ANALYSIS OF SPATIO-TEMPORAL DYNAMICS OF AEOLIAN PROCESSES IN ARID AND SEMI-ARID AREAS USING REMOTE SENSING

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Numerically Enhanced Conceptual Modelling (NECoM) applied to the Flumendosa Plain groundwater system (SE Sardinia, Italy)

The alluvial aquifer of the Flumendosa delta plain, in south-eastern Sardinia (Italy), is overexploited for drinking and agriculture purposes and it is subjected to ongoing sea water intrusion phenomena. In a context of progressive quali-quantitative deterioration of groundwater resources, development of a sustainable management plan and, eventually, effective remediation actions require a deep understanding of the investigated system. A systematic review of dataset collected from literature, integrated with new field hydrogeological and geochemical data, is performed to improve the knowledge of the aquifer system. Despite the large amount of processed data, many aspects require further investigations. In this frame, a fast-running steady state groundwater flow numerical model is developed as a tool for testing the preliminary assumptions, to address the main uncertainties, and to optimize the acquisition of new field data. The adopted approach follows the methodology proposed by Lotti et al. (2021) for the development of a Numerically Enhanced Conceptual Model (NECoM). Geometrical discretization of the numerical model is based on results of the 3D hydrogeological reconstruction of the plain area (Arras et al. 2019); simulation of main inflows and outflows, water exchange between surface water bodies and groundwater, irrigation and drinking water withdrawals is performed through the implementation of general head boundaries (GHB), river (RIV), and well (WEL) packages, respectively. Results from the application of the Soil Water Balance code (Porru et al. 2020) are used as input for simulating the average recharge from precipitation. Lateral recharge from the Paleozoic basement is also simulated. More than 4000 heads observations from about 350 wells and piezometers are used as targets in the calibration process; weights are assigned to deal with the high heterogeneity of the dataset quality. RIV and GHB conductance, irrigation well yields, direct and lateral recharge, and hydraulic conductivity are set as parameters in the calibration process. Due to the high sensitivity of some parameters, different calibration cycles are performed; hydraulic conductivities and lateral recharge are then calibrated in the last cycle. Model results show that the hydrogeological conceptualization used for implementing the numerical model can reproduce the main general features of the piezometric head field. According to field observations, the Flumendosa river shows losing conditions in the western part of the plain and next to the river mouth, while gaining conditions occur in its central part; gaining conditions are also observed along the abandoned branches of the Flumendosa river, also known as foxi. Moreover, mass balance analysis show that the Flumendosa river represents the main recharge input of the whole groundwater system, providing an average inflow of about 4.3 Mm3/year. Nevertheless, several local incongruencies with the observed data were precious to highlight the effects of unknown variables such as agricultural extraction wells, the hydrogeological role of the bedrock or the water exchange between surface and groundwater bodies. The discrepancies, rather than the agreements, provided useful direction for the detection of new data to be collected to capture the salient information needed for a proper water resource management

Assessing Recharge Sources and Seawater Intrusion in Coastal Groundwater: A Hydrogeological and Multi-Isotopic Approach

One of the crucial challenges of our time is climate change. The consequences of rising sea levels and drought greatly impact water resources, potentially worsening seawater intrusion. Characterizing coastal aquifers is an essential step in devising strategies to address these phenomena. Seawater intrusion poses a critical socio-economic and environmental issue in the coastal plain of Muravera, southeastern Sardinia (Italy). This coastal plain is an important agricultural area in Sardinia, and the health of the crops is compromised by the increasing salinization of shallow groundwater. To enhance our understanding of the hydrogeological conceptual model, which is essential for a sustainable resource management system, hydrogeological investigations were conducted and complemented by the chemical and multi-isotopic analyses of groundwater. The main objectives of this study were to identify groundwater recharge areas, understand salinization mechanisms and trace the evolution of water chemistry. Within this framework, a monthly survey monitoring piezometric level and electrical conductivity was carried out for one year. This survey was integrated with chemical and isotope analyses, including δ18OH2O and δ2HH2O, δ11B, δ18OSO4, δ34SSO4, and 87Sr/86Sr. Hydrochemistry analysis results revealed the occurrence of seawater–freshwater mixing, extending up to 4 km inland. H2O isotope analysis confirmed the mixing processes and indicated the meteoric origin of recharge waters for both shallow and semi-confined aquifers. The strontium isotopes ratio facilitated the identification of four main groundwater flow paths, confirmed by the SIAR model. The results of this combined hydrogeological–geochemical–isotopic survey provide essential elements for the future implementation of an integrated and sustainable management system. These findings enable interventions to slow the process of seawater intrusion and meet the economic needs for the development of local communities

An interdisciplinary methodology to design integrated and innovative MAR systems in arid and semi-arid regions. Two case studies in Algeria and in Tunisia

Drought,  desertification, Managed Aquifer Recharge (MAR), Tunisia, Algeri

Land Cover Change Modeler: indicatori di trasformazione del territorio come driver per il monitoraggio della salinizzazione in un settore dell’Algeria

