11 research outputs found
Land Cover Change Modeler: indicatori di trasformazione del territorio come driver per il monitoraggio della salinizzazione in un settore dellâAlgeria
Questo studio ha come obiettivo la valutazione del trend spaziale di cambiamento della copertura e uso del suolo in unâarea arida e semiarida del Nord Africa, noncheÌ il potenziale di transizione da una classe di copertura del suolo ad unâaltra considerando vari indicatori ambientali, culturali e socio-economici. Tali indicatori possono costituire i drivers per la costruzione degli scenari di evoluzione spaziale e temporale della salinizzazione dei suoli nel territorio dellâOued Biskra in Algeria. Lo studio presentato fa parte delle attivitaÌ del progetto dimostrativo WADIS-MAR, finanziato dalla Commissione Europea attraverso il Sustainable Water Integrated Management (SWIM) Programme (http://www.wadismar.eu). Partendo dalle mappe di land cover (LC) e salinizzazione elaborate da dati satellitari Landsat, sono stati testati alcuni algoritmi dedicati al Land Change Modeler (LCM). Lo studio si basa su unâanalisi multitemporale di dati Landsat che ha portato allo sviluppo di un classificatore di tipo Decision Tree dedicato al riconoscimento delle aree salinizzate in ambiente arido e semiarido (Melis et al., 2013; Afrasinei et al., 2015). Questo classificatore eÌ stato testato in particolare nel settore dellâOued Biskra (Algeria orientale) lungo il limite settentrionale del sistema morfologico sahariano. La metodologia adottata propone di utilizzare queste mappe come base per la predizione degli scenari di evoluzione del fenomeno della salinizzazione. Tale fenomeno appare fortemente controllato dalle dinamiche sociali ed economiche legate allâutilizzo intensivo del territorio per lâagricoltura e in particolare per le coltivazioni di palme da dattero. Inoltre in questi ambienti il clima e le condizioni biofisiche locali hanno unâinfluenza immediata sulle variazioni di land cover anche con impatto giornaliero, pertanto questo tipo di driver, estremamente variabile, deve essere considerato nella sua dinamicitaÌ in modo differente rispetto ai parametri stabili nel tempo quali la morfologia e la litologia e rispetto a quelli a variabilitaÌ media come quelli socio-culturali ed economici
Study of land degradation and desertification dynamics in North Africa areas using remote sensing techniques
In fragile-ecosystem arid and semi-arid land, climatic variations, water scarcity and human pressure
accelerate ongoing degradation of natural resources. In order to implement sustainable
management, the ecological state of the land must be known and diachronic studies to monitor and
assess desertification processes are indispensable in this respect. The present study is developed in
the frame of WADIS-MAR (www.wadismar.eu). This is one of the five Demonstration Projects
implemented within the Regional Programme âSustainable Water Integrated Management (SWIM)â
(www.swim-sm.eu ), funded by the European Commission and which aims to contribute to the
effective implementation and extensive dissemination of sustainable water management policies
and practices in the Southern Mediterranean Region. The WADIS-MAR Project concerns the
realization of an integrated water harvesting and artificial aquifer recharge techniques in two
watersheds in Maghreb Region: Oued Biskra in Algeria and wadi Oum Zessar in Tunisia.
The WADIS MAR Project is coordinated by the Desertification Research Center of the University
of Sassari in partnership with the University of Barcelona (Spain), Institut des RĂ©gions Arides
(Tunisia) and Agence Nationale des Ressources Hydrauliques (Algeria) and the international
organization Observatorie du Sahara et du Sahel. The project is coordinated by Prof. Giorgio
Ghiglieri. The project aims at the promotion of an integrated, sustainable water harvesting and
agriculture management in two watersheds in Tunisia and Algeria. As agriculture and animal
husbandry are the two main economic activities in these areas, demand and pressure on natural
resources increase in order to cope with increasing populationâs needs. In arid and semiarid study
areas of Algeria and Tunisia, sustainable development of agriculture and resources management
require the understanding of these dynamics as it withstands monitoring of desertification
processes.
Vegetation is the first indicator of decay in the ecosystem functions as it is sensitive to any
disturbance, as well as soil characteristics and dynamics as it is edaphically related to the former.
Satellite remote sensing of land affected by sand encroachment and salinity is a useful tool for
decision support through detection and evaluation of desertification indicating features.
Land cover, land use, soil salinization and sand encroachment are examples of such indicators that
if integrated in a diachronic assessment, can provide quantitative and qualitative information on the
ecological state of the land, particularly degradation tendencies. In recent literature, detecting and
mapping features in saline and sandy environments with remotely sensed imagery has been reported
successful through the use of both multispectral and hyperspectral imagery, yet the limitations to
both image types maintain âno agreed-on best approach to this technology for monitoring and
mapping soil salinity and sand encroachmentâ. Problems regarding the image classification of
features in these particular areas have been reported by several researchers, either with statistical or
neural/connectionist algorithms for both fuzzy and hard classifications methods.
