Probabilistic floodplain hazard mapping: managing uncertainty by using a bivariate approach for flood frequency analysis

Floods are a global problem and are considered the most frequent natural disaster world-wide. Many studies show that the severity and frequency of floods have increased in recent years and underline the difficulty to separate the effects of natural climatic changes and human influences as land management practices, urbanization etc. Flood risk analysis and assessment is required to provide information on current or future flood hazard and risks in order to accomplish flood risk mitigation, to propose, evaluate and select measures to reduce it. Both components of risk can be mapped individually and are affected by multiple uncertainties as well as the joint estimate of flood risk. Major sources of uncertainty include statistical analysis of extremes events, definition of hydrological input, channel and floodplain topography representation, the choice of effective hydraulic roughness coefficients. The classical procedure to estimate flood discharge for a chosen probability of exceedance is to deal with a rainfallrunoff model associating to risk the same return period of original rainfall, in accordance with the iso-frequency criterion. Alternatively, a flood frequency analysis to a given record of discharge data is applied, but again the same probability is associated to flood discharges and respective risk. Moreover, since flood peaks and corresponding flood volumes are variables of the same phenomenon, they should be, directly, correlated and, consequently, multivariate statistical analyses must be applied. This study presents an innovative approach to obtain flood hazard maps where hydrological input (synthetic flood design event) to a 2D hydraulic model has been defined by generating flood peak discharges and volumes from: a) a classical univariate approach, b) a bivariate statistical analysis, through the use of copulas. The univariate approach considers flood hydrographs generation by an indirect approach (rainfall-runoff transformation using input rainfall hydrographs derived from IDF curves) and a direct approach (statistical inference on measured flood peaks). In the bivariate approach synthetic hydrographs were generated by means two different approaches: an indirect one, where rainfall were generated by a stochastic bivariate rainfall generator to be entered a distributed conceptual rainfall-runoff model that consisted of a soil moisture routine and a flow routing routine; and a direct one, where stochastic generation of flood peaks and flow volumes have been obtained via copulas, which are capable to describe and model the correlation between these two variables. Finally, to highlight the advantages of the presented approach, probabilistic flood hazard maps (including uncertainty) derived by bivariate models are compared to maps from univariate analysis. The procedure is applied to a real case study located in the southern part of Sicily, Italy, where flood hazard and risk maps have been obtained and compared

Effects of Forest Fires on Flood Frequency Curves in a Mediterranean Catchment/Effets d'incendies de for�t sur les courbes de fr�quence de crue dans un bassin versant M�diterran�en

The effect of land-use change on the flood frequency curve (FFC) in a natural catchment is analysed. To achieve this, a simple methodology for the derivation of FFCs in land-use change scenarios is proposed. The adopted methodology, using a stochastic model in Monte Carlo simulation of FFCs, was found to provide a useful framework for detecting changes in flood magnitudes in both pre- and post-fire conditions. In particular, the importance of the antecedent soil moisture condition in the determination of the flood frequency distribution was analysed. The analysis of FFCs for pre- and post-fire conditions shows an increase in the average value of Curve Number and a decrease in the catchment time lag. The derivation of FFCs shows a clear increase in flood quantiles. For the post-fire conditions, the FFC exhibits higher quantiles of the peak discharges showing a reduction in frequency of occurrence. This variation is more significant for low-return period quantiles than for high-return period quantiles. The results of the catchment studies reported here support the hypothesis that the hydrological response of the watershed changes as a result of fire, especially during the first years following a fire event

Natural killer cells modulate motor neuron-immune cell cross talk in models of Amyotrophic Lateral Sclerosis.

In amyotrophic lateral sclerosis (ALS), immune cells and glia contribute to motor neuron (MN) degeneration. We report the presence of NK cells in post-mortem ALS motor cortex and spinal cord tissues, and the expression of NKG2D ligands on MNs. Using a mouse model of familial-ALS, hSOD1G93A, we demonstrate NK cell accumulation in the motor cortex and spinal cord, with an early CCL2-dependent peak. NK cell depletion reduces the pace of MN degeneration, delays motor impairment and increases survival. This is confirmed in another ALS mouse model, TDP43A315T. NK cells are neurotoxic to hSOD1G93A MNs which express NKG2D ligands, while IFNγ produced by NK cells instructs microglia toward an inflammatory phenotype, and impairs FOXP3+/Treg cell infiltration in the spinal cord of hSOD1G93A mice. Together, these data suggest a role of NK cells in determining the onset and progression of MN degeneration in ALS, and in modulating Treg recruitment and microglia phenotype

Derivation of flood frequency curves in poorly gauged Mediterranean catchments using a simple stochastic hydrological rainfall-runoff model

In this paper a Monte Carlo procedure for deriving frequency distributions of peak flows using a semi-distributed stochastic rainfall-runoff model is presented. The rainfall-runoff model here used is very simple one, with a limited number of parameters and practically does not require any calibration, resulting in a robust tool for those catchments which are partially or poorly gauged.The procedure is based on three modules: a stochastic rainfall generator module, a hydrologic loss module and a flood routing module. In the rainfall generator module the rainfall storm, i.e. the maximum rainfall depth for a fixed duration, is assumed to follow the two components extreme value (TCEV) distribution whose parameters have been estimated at regional scale for Sicily. The catchment response has been modelled by using the Soil Conservation Service-Curve Number (SCS-CN) method, in a semi-distributed form, for the transformation of total rainfall to effective rainfall and simple form of IUH for the flood routing. Here, SCS-CN method is implemented in probabilistic form with respect to prior-to-storm conditions, allowing to relax the classical iso-frequency assumption between rainfall and peak flow. The procedure is tested on six practical case studies where synthetic FFC (flood frequency curve) were obtained starting from model variables distributions by simulating 5000 flood events combining 5000 values of total rainfall depth for the storm duration and AMC (antecedent moisture conditions) conditions. The application of this procedure showed how Monte Carlo simulation technique can reproduce the observed flood frequency curves with reasonable accuracy over a wide range of return periods using a simple and parsimonious approach, limited data input and without any calibration of the rainfall-runoff model

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)

Analisi di un sistema di raffrescamento passivo integrativo a sistemi tradizionali per una torre residenziale, Palermo

Analisi di un sistema di raffrescamento passivo integrativo a sistemi tradizionali per una torre residenziale, Palerm

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