Coastal zone water quality: Calibration of a water-turbidity equation for MODIS data

A nephelometric turbidity algorithm has been specifically calibrated for coastal waters in Sicily. To this purpose, intensive field campaigns were performed in July, August and September 2008. Measurements were collected in situ in three different gulfs. Statistical analysis suggests that field data should be spatially grouped but temporally separated; hence, new calibration parameters have been proposed. Turbidity retrieved by applying the algorithm using literature coefficients and the ones calibrated in situ are shown and compared. The comparison demonstrated that a specific calibration was necessary for quantitatively monitoring turbidity in Sicilian gulfs

The classification of submerged vegetation using hyperspectral MIVIS data

The aim of this research is to use hyperspectral MIVIS data to map the Posidonia oceanica prairies in a coastal lagoon (Stagnone di Marsala). It is approximately 12 km long and 2 km wide and is linked to the open sea by two shallow openings. This environment is characterised by prairies of phanerogams, the most common of which is Posidonia oceanica, an ideal habitat for numerous species of fish, molluscs and crustaceans. A knowledge of the distribution of submerged vegetation is useful to monitor the health of the lagoon. In order to classify the MIVIS imagery, the attenuation effects of the water column have been removed from the signal using Lyzenga’s technique. A comparison between classifications using indices obtained using band pairs from only the first spectrometer, and using band pairs of the first and second spectrometers, shows that the best classification is obtained from some indices derived from the first spectrometer. Field controls carried out in July 2002 were used to determine the training sites for the supervised classification. Twelve classes of bottom coverage were obtained from the classification, of which four are homogeneous and eight are mixed coverage. The methodology applied demonstrates that hyperspectral sensors can be used to effectively map submerged vegetation in shallow waters

EHSMu: a new conceptual model for hourly discharge simulation under ecohydrological framework in urban area

A parsimonious conceptual lumped model is presented here with the aim of simulating hourly discharge in urban areas. The EHSMu (EcoHydrological Streamflow Model for urban areas) is able to reproduce the discharge at the outlet of an urban drainage system and, at the same time, soil moisture dynamics and evapotranspirative fluxes over vegetated areas within an urban catchment. In urban areas, rain falling over impervious surfaces is directly transferred towards the drainage system in a time depending on the catchment characteristics, and drainage network geometry. If the rain falls over pervious and vegetated areas the runoff generation is driven by soil moisture content, which in turn is linked to evapotranspiration and leakage. While on one side soil water content determines if rainfall produces saturation excess or a leakage loss, on the other side it constrains the evapotranspirative fluxes, so that, when it approaches to saturation, the actual evapotranspiration tends to the potential one. The hydrological scheme of the urban catchment follows these premises and consists of three interconnected elements: a soil bucket and two linear reservoirs. The soil bucket epitomizes in two distinct classes different conditions within a catchment: the first interprets impervious areas while the second describes pervious and vegetated soils. The soil bucket is linked to the two linear reservoirs: one is responsible for the runoff within the drainage system, while the other is used to delay the entry of subsurface runoff component into the drainage system. The surface reservoir is fed by the rain falling on imperviuos areas, by the saturation excess generated over pervious areas and by the delayed contribution arising from the subsurface reservoir, which is solely supplied by leakage pulses. Soil moisture dynamics in the pervious part of the basin, are simulated by a simple bucket model feed by rainfall and depleted by evapotranspiration. The latter component is calculated as a linear function of soil moisture. The model has been calibrated using Montecarlo simulations on an urban catchment in the United States. This method allows to adapt the conceptual model framework to the catchment characteristics and at the same time to obtain the set of parameters with the higher efficiency in reproducing historical discharge at the outlet. The proposed model gives reliable estimate of runoff, soil moisture traces and evapotranspiration fluxes. Model outputs could be very useful for urban ecohydrology, because they allow for the simulation of vegetation water stress and consequently the design of sustainable urban green spaces. At the same time the model structure allows to simulate the effects of stormwater management best practices for achieving the hydraulic invariance