In this research, salt and sand features were assessed through both visual interpretation and
automated classification approaches, employing historical and present Landsat imagery (from 1984
to 2015).
The decision tree analysis was chosen because of its high flexibility of input data range and type,
the easiness of class extraction through non-parametric, multi-stage classification. It makes no a
priori assumption on class distribution, unlike traditional statistical classifiers. The visual
interpretation mapping of land cover and land use was undergone according to acknowledged
standard nomenclature and methodology, such as CORINE land cover or AFRICOVER 2000,
Global Land Cove 2000 etc. The automated one implies a decision tree (DT) classifier and an
unsupervised classification applied to the principal components (PC) extracted from Knepper ratios
composite in order to assess their validity for the change detection analysis. In the Tunisian study
area, it was possible to conduct a thorough ground truth survey resulting in a record of 400 ground
truth points containing several information layers (ground survey sheet information on various land
components, photographs, reports in various file formats) stored within the a shareable standalone
geodatabase. Spectral data were also acquired in situ using the handheld ASD FieldSpec 3 Jr. Full
Range (350 â 2500 nm) spectroradiometer and samples were taken for X-ray diffraction analysis.
The sampling sites were chosen on the basis of a geomorphological analysis, ancillary data and the
previously interpreted land cover/land use map, specifically generated for this study employing
Landsat 7 and 8 imagery. The spectral campaign has enabled the acquisition of spectral reflectance
measurements of 34 points, of which 14 points for saline surfaces (9 samples); 10 points for sand
encroachment areas (10 samples); 3 points for typical vegetation (halophyte and psammophyte) and
7 points for mixed surfaces.
Five of the eleven indices employed in the Decision Tree construction were constructed throughout
the current study, among which we propose also a salinity index (SMI) for the extraction of highly
saline areas. Their application have resulted in an accuracy of more than 80%. For the error
estimation phase, the interpreted land cover/use map (both areas) and ground truth data (Oum
Zessar area only) supported the results of the 1984 to 2014 salt â affected areas diachronic analysis
obtained through both automatic methods. Although IsoDATA classification maps applied to
Knepper ratios Principal Component Analysis has proven its good potential as an approach of fast
automated, user-independent classifier, accuracy assessment has shown that decision tree outstood
it and was proven to have a substantial advantage over the former. The employment of the Decision
Tree classifier has proven to be more flexible and adequate for the extraction of highly and
moderately saline areas and major land cover types, as it allows multi-source information and
higher user control, with an accuracy of more than 80%.
Integrating results with ancillary spatial data, we could argue driving forces, anthropic vs natural, as
well as source areas, and understand and estimate the metrics of desertification processes. In the
Biskra area (Algeria), results indicate that the expansion of irrigated farmland in the past three
decades contributes to an ongoing secondary salinization of soils, with an increase of over 75%. In
the Oum Zessar area (Tunisia), there was substantial change in several landscape components in the
last decades, related to increased anthropic pressure and settlement, agricultural policies and
national development strategies. One of the most concerning aspects is the expansion of sand
encroached areas over the last three decades of around 27%
Evaluation and validation of SRTMGL1 and ASTER GDEM2 for two Maghreb regions (Biskra, Algeria and Medenine, Tunisia)
In this paper, we present the comparison and validation of the Shuttle Radar Topography Mission Version 3.0 Global 1 Arc-Second (SRTMGL1) Digital Elevation Model (DEM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model Version 2 (ASTER GDEM2) applied to two areas of Maghreb region (Biskra, Algeria and Medenine, Tunisia). These are the two target areas assessed in the frame of WADIS-MAR project (http://www.wadismar.eu), which is one of the five demonstration projects implemented within the Regional Programme SWIM (http://www.swim-sm.eu) and funded by the European Commission. Newly released SRTMGL1 is available for free download since October 2014 over the African continent through United States Geological Survey (USGS) web data tools. Given the previously reported issues regarding optical sources DEMs, SRTMGL1 can provide significant advantages in elevation modelling and geoscience applications, but studies regarding its quality assessment and validation are in their early infancy. We employed the two data sets in a visual and quantitative comparison and subsequently, their validation was conducted using ground control points (GCPs) collected within the target areas. Results show that SRTMGL1 presents an overall major accuracy and higher sensitivity to small-scale features and slight variations in landforms
Spatiotemporal and spectral analysis of sand encroachment dynamics in southern Tunisia
