Reconstruction of a Storm Map and New Approach in the Definition Of
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water Article Reconstruction of a Storm Map and New Approach in the Definition of Categories of the Extreme Rainfall, Northeastern Sicily Francesco Fiorillo 1,*, Nazzareno Diodato 2 and Massimiliano Meo 3 1 Dipartimento di Scienze e Tecnologie, Università degli Studi del Sannio, via dei Mulini 59/A, Benevento 82100, Italy 2 Met European Research Observatory, HyMex Mediterranean Experiment Network—Via Monte Pino, Benevento 82100, Italy; [email protected] 3 CMG Testing S.r.l., Via Piano Alvanella, Monteforte Irpino, Avellino 83024, Italy; [email protected] * Correspondence: francesco.fi[email protected]; Tel.: +39-0824-305-195 Academic Editor: Brigitte Helmreich Received: 16 June 2016; Accepted: 21 July 2016; Published: 5 August 2016 Abstract: After more than 350 mm of rainfall fell in a few hours on 22 November 2011, thousands of landslides and floods were induced in two main zones of Northeastern Sicily. The total rainfall has been reconstructed integrating available rain gauge data with Tropical Rainfall Measuring Mission (TRMM) satellite data from NASA (National Aeronautics and Space Administration); the landslide distribution in the field has confirmed the pattern of rainfall accumulated on 22 November 2011. Precipitation maxima of 1, 3, 6, 12, and 24 h was recognized as the hazardous events, which marks the evidence of a changing climate, with a shift toward more intense rainfalls in recent times. To investigate the sequence of the annual maxima, the historical time series have been transformed in the Standard normal distribution, from the cumulative probability of the GEV (Generalized Extreme Value) distribution. Following a similar definition of the Standard Precipitation Index (SPI), the transformation of the historical data in the standardized values allows the definition of categories of hourly maxima in term of extreme, severe, moderate, or mild. This transformation allows to eliminate the asymmetry of the time series, so that trends and fluctuations have been highlighted by the progressive accumulation of data (Rescaled Adjust Partial Sum). This statistical approach allows the improvement of the interpretability of the hydrological extreme events, and could also be used in other cases. Keywords: rainfall; extreme event; return time; Standard normal distribution; Sicily 1. Introduction Despite hydroclimate millennia reconstruction not supporting a general unprecedented intensification of the Northern Hemisphere hydrological cycle in the twentieth century associated with both more extreme wet and dry conditions [1], rainstorms and their injuries are becoming more dangerous as population and infrastructure continue to increase and to occupy areas exposed to flood risk [2,3]. However, few literature sources are available worldwide regarding extreme precipitation and, especially, about rainstorm effects on regional and subregional terrestrial ecosystems and water resources [4–7]. This also poses another question related to the development of dynamic hydrological models, hampered by incomplete understanding of spatially-varying processes and the lack of adequate datasets to spatially characterize varying rain inputs. According to [8], secular and more records of historical precipitation data are required to deal with long-term studies and cross-site comparisons. This is especially so in the Mediterranean region, where human pressure and erratic Water 2016, 8, 330; doi:10.3390/w8080330 www.mdpi.com/journal/water Water 2016, 8, 330 2 of 15 Water 2016, 8, 330 2 of 15 rainstorm patterns with marked inter-annualinter‐annual variability expose landforms to exacerbated, damaging hydrological processes [[9–12].9–12]. This is also so to spur thethe emergence of new hazards, suchsuch as coastalcoastal and urban floodingflooding [[13,14].13,14]. Mediterranean rainstorms and cyclones tendtend toto be characterized by short lifelife cycles,cycles, with with average average radii radii ranging ranging from from 300 to 300 500 kmto 500 (after km [15 (after]), many [15]), of which many are of a which combination are a ofcombination both frontal of and both convective frontal storms.and convective Heavy flooding storms. and Heavy storms flooding occurring and at storms Mediterranean occurring sites at wereMediterranean found to be sites characterized were found by to abe complex characterized property, by a known complex as property, multifractality, known which as multifractality, is the spatial distributionwhich is the organized spatial distribution into clusters organized of high-rainfall into clusters localized of high cells‐rainfall embedded localized within cells a larger embedded cloud systemwithin a or larger clusters cloud of lower system intensity or clusters [16]. of lower intensity [16]. Sicily has been hit recentlyrecently byby intenseintense rainstorms,rainstorms, which caused floodsfloods and landslides in many places.places. Particularly affected by recent and intense storms has been the northwestern sector, where a high andand continuous continuous ridge, ridge, the the Peloritani Peloritani Mountains, Mountains, extends extends between between the the Ionian Ionian and and Tyrrhenian Tyrrhenian seas. Duringseas. During recent recent years, years, the most the most catastrophic catastrophic event event occurred occurred on 1 Octoberon 1 October 2009 along2009 along the Ionian the Ionian side, withside, morewith thanmore 200 than mm 200 recorded mm recorded in a few in hours, a few and hours, hit the and village hit the of Giampilieri,village of Giampilieri, where landslides where causedlandslides 36 deaths caused [17 36,18 deaths]. After [17,18]. 13 November After 1855,13 November the event of1855, 2009 the was event the most of 2009 catastrophic was the to most have occurredcatastrophic in the to Messinahave occurred province, in the and Messina follows province, other catastrophic and follows events other that catastrophic have occurred events recently. that Inhave particular, occurred on recently. 25 October In 2007 particular, an intense on rainstorm25 October induced 2007 an many intense landslides rainstorm and floods induced along many the Ionianlandslides coast and [19 floods,20]. along the Ionian coast [19,20]. The stormstorm of of 22 22 November November 2011 2011 hit a hit wide a areawide the area Tyrrhenian the Tyrrhenian sector of thesector Peloritani of the mountains, Peloritani andmountains, caused and three caused deaths three in Saponara deaths in village Saponara (Figure village1). It (Figure induces 1). thousands It induces of thousands shallow landslides of shallow inlandslides two distinct, in two wide distinct, areas wide (Figure areas2), (Figure one located 2), one in located the middle in the catchment middle catchment of the Saponara of the Saponara torrent, andtorrent, the otherand the across other both across the catchments both the catchments of Mela and of Longano Mela and torrents. Longano Huge torrents. alluvial Huge phenomena alluvial occurredphenomena in theoccurred urban in area the ofurban Barcellona area of PozzoBarcellona di Gotto Pozzo and di Milazzo.Gotto and Recent Milazzo. landslides Recent landslides and flash floodsand flash hit floods the same hit area the same on 11 area December on 11 December 2008, 2 November 2008, 2 November 2010, and 102010, October and 10 2015. October 2015. Figure 1.1. (A) The mouth of Longano River on thethe morning of 2323 NovemberNovember 2011,2011, andand thethe bridgebridge collapsed after the the flood; flood; ( (BB)) tree tree trunks trunks obstruct obstruct the the river river flow flow in in town town center center of of Barcellona Barcellona Pozzo Pozzo di diGotto; Gotto; (C ()C debris) debris flows flows hit hit Varela Varela village, village, Mela Mela river river catchment; catchment; and and ( (DD)) a a debris avalanche struck houses in Scarcelli village,village, SaponaraSaponara municipality,municipality, and and caused caused three three deaths. deaths. Water 2016, 8, 330 3 of 15 Water 2016, 8, 330 3 of 15 Figure 2. The northeastern sector of Sicily, characterizedcharacterized by the PeloritaniPeloritani ridge, extended between the Tyrrhenian andand IonianIonian sea; (1) rain gauge network working and rainfall recorded on 22 November 2011; (2) catchment boundary of the Peloritani ridge, Tyrrhenian side; (3) catchment of Longano (A), (A), Idria (B), Mela (C) and Saponara (D) torrent affected by floodsfloods on 22 November 2011; and (4) the area hit by landslides onon 2222 November November 2011. 2011. Damage Damage occurred occurred mainly mainly in in the the villages villages of of Barcellona Barcellona Pozzo Pozzo di Gottodi Gotto and and Saponara, Saponara, which which are are highlighted highlighted by by the the white white circles. circles. In this study we estimate the rainfall that fell on 22 November 2011 by the rain gauge data available, integrated with satellite data; the time of the landslide occurrences has helped in an attempt to definedefine the main features of thethe storm.storm. The historical time series of the annual maxima of rainfall, for different time duration, have been analyzed to estimate the frequency of extreme rainfall events events and and to to highlight highlight trend trend and and fluctuations. fluctuations. 2. Materials Materials and and Methods Methods 2.1. Main Physical and Geomorphological Characteristics of the Area Hit by the Storm Due toto its its climate, climate, affected affected by long, by drylong, periods dry followedperiods byfollowed heavy rainstorms, by heavy the rainstorms, Mediterranean