Sinergia de imágenes Sentinel 1 y Sentinel 2 A para la delimitación de humedales a partir de un enfoque ecohidrogeomórfico

In recent years there has been a growing interest in detecting, delimit and inventory wetlands under an ecohydrogeomorphic approach to expand the knowledge of these ecosystems and enable the development of management guidelines for their use. The aim of this article is detect and delimit those sectors that reflect favorable ecohydrogeomorphic conditions to define them as wetlands in a sector of the Alsina basin located in the southwest of the province of Buenos Aires, Argentina. A complementary methodology was applied between optiand radar images, consisting of the use of a digital AlosPalsar elevation model and Sentinel 2 A and Sentinel 1 images. A flood pulse was addressed in the shallow lake that occurred in 2017. The wet events reflect the operation of the shallow lake and the wetland systems. Biophysical changes that occurred in the perilaguna sectors were analyzed in reference to the entry of precipitations. The results verified the presence of different types of wetlands between the shallow lake and its perilagunar area that during a flood function as a hybrid ecosystem.En los últimos años se desarrolla un creciente interés en detectar, delimitar e inventariar humedales bajo un enfoque ecohidrogeomórfico para ampliar el conocimiento de estos ecosistemas y posibilitar la elaboración de lineamientos de gestión para su aprovechamiento. El objetivo de esta investigación es detectar y delimitar aquellos sectores que reflejan condiciones ecohidrogeomórficas favorables para definirlos como humedales en un sector de la cuenca Alsina ubicada en el sudoeste de la provincia de Buenos Aires, Argentina. Se aplicó una metodología complementaria entre imágenes ópticas y radar que consiste en la utilización de un modelo digital de elevación Alos Palsar e imágenes Sentinel 2 A y Sentinel 1. Se abordó un pulso de inundación en la laguna ocurrido en el año 2017. Los eventos húmedos reflejan el funcionamiento de la laguna y los sistemas de humedales. Se analizaron cambios biofísicos que ocurrieron en los sectores perilagunares en referencia al ingreso de lluvias. Los resultados verificaron la presencia de diferentes tipologías de humedales entre la laguna y su área perilagunar que durante una inundación funcionan como un ecosistema híbrido

Multi-risk assessment in a historical city

AbstractNatural hazards pose a significant threat to historical cities which have an authentic and universal value for mankind. This study aims at codifying a multi-risk workflow for seismic and flood hazards, for site-scale applications in historical cities, which provides the Average Annual Loss for buildings within a coherent multi-exposure and multi-vulnerability framework. The proposed methodology includes a multi-risk correlation and joint probability analysis to identify the role of urban development in re-shaping risk components in historical contexts. The workflow is unified by exposure modelling which adopts the same assumptions and parameters. Seismic vulnerability is modelled through an empirical approach by assigning to each building a vulnerability value depending on the European Macroseismic Scale (EMS-98) and modifiers available in literature. Flood vulnerability is modelled by means of stage-damage curves developed for the study area and validated against ex-post damage claims. The method is applied to the city centre of Florence (Italy) listed as UNESCO World Heritage site since 1982. Direct multi-hazard, multi-vulnerability losses are modelled for four probabilistic scenarios. A multi-risk of 3.15 M€/year is estimated for the current situation. In case of adoption of local mitigation measures like floodproofing of basements and installation of steel tie rods, multi-risk reduces to 1.55 M€/yr. The analysis of multi-risk correlation and joint probability distribution shows that the historical evolution of the city centre, from the roman castrum followed by rebuilding in the Middle Ages, the late XIX century and the post WWII, has significantly affected multi-risk in the area. Three identified portions of the study area with a different multi-risk spatial probability distribution highlight that the urban development of the historical city influenced the flood hazard and the seismic vulnerability. The presented multi-risk workflow could be applied to other historical cities and further extended to other natural hazards

