Climate Change Effects on Hydropower Potential in the Alcantara River Basin in Sicily (Italy)

Abstract In recent years, increasing attention has been paid to hydropower generation, since it is a renewable, efficient, and reliable source of energy, as well as an effective tool to reduce the atmospheric concentrations of greenhouse gases resulting from human activities. At the same time, however, hydropower is among the most vulnerable industries to global warming, because water resources are closely linked to climate changes. Indeed, the effects of climate change on water availability are expected to affect hydropower generation with special reference to southern countries, which are supposed to face dryer conditions in the next decades. The aim of this paper is to qualitatively assess the impact of future climate change on the hydrological regime of the Alcantara River basin, eastern Sicily (Italy), based on Monte Carlo simulations. Synthetic series of daily rainfall and temperature are generated, based on observed data, through a first-order Markov chain and an autoregressive moving average (ARMA) model, respectively, for the current scenario and two future scenarios at 2025. In particular, relative changes in the monthly mean and standard deviation values of daily rainfall and temperature at 2025, predicted by the Hadley Centre Coupled Model, version 3 (HadCM3) for A2 and B2 greenhouse gas emissions scenarios, are adopted to generate future values of precipitation and temperature. Synthetic series for the two climatic scenarios are then introduced as input into the Identification of Unit Hydrographs and Component Flows from Rainfall, Evapotranspiration and Streamflow Data (IHACRES) model to simulate the hydrological response of the basin. The effects of climate change are investigated by analyzing potential modification of the resulting flow duration curves and utilization curves, which allow a site's energy potential for the design of run-of-river hydropower plants to be estimated

Combining regional rainfall frequency analysis and rainfall-runoff modelling to derive frequency distributions of peak flows in ungauged basins: a proposal for Sicily region (Italy)

Abstract. In the present study an attempt is made to provide a general Monte Carlo approach for deriving flood frequency curves in ungauged basins in Sicily region (Italy). The proposed procedure consists of (i) a regional frequency analysis of extreme rainfall series, combined with Huff curves-based synthetic hyetographs, for design storms and (ii) a rainfall-runoff model, based on the Time-Area technique, to generate synthetic hydrographs. Validation of the procedure is carried out on four gauged river basins in Sicily region (Italy), where synthetic peak flow frequency curves, obtained by simulating 1000 flood events, are compared with observed values. Results of the application reveal that the proposed Monte Carlo approach is suitable to reproduce with reasonable accuracy the hydrologic response of the investigated basins. Given its relative simplicity, the developed procedure can be easily extended to poorly gauged or ungauged basins

Influence of storm drain inlet locations on urban pluvial flooding hazard at local scale

The assessment of the impact of surface drainage conditions and the related effect on urban flooding is the general aim of the present research study. Aim of the work presented here is to assess the impact of surface drainage conditions and the related effect on urban flooding. The main objective is to analyze the surface drainage efficiency by evaluating the influence of storm drain inlet location on pluvial flooding. In this study the FLURB-2D propagation model has been used, a two-dimensional inertial model based on the Saint Venant equations and it was, originally, developed with a different purpose. This study focuses on the impact of surface drainage system, in terms of positioning, number, on pluvial flood hazard, actually, four different hypothetical scenarios for the location of the drain inlets were considered. The methodological approach presented in this study is applied in a real case study in the town of Messina (Italy) The area is, entirely, densely urbanized, with streets and blocks with limited pervious parts. The drainage system is mainly separated from the sewer system and there is no stormwater drainage system

Flood and landslide warning based on rainfall thresholds and soil moisture indexes: the HEWS (Hydrohazards Early Warning System) for Sicily

Abstract. The main focus of the paper is to present a flood and landslide early warning system, named HEWS (Hydrohazards Early Warning System), specifically developed for the Civil Protection Department of Sicily, based on the combined use of rainfall thresholds, soil moisture modelling and quantitative precipitation forecast (QPF). The warning system is referred to 9 different Alert Zones in which Sicily has been divided into and based on a threshold system of three different increasing critical levels: ordinary, moderate and high. In this system, for early flood warning, a Soil Moisture Accounting (SMA) model provides daily soil moisture conditions, which allow to select a specific set of three rainfall thresholds, one for each critical level considered, to be used for issue the alert bulletin. Wetness indexes, representative of the soil moisture conditions of a catchment, are calculated using a simple, spatially-lumped rainfall–streamflow model, based on the SCS-CN method, and on the unit hydrograph approach, that require daily observed and/or predicted rainfall, and temperature data as input. For the calibration of this model daily continuous time series of rainfall, streamflow and air temperature data are used. An event based lumped rainfall–runoff model has been, instead, used for the derivation of the rainfall thresholds for each catchment in Sicily characterised by an area larger than 50 km2. In particular, a Kinematic Instantaneous Unit Hydrograph based lumped rainfall–runoff model with the SCS-CN routine for net rainfall was developed for this purpose. For rainfall-induced shallow landslide warning, empirical rainfall thresholds provided by Gariano et al. (2015) have been included in the system. They were derived on an empirical basis starting from a catalogue of 265 shallow landslides in Sicily in the period 2002–2012. Finally, Delft-FEWS operational forecasting platform has been applied to link input data, SMA model and rainfall threshold models to produce warning on a daily basis for the entire region