Questo studio ha come obiettivo la valutazione del trend spaziale di cambiamento della copertura e uso del suolo in un’area arida e semiarida del Nord Africa, nonché il potenziale di transizione da una classe di copertura del suolo ad un’altra 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 dell’Oued Biskra in Algeria. Lo studio presentato fa parte delle attività 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 un’analisi 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 è stato testato in particolare nel settore dell’Oued 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 all’utilizzo intensivo del territorio per l’agricoltura e in particolare per le coltivazioni di palme da dattero. Inoltre in questi ambienti il clima e le condizioni biofisiche locali hanno un’influenza immediata sulle variazioni di land cover anche con impatto giornaliero, pertanto questo tipo di driver, estremamente variabile, deve essere considerato nella sua dinamicità in modo differente rispetto ai parametri stabili nel tempo quali la morfologia e la litologia e rispetto a quelli a variabilità media come quelli socio-culturali ed economici

A Methodological Approach For The Effective Infiltration Assessment In A Coastal Groundwater

Accurate estimates of spatial and temporal distribution of groundwater recharge are of utmost importance to protect groundwater systems. In coastal areas, the fragility of the systems makes such estimates critical for the correct management and protection of water resources from saltwater intrusion. The Muravera coastal plain, in the south-eastern Sardinia, has been studied since 1960, due to important saltwater intrusion phenomena. Since the early fifties, the natural hydrodynamic equilibrium between groundwater, surface-water and seawater has been deeply modified by the construction of four dams across the Flumendosa river and the development of agriculture, tourism and aquaculture activities along the coast. To implement an integrated and sustainable management system addressed to slow down the process of saltwater intrusion and, on the other, satisfy human requirements, it is important to develop a flexible scenario analysis system that considers changes of land-use and inputs to the hydrogeological system, also in relation to climate change. In this study, the innovative Soil Water Balance code (SWB) has been applied to the Muravera plain groundwater body to calculate spatial and temporal variations of groundwater recharge. The code calculates the recharge (R) by using geographic system (GIS) data layers in combination with tabular climatological data. It is based on a modified Thornthwaite - Mather soil water balance approach, with components of the soil water balance calculated at a daily time-step. A combined experimental approach of hydrogeological, satellite remote sensing and pedological methodologies has been applied to derive data layers describing local features of: (1) land-use classification, (2) hydrologic soil group, (3) flow direction, and (4) soil-water capacity. The code has proved to be promising for the effective infiltration assessment and it can be easily updated with high resolution data acquired in the field and from satellite images

A swift approach for identifying vulnerable linear transport infrastructures in areas prone to floods and erosion

Linear transport infrastructure, such as roads and bridges, is essential for the socio-economic development of industrialized countries, enabling the mobilization of people and goods. However, as these infrastructures extend over wide portions of territories, they are continuously exposed to adverse meteorological and hydrogeological events, including intense rainfall, floods, erosion, and landslides. These events can cause disruptions or malfunctions, leading to significant economic losses. In the last twenty years, floods have represented the natural disaster with the greatest socio-economic impact globally (EM-DAT; http://www.emdat.be/). It is also expected that the frequency and intensity of flood events will increase due to ongoing climate change, consequently escalating the expected impact. In addition to climate change, other factors contributing to increased flood risk include the expansion of urban areas and the extension of large networks of transport infrastructure over potentially flood-prone territories. In this context, studies on the evaluation and implementation of adequate mitigation systems that integrate aspects related to the intrinsic hazardousness of territories and those related to the exposure and vulnerability of elements at risk are of fundamental importance. The objective of this study is to identify portions of the hydrographic network prone to flood and erosion hazards where road infrastructures, such as bridges and/or viaducts, are located. As a test site, the Metropolitan City of Cagliari in southern Sardinia (Italy) has been chosen due to the occurrence of several coastal watersheds with high slope and short corrivation times. After a preliminary bibliographic research on methodological approaches developed in a similar context, the IDRAIM (Rinaldi et al., 2014) approach is applied with some simplifications to be compatible with datasets already available from public repositories (Sardegna Geoportale) and GIS analysis. The methodological approach includes i) the characterization of the physiographic context of the study area and the geomorphological conditions of the hydrographic network through the definition of specific indexes such as the Strahler stream order, confinement conditions, sinuosity index, average slope of homogeneous stream tracts, and average slope of sub-watersheds; ii) a census of stream tracts where bridges were damaged in past flood events and the identification, within the whole study area, of tracts characterized by similar geomorphological indexes; iii) multi-temporal satellite imagery analysis of potentially critical hydrographic network tracts for the identification of flood events and, therefore, the selection of vulnerable road crossings. The adopted methodology represents a useful and fast approach to identify, over wide portion of territories, critical tracts of the hydrographic network where flood and erosion vulnerable road crossings insist. Obtained results can provide the basis of knowledge for the implementation of further field analysis aimed at the detail characterization of infrastructure integrity and magnitude of floods and erosion events. Such information can be of valuable interest in the development of effective climate change adaptation strategies

Assessment of remote sensing-based classification methods for change detection of salt-affected areas (Biskra area, Algeria)

In the Wadi Biskra arid and semiarid areas, sