobridge del the (1) Mare sea and (4) in of and theleft Pila Piazzale the bridge shoulder narrowing (S. of of Zita) the thedownstream (3). ﬂow bridge the Number section 2 railway rose near shows since the (280Bisagno the m “30”s S. Sant’Agata Stream length). Agata (red Cloister, Note dashed banks where line). thatbeginning the at of In the the 19th orange stream century. beginning dashed is of line completely 1800; we culverted can in see yellow the dashed line the shoreline at the Figure 6. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

) from 1800 to the

cumulative buildings buildings cumulative cumulative

350000 300000 300000 250000 250000 200000 150000 100000 50000 0 inhabitantsx1000 900 800 700 600 500 400 300 200 100 0 after after 2002 2001 1992 to 1992 cumulative 1991 1982 to 1982 wood and and forest wood meadow grass/pasture rock barren population 1981 1972 to 1972

2487 2488 1971 1962 to 1962 1961

1946 to 1946 1945 1919 to 1919 urban area urban olive shrubbery vineyard cultivation special buildings for year construction 1919 before before 0 1800 1850 1900 1950 2000 0

80 70 60 50 40 30 20 10 80000 70000 60000 50000 40000 30000 20000 10000 90000 80000 70000

values % values 100000

buildings in Genoa in buildings buildings in Genoa in buildings Final stretch of the Polcevera Stream: 1821 (left) and now (right). It is possible to

Land-use trend in the Bisagno Stream basin (area of about 93 km Figure 9. present day, and Genoa’s population(above); proceeding number since of buildings the in birth2001 Genoa of (below). from the the Italian end Republic of the to First date World War to date, from ISTAT, Figure 8. note the change innarrowing land-use of on the the CorniglianoSampierdarena coast, bridge harbour its (4), (1), strong the the narrowing barrierthe of urbanization in sea. the the of sea It useful the (3) ﬂowreduced is plain, and section, to the also the impressive a the steelworks important progradation channel. towards (2),ginning to Orange of the dashed observe the indicates 19th that century; the the yellow slope dotted water of marks the course the Polcevera shoreline with Stream in braided at the the facies same period. be- has been Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

1 1 2490 2489

The Bisagno stream culvert during its construction (1930) and nowadays. Bolzaneto urban area in the medium stretch of Polcevera Stream: (left) at the begin-

Figure 11. ning of the 19thtill century, the (right) half today. of With 19ththe number century Genoa–Turin 1 the railway church was is was realized evidenced locatedembanked, (black the on line) removing San the the its right Polcevera Francesco riverbed bank, Friary: bend.Murta was inside straightened A Hill: a and large so new bend. the riverbed When narrowing San of was Francesco the digged Friary useful moved for sectionin from 500 of the m, the the present right cutting ﬂowstream, aerial to which thethe banks the photograph. populated foot are left The center indicate of bank. of largest with Bolzaneto. the It part orange is dotted of evident the the abandoned meander is occupied by Figure 10. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

erent ﬂood events. ﬀ October 2010: Chiar- (c)

1 1

2492 2491 November 2011: Genova Brignole railway station (d) Main flood events in Genoa events flood Main ). September 1992: the swollen waters of the Bisagno have destroyed a (b) 1801-1850 1851-1900 1901-1950 1951-2000 2001-2014 7 6 5 4 3 2 1 0

Inundations in Genoa city: some dramatic photographs of di Semicentennial distribution of the most important ﬂood events in Genoa city since n. of events/50 years events/50 of n.

October 1970: Bisagno overﬂowing in the zone downstream the covering near the Genova Figure 13. Brignole railway station; (a) some arches of theavagna’s inundation Sant’Agata in bridge, Sestri already Ponente; damaged in 1970; inundated again (compare Figure 12. 1801. In the present Millennium four events have been occurred in only 14 years.