Human-flood interactions in Rome over the past 150 years

Abstract. Throughout history, the socio-economic development of the city of Rome has been intertwined with the magnitude and frequency of flooding events from the Tiber, one of Italy's largest rivers. Ancient Rome mostly developed on the hills, while the Tiber's floodplain was mainly exploited for agricultural purposes. A few small communities did settle in the riparian areas of the Tiber, but they had a relatively peaceful relationship with the frequent occurrence of flooding events. Instead, numerous people live nowadays in modern districts in the Tiber's floodplain, unaware of their exposure to potentially catastrophic flooding. This research work aims to explore the dynamics of changing flood risk between these two opposite pictures of ancient and contemporary Rome. To this end, we carried out a socio-hydrological study by using long time series of hydrological (extreme flood events) and social (human population dynamics) processes, along with information about human interactions with the environment (flood defence structures). The historical analysis showed how human and water systems have been co-evolving over time, while being abruptly altered by the occurrence of an extreme flood event in 1870, just before Rome became the capital of a recently unified Italy. The outcomes of this study were then compared to the results of a socio-hydrological model simulating the dynamics emerging from the mutual shaping of floods and societies

Megafloods in Europe can be anticipated from observations in hydrologically similar catchments

Megafloods that far exceed previously observed records often take citizens and experts by surprise, resulting in extremely severe damage and loss of life. Existing methods based on local and regional information rarely go beyond national borders and cannot predict these floods well because of limited data on megafloods, and because flood generation processes of extremes differ from those of smaller, more frequently observed events. Here we analyse river discharge observations from over 8,000 gauging stations across Europe and show that recent megafloods could have been anticipated from those previously observed in other places in Europe. Almost all observed megafloods (95.5%) fall within the envelope values estimated from previous floods in other similar places on the continent, implying that local surprises are not surprising at the continental scale. This holds also for older events, indicating that megafloods have not changed much in time relative to their spatial variability. The underlying concept of the study is that catchments with similar flood generation processes produce similar outliers. It is thus essential to transcend national boundaries and learn from other places across the continent to avoid surprises and save lives

Rainfall thresholds derivation for warning pluvial flooding risk in urbanised areas

Aim of this work is the development of an operational tool for pluvial flooding warning in an urban area based on off-line rainfall thresholds derived by coupling a rainfall–runoff modelling and a hydraulic routing. The critical conditions considered for issue flood warnings were not only based on the water stage, but also on the extension of the flooded area. Further, a risk assessment framework for quantifying the reliability of the rainfall thresholds has been included; rainfall thresholds used in pluvial flooding warning should be influenced by the uncertainties in the rainfall characteristics (i.e. rainfall duration, depth and storm pattern). This risk assessment framework incorporates the correlated multivariate Monte Carlo simulation method, an hydraulic model for the simulation of rainfall excess propagation over surface urban drainage structures, i.e. streets and pathways. Thresholds rainfall are defined using a number of inundation criteria, to analyze the change in the rainfall threshold due to various definitions of inundation. Starting from estimated water stages and flooded area from inundation simulation rainfall thresholds can be obtained according a specific inundation criterion, including, together, a critical water depth and a critical flooding area. Finally, the second phase concerns the imminence of a possible hydrological risk by comparing the time when cumulative rainfall and rainfall thresholds meet to each other. The developed procedure has been applied to the real case study of Mondello catchment in Palermo (Italy)

Effectiveness and applicability of flood barriers for risk mitigation in flash-flood prone Mediterranean area

The new policy of flood risk management is to give more attention to non-structural measures, allowing people to “live with floods” rather than “fight floods”. To protect existing buildings there are two main mitigation strategies: dry proofing and wet proofing. One measure of dry proofing is the shielding, consisting in the use of flood barriers, which can be installed at the entrance of the buildings or at a certain distance from them (including the placing along the banks or crossing a street). These flood protection structures are easier and faster to install rather than sandbags. This paper shows the results applied to a case study in the city of Barcellona, Sicily, Italy that is crossed by a river and suffered a severe inundation in November 2011. To study the effectiveness of using these flood barriers, a 2D hydrodynamic model has been used: the barriers has been placed along a road to inhibit the flow from flooding the protected area. While in North Europe these types of barriers are commonly used, because those areas are typically interested in clear water floods, in Italy flash floods and mud-debris-flows are more frequent and limit their use. The purpose of this work is to verify if these types of barriers are effective when placed along Mediterranean river courses and, especially, to be sure about their stability while subjected to the hydrodynamic effects of these kind of events. To gain this aim, the computed stresses from the modelling have been compared with the stability values of the barriers provided by the producers, evaluating barriers’ stability against overturning and sliding. Simulations show how the flood barriers can mitigate the hydraulic risk, being able to withstand the hydrodynamic pressures and managing to divert the flow of water, thus avoiding that the flood water hits very exposed areas

Efficienza idrologico-idraulica di pavimentazioni semi-permeabili per il controllo degli allagamenti pluviali

La sostenibilità del binomio “acqua – città” è uno spunto interessante di discussione e confronto nell’ambito delle diverse discipline che affrontano il tema dell’ambiente urbano, delle sue continue trasformazioni, e della necessità di resilienza agli allagamenti. Le soluzioni tecniche e tecnologiche oggi a disposizione di chi si occupa di queste problematiche, per affrontare il tema di un rapporto sostenibile tra l’acqua e l’ambiente urbano sono molteplici, alcune tradizionali e di consolidata esperienza, altre innovative e di più recente applicazione sul campo. L’urbanizzazione influisce negativamente sulla formazione e propagazione dei deflussi; nelle aree urbanizzate i rapidi processi di trasformazione che hanno caratterizzato gli ultimi decenni, hanno avuto come conseguenza la crescita del grado di impermeabilizzazione dei bacini e, naturalmente, l’aumento dei deflussi e dei volumi generati in tempo di pioggia. Pratiche alternative ai classici interventi strutturali di mitigazione delle piene, sono i sistemi di drenaggio urbano sostenibile, noti anche come Low Impact Development (LID), o Best Management Practices (BMP), o Sustainable Urban Drainage Systems (SUDS). Il loro compito principale è quello di controllare le acque bianche tramite l’utilizzo tecnologie a basso impatto ambientale, che sfruttino e valorizzino le risorse naturali e che puntino al mantenimento del regime idrico presente prima dell’urbanizzazione. Nell’ambito di questo studio sono state prese in considerazione pavimentazioni permeabili che permettono l’infiltrazione di acqua piovana nei vari strati del suolo con riduzione, anche significativa, di eventuali allagamenti superficiali. Come caso di studio è stata considerata l’area di pertinenza, adibita a parcheggio, del centro commerciale Forum di Palermo, complesso architettonico ad uso commerciale situato tra il quartiere residenziale Roccella e la zona industriale di Brancaccio, la cui costruzione è avvenuta tra il 2008 e il 2010. In particolare, lo studio ha previsto l’utilizzo del modello idrodinamico FLURB-2D per simulare la propagazione bidimensionale di inondazione nell’area di studio [1; 2] nella sua versione aggiornata al fine di includere nella propagazione del moto bidimensionale il comportamento idraulico delle caditoie. La schematizzazione ‘fisicamente basata’ delle caratteristiche geometriche del dominio di calcolo permette di considerare come ingresso al modello una forzante pluviometrica distribuita e temporalmente variata. Inoltre, è stato utilizzato un codice mono-dimensionale, basato sul modello Green & Ampt [3] implementato all’interno del FLURB-2D, per verificare l'efficacia delle pavimentazioni permeabili utilizzate. L’impatto della precipitazione sull’efficienza del drenaggio superficiale è stata analizzata confrontando i tiranti idrici massimi e l’estensione dell’area allagata che si sono osservate per diverse condizioni di precipitazione e con riferimento a diversi scenari di simulazione. I risultati ottenuti, mettono in evidenza l’influenza delle diverse configurazioni di pavimentazioni permeabili adottate rispetto allo stato attuale sulla capacità di drenaggio della rete superficiale