Regional flow duration curves for ungauged sites in Sicily

Flow duration curves are simple and powerful tools to deal with many hydrological and environmental problems related to water quality assessment, water-use assessment and water allocation. Unfortunately the scarcity of streamflow data enables the use of these instruments only for gauged basins. A regional model is developed here for estimating flow duration curves at ungauged basins in Sicily, Italy. Due to the complex ephemeral behavior of the examined region, this study distinguishes dry periods, when flows are zero, from wet periods using a three parameters power law to describe the frequency distribution of flows. A large dataset of streamflows has been analyzed and the parameters of flow duration curves have been derived for about fifty basins. Regional regression equations have been developed to derive flow duration curves starting from morphological basin characteristics

Using very high resolution (VHR) imagery within a GEOBIA framework for gully mapping: An application to the Calhoun Critical Zone Observatory

Gully erosion is a form of accelerated erosion that may affect soil productivity, restrict land use, and lead to an increase of risk to infrastructure. Accurate mapping of these landforms can be difficult because of the presence of dense canopy and/or the wide spatial extent of some gullies. Even where possible, mapping of gullies through conventional field surveying can be an intensive and expensive activity. The recent widespread availability of very high resolution (VHR) imagery has led to remarkable growth in the availability of terrain information, thus providing a basis for the development of new methodologies for analyzing Earth’s surfaces. This work aims to develop a geographic object-based image analysis to detect and map gullies based on VHR imagery. A 1-meter resolution LIDAR DEM is used to identify gullies. The tool has been calibrated for two relatively large gullies surveyed in the Calhoun Critical Zone Observatory (CCZO) area in the southeastern United States. The developed procedure has been applied and tested on a greater area, corresponding to the Holcombe’s Branch watershed within the CCZO. Results have been compared to previous works conducted over the same area, demonstrating the consistency of the developed procedure

Effetto combinato di cambiamenti climatici ed urbanizzazione sugli estremi di portata

Il termine “cambiamento idrologico” (hydrological change) è spesso utilizzato per sintetizzare quell’insieme di alterazioni della risposta idrologica dei bacini indotte da fattori naturali o antropici. ll ruolo fondamentale di tali alterazioni nel determinare fenomeni di dissesto ha stimolato l’International Association of Hydrological Scienses (IAHS) a dedicare la decade scientifica 2013-2022 (denominata “Phanta Rhei”) ai cambiamenti idrologici e all’analisi dei diversi fattori perturbanti. I cambiamenti climatici e l’urbanizzazione sono fra i fattori antropici perturbanti più influenti e, allo stesso tempo, più diffusi a livello globale. Il cambiamento climatico è stato abbondantemente studiato in passato, con chiare evidenze di trend sugli estremi (es. Burn et al., 2011; Arnone et al., 2013) e con numerosi esempi attestanti i possibili cambiamenti idrologici indotti (es. Wang and Alimohammadi, 2012; Francipane et al., 2015; Chiarelli et al., 2016; Pumo et al. 2016). Molto più recente è l’analisi degli effetti dell’urbanizzazione sulla risposta idrologica dei bacini (es. Salvadore et al., 2015). Il processo di urbanizzazione è associato a una perdita di “superfici permeabili” (suoli naturali), con conseguente impoverimento dei processi d’infiltrazione, alterazione ai sistemi di drenaggio naturale e ai processi di trasferimento (alterazione dei percorsi idrici e delle velocità di deflusso). La valutazione dell’impatto di tali perturbazioni sulle portate di picco durante eventi estremi, può risultare particolarmente utile nel definire e orientare efficaci politiche di pianificazione urbana e gestione di eventi di inondazione, nonché in attività di verifica delle infrastrutture idrauliche esistenti e di progettazione di quelle future. L’obiettivo di questo lavoro è quello di investigare gli effetti dell'interazione delle suddette perturbazioni sugli eventi estremi di deflusso. A tale scopo, è stato ideato un esperimento numerico, applicato ad un piccolo bacino fluviale, che ha permesso di generare e confrontare serie temporali di deflusso orario sotto diversi ipotetici scenari di cambiamento. Gli scenari, generati attraverso l’uso combinato di un modello di cambiamento di uso del suolo opportunamente implementato e di un modello di generazione di serie climatiche già esistente (Fatichi et al., 2011), descrivono situazioni estreme sia in termini di espansione delle aree urbane che in termini di variazioni (aumento o diminuzione) della precipitazione media annua (MAP). Nella creazione degli scenari climatici si è anche tenuto conto di un aumento della temperatura media, e, a parità di MAP, sono state create diverse configurazioni, caratterizzate da diversa frequenza e/o l’intensità media degli eventi di pioggia. La risposta idrologica del bacino ai vari scenari è stata riprodotta mediante il tRIBS (Ivanov et al., 2004), un modello idrologico, fisicamente basato e distribuito, in grado di simulare, con alta risoluzione temporale, anche le diverse componenti di deflusso. I risultati mostrano un’alta sensibilità degli indicatori della risposta idrologica utilizzati alle variazioni delle caratteristiche di pioggia. In termini di deflusso totale, gli effetti dei cambiamenti climatici sembrano essere prevalenti rispetto a quelli indotti dall’espansione urbana, anche se, a una maggiore frazione di suoli impermeabili, corrisponde un chiaro aumento della componente di scorrimento veloce, i cui effetti sul deflusso totale vengono parzialmente smorzati da una simultanea riduzione della componente di deflusso lento e profondo