Aeolian processes in drylands often transcend into sand encroachment, a common form of land degradation. Highly reflective desert features, hence sandy areas, often cause spectral confusion, and mapping through remote sensing techniques can be challenging. This work aims at designing an efficient classification method that minimises spectral confusion of desert features, hence two types of sandy areas. Moreover, we employ land cover (LC) change detection over the last 30 years. The extraction and spatiotemporal variations of LC and sand encroachment areas in the Dahar-Jeffara Medenine site (southeastern Tunisia) are assessed by employing Landsat imagery (1984 and 2014), a 30 m digital elevation model of Shuttle Radar Topography Mission (SRTMGL 1 arc second), field data and X-ray diffraction analyses of sand samples. Five new spectral indices were designed and employed in a Decision Tree (DT) classifier for the extraction of 11 LC classes, including two different types of sandy areas. The DT map yielded an overall accuracy of around 89%. Change detection results showed substantial change in several landscape components and an increase of sand units by 29% within the Jeffara-Medenine plain over the last three decades. Geomorphological observations and multi-temporal, spectral and mineral analyses indicate a main, possible in-situ source area of sand
Preliminary results of a 3-D groundwater flow model in an arid region of NE Algeria using PMWin: the Inféro-flux phreatic aquifer (Biskra)
Inféro-flux phreatic aquifer (Biskra, NE Algeria) is overexploited for irrigation and drinking water purposes since the fifties. The effect is a quali-quantitative deterioration of the groundwater resources mostly due to an insufficient natural recharge. WADIS-MAR Project aims to the realization of a Managed Aquifer Recharge (MAR) in the Biskra area in order to contribute to re-pressuring the piezometric level of the Inféro-flux. Groundwater flow models can contribute to the understanding of the groundwater behaviour related to the impact of existing and future activities on groundwater resources including the realization of an MAR system. In this work, the preliminary results for a groundwater flow model developed for the Inféro-flux aquifer are presented. They include the model construction and the results of the steady state calibration based on the piezometric head measured in 1966
Metodologia per la caratterizzazione spettrale delle superfici saline e delle aree interessate da aspersioni sabbiose tramite proximal sensing e remote sensing in Tunisia
Lo studio presenta i primi risultati di una ricerca svolta nellâarea di Medenine, Tunisia meridionale,
mirata alla caratterizzazione spettrale delle superfici saline e delle aree interessate da aspersioni
sabbiose, di particolare interesse poichĂš limitano le attivitĂ agro-pastorali. Sono stati acquisiti i dati
spettrali con uno spettroradiometro da campo e parallelamente sono stati prelevati campioni da
sottoporre ad analisi diffrattometriche. I punti di campionamento sono stati scelti sulla base
dellâanalisi morfologica, dei dati spaziali ancillari e della mappatura di copertura/uso del suolo
specificatamente realizzata per questo studio su imagini Landsat 8. Il settore analizzato (400 000
ettari) Ăš stato validato con una campagna a terra di 400 punti di controllo. La campagna spettrale ha
permesso lâacquisizione delle misure di riflettanza di 34 punti, di cui 14 punti per le superfici saline
(con 9 campioni); 10 punti per le aree di aspersioni sabbiose (10 campioni); 3 punti per la
vegetazione specifica (sia alofita, che psammofita) e 7 punti per superfici miste. Le firme spettrali
acquisite sono state elaborate per essere importate nella piattaforma web SPECCHIO per il
confronto con misure acquisite in ambienti simili. Le analisi difrattometriche sono state concluse
per i campioni salini e hanno permesso di definire la componente mineralogica specifica della
risposta spettrale rilevata sul campo. Questo studio propone un modello di analisi spettrale basato
sullâutilizzo integrato di dati acquisiti da proximal e remote sensing finalizzato al monitoraggio dei
fenomeni di land degradation. Lo studio presentato fa parte delle attivitĂ del progetto WADISMAR,
un progetto dimostrativo finanziato dalla Commissione Europea attraverso il Sustainable
Water Integrated Management (SWIM) Programme (http://www.wadismar.eu).This paper presents the preliminary results of a research carried out in the Medenine area,
Southern Tunisia, aimed at the spectral characterization of salt-affected and sand encroachment
areas, as restrictive factors for agro-pastoral activities. Spectral data was acquired in situ using a
handheld spectroradiometer and samples were taken for X-ray diffractometric analysis. The
sampling sites were chosen on the basis of a morphological analysis, ancillary data and a land
cover/land use map specifically generated for this study employing Landsat 8 imagery. The study
area (400 000 hectares) has been validated with 400 ground truth points. The spectral campaign
has enabled the acquisition of spectral reflectance measurements of 34 points, of which 14 points
for saline surfaces (9 samples); 10 points for sand encroachment areas (10 samples); 3 points for
typical vegetation (halophyte and psammophyte) and 7 points for mixed surfaces. The acquired spectral signatures were processed to be integrated into the web platform SPECCHIO for