ASSESSMENT OF FLOOD HAZARD SUSCEPTIBILITY IN SOUTH SUDAN’S UPPER NILE STATE USING GIS-BASED MULTICRITERIA ANALYSIS

openLe alluvioni sono tra i rischi naturali più rovinosi. I loro effetti avversi comprendono danni alle strutture fisiche, sociali ed economiche, ed un deterioramento dei mezzi di sussistenza. Allo stesso tempo, attribuito alle variazioni climatiche ed eventi estremi causati dal cambiamento climatico, è stato registrato un incremento nella frequenza di alluvioni a livello globale, aumentando la necessita di comprendere gli aspetti spazio-temporali di questi fenomeni. Questo studio esamina la dimensione spaziale del rischio di inondazione nell’Alto Nilo, Sudan del Sud, regione con una riconosciuta vulnerabilità verso le inondazioni, causata principalmente dal suo posizionamento geografico all’interno di una pianura alluvionale caratterizzata da una notevole variabilità della portata di piena. L’obiettivo di questa indagine è quello di mappare la potenziale estensione spaziale degli allagamenti all’interno dell’area di studio in uno scenario di inondazione. La mappa del rischio di inondazioni, fondata su diversi indici, è stata sviluppata utilizzando una decisione d’analisi multicriteriale (MCDA) basata su GIS, ed il analytical hierarchy process (AHP). Gli otto fattori d’influenza per le alluvioni utilizzati per lo studio sono: distanza da fiumi, indice di umidità topografica, densità di drenaggio, copertura del suolo (LULC), precipitazioni medie annue, pendenza, altitudine, e tipo di suolo. La mappa del rischio di inondazione sviluppata per l’area di studio è composta da cinque zone di suscettibilità: molto alta, alta, moderata, bassa, molto bassa. Queste zone coprono rispettivamente il 12%, 26%, 29%, 22%, e 9% dell’area di studio. La mappa è stata ulteriormente validata tramite un confronto con la mappa satellitare dello storico delle inondazioni, ed è risultata soddisfacente nello stimare la probabile estensione spaziale degli allagamenti. Il modello della mappa è potrà risultare strumentale per le misure di preparazione alle inondazioni, e come guida per future indagini specifiche nella dimensione spazio-temporale di eventi alluvionali nella regione dell’Alto Nilo.Floods are among the most ruinous of all natural hazards. Its adverse effects include damages to the physical, social, and economic structures, and disruption of livelihoods. contemporary, attributed to climate change-induced climate variations and extreme weather events, the frequency of flood occurrence has increased all around the globe. This has therefore, augmented the necessity to comprehend the spatial and temporal dimension of flood phenomena. The current study examines the spatial dimension of flood hazard in the Upper Nile state, South Sudan, a region acknowledged to be highly vulnerable to inundation, mainly due to is geographical position within a flood plain characterized by a notable variability in discharge. The objective of this investigation is to map the potential spatial extent of floodwater within the boundaries of study area under flood scenarios. The index-based flood hazard map was developed using GIS-based multicriteria decision analysis (MCDA), and the analytical hierarchy process (AHP). Eight flood influencing factors were used in this study, namely; distance to rivers, topographic wetness index, drainage density, land-coverage (LULC), annual average rainfall, slope, elevation, and soil types. The flood hazard map developed for study area consist of five flood hazard susceptibility zones: very high, high, moderate, low, and very low. These zones encompass proportions of 12%, 26%, 29%, 22%, and 9% of the study area, respectively. The flood hazard map was further validated using satellite historical inundation map and determined to be satisfactory in depicting the probabilistic spatial extent of inundation. The flood hazard model developed is anticipated to be instrumental in pre-flood preparedness measures as well as a guide for future detailed investigations on the spatial–temporal dimension of flood incidents in the Upper Nile state

Flood Hazard Mapping and Assessment on the Angkor World Heritage Site, Cambodia

World Heritage sites in general are exposed to the impacts of natural hazards, which threaten their integrity and may compromise their value. Floods are a severe threat to the Angkor World Heritage site. Studies of regional floods and flood hazard zoning have played an increasingly important role in ensuring sustainability of the Angkor site. This study developed a flood hazard index (FHI) model based on a geographic information system (GIS) and used synthetic aperture radar (SAR) data to extract historical floods at Angkor from 2007 to 2013. Four indices (flood affected frequency, absolute elevation, elevation standard deviation, drainage density) were used to identify flood-prone areas. The Analytic Hierarchy Process (AHP) and the Delphi method were employed to determine the weight of each index. The weighted indices were then used to develop a distribution map of flood hazards at Angkor. The results show that 9 monuments are at risk by potential floods among the 52 components of the Angkor monuments. The high hazard and moderate-to-high hazard areas in the core zone are mainly located surrounding the West Baray but will not bring direct risk impact on the monuments located in the core archaeological zone. The moderate hazard areas are located on both sides of the Siem Reap and Roluos rivers and in the flooded area of the Tonle Sap Lake in the core archaeological zone. These areas cover 19.4 km2, accounting for 9.13% of the total area of the core zone. This moderate hazard zone poses a greater flood threat to the core zone and must be given higher attention. The buffer zone is a small area with fewer sites. As such, flooding has a low impact on the buffer zone. The methods used in this study can be applied to flood hazard assessments of other heritage sites in Southeast Asia