A paradigm of extreme rainfall pluvial floods in complex urban areas: The flood event of 15 July 2020 in Palermo (Italy)

In the last few years, some regions of the Mediterranean area have witnessed a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events, which are often exacerbated by the ever-growing urbanization. In such a context, the urban drainage systems may not be sufficient to convey the rainwater, thus increasing the risk deriving from the occurrence of such events. This study focuses on a particularly intense urban flood that occurred in Palermo (Italy) on 15 July 2020; it represents a typical pluvial flood due to extreme rainfall on a complex urban area that many cities have experienced in recent years, especially in the Mediterranean region. A conceptual hydrological model and a 2D hydraulic model, particularly suitable for simulations in a very complex urban context, have been used to simulate the event. Results have been qualitatively validated by means of crowdsourced information and satellite images. The experience of Palermo, which has highlighted the urgent need for a shift in the way stormwater in urban settlements is managed, can be assumed to be a paradigm for modeling pluvial floods in complex urban areas under extreme rainfall conditions. Although the approaches and the related policies cannot be identical for all cities, the modeling framework used here to assess the impacts of the event under study and some conclusive remarks could be easily transferred to other, different urban contexts

Definition of Water Meter Substitution Plans based on a Composite Indicator

This paper presents a water meter substitution plan based on a composite "Replacement indicator" which was defined and compared with common substitution strategies based on meter age and on run-to-fail approaches. The methodology was applied to one of the 17 sub-networks in which the Palermo city water distribution network (Italy) is divided. The analysis was carried out considering a substitution budget limitation and the results showed that the use of "Replacement indicator" outperform the classical substitution strategies based on meter age because it takes into account some other variables that may affect meter precision and wearing. (C) 2013 The Authors. Published by Elsevier Ltd

The Effect of Damage Functions on Urban Flood Damage Appraisal

Flooding damage appraisal can been obtained by interpolating real damage data caused by historical flooding events or accounting the effects of a flood in terms of the depreciation of assets. Most often, the expected damage is evaluated by means of damage functions describing the relationship occurring between the damage and hydraulic characteristics of flood. The present paper aims to evaluate the uncertainty linked to the choice of the depth-damage function adopted in the flood damage analysis. Several possible depth-damage function formulations were selected in literature and applied to historical flooding events monitored in the "Centro Storico" catchment in Palermo (Italy). (C) 2013 The Authors. Published by Elsevier Ltd