comparison with measurements acquired in similar environments. Diffractometric analyses were
completed for the saline samples and allowed the identification of the main mineralogical
components. This study proposes a methodology based on the integrated spectral data acquired
through proximal and remote sensing aimed at monitoring of land degradation phenomena. The
study is part of the WADIS-MAR, a demonstration project funded by the European Commission
through the Sustainable Water Integrated Management (SWIM) Programme
(http://www.wadismar.eu)
Classification methods for detecting and evaluating changes in desertification-related features in srid and semi-arid environments
Land cover, land use, soil salinisation and sand encroachment, which are desertification-indicating features, were integrated into a diachronic assessment, obtaining quantitative and qualitative information on the ecological state of the land, particularly degradation tendencies. In arid and semi-arid study areas of Algeria and Tunisia, sustainable development requires the understanding of these dynamics as it withstands the monitoring of desertification processes. Two different classification methods of salt and sand features have been set up, using historical and present Landsat imagery. Mapping of features of interest was achieved using both visual interpretation and automated classification approaches. The automated one implies a decision tree (DT) classifier and an unsupervised classification applied to the principal components (PC) extracted from Knepper ratios composite. Integrating results with ancillary spatial data, we could identify driving forces and estimate the metrics of desertification processes. In the Biskra area (Algeria), it emerged that the expansion of irrigated farmland in the past three decades has been contributing to an ongoing secondary salinisation of soils, with an increase of over 75%. In the Oum Zessar area (Tunisia), there has been a substantial change in several landscape components in the last decades, related to increased anthropic pressure and settlement, agricultural policies and national development strategies. One of the concerning aspects is the expansion of sand encroached areas over the last three decades of around 27%. This work is partly supported and developed within the WADIS-MAR Demonstration Project, funded by the EU Commission through the SWIM Programme (www.âwadismar.âeu)
The SWAT model to assess hydrological processes in arid environment (SE Tunisia), in the frame of WADIS-MAR project
Arid regions of Maghreb (North Africa) suffer scarce water conditions and the erratic behaviour of rainfall events over brief intervals often produce short and intense floods events which converge into ephemeral wadi beds. The watershed of wadi Oum Zessar, in South-East Tunisia, is characterized by a rainfall rate of about 200 mm/year, overexploitation of groundwater resources and is highly exposed to climate change risk and desertification processes (Ghiglieri et al., 2014). This region represents one of the two study areas in the framework of WADIS-MAR demonstration project (www.wadismar.eu), funded by the European Commission under the Regional Programme SWIM (www.swim-sm.eu). WADIS-MAR Project aims: (i) to improve the traditional water harvesting systems (i.e. jessour and tabias) by applying âsoftâ modern rehabilitation interventions; (ii) to increase groundwater availability through managed aquifer recharge (MAR) systems (i.e. gabions, recharge wells, recharge trenches). Jessour andtabias capture surface runoff coming from degraded and rocky rangelands for crop production (fruit trees, mainly olives, and cereals) in upstream subbasins.
The objective of this study was to assess the main hydrological processes and the sediment loads in this arid environment, by using the Soil and Water Assessment Tool (SWAT) model. Sediment load is an important parameter to be considered in the MAR systems because it may causes the clogging of the infiltrating surface, resulting in the reduction of water infiltration rates. The watershed delineation used the newly 2014 released SRTM 1 Arc-Second digital elevation model, available at www.earthexplorer.usgs.gov. A land cover classification obtained by visual interpretation of Landsat data was used for the modelling. Conversion to land use was supported by ancillary and detailed ground truth data.
The classic version of SWAT was adjusted to adapt the model to this dry Mediterranean environment (Ouessar et al., 2009). In SWAT, subbasin may be divided into Hydrologic Response Units (HRUs) which possess unique landuse/management/soil attribute. Normally, the runoff from all HRUs is added directly to the outlet of the subbasin. In this study runoff is routed between HRUs within the subbasin. The main adjustment consists of allowing the simulation of the runoff collection behind the water harvesting structures by bringing the surface runoff and lateral flow generated by different HRUs within the same subbasin. Moreover, existing gabions and recharge wells were considered in the model for a more accurate simulation of the hydrological processes. Possible coupling with MODFLOW will be considered. After calibration and validation, the model will be also used for evaluating the efficiency of the MAR systems which are being realized within the WADIS-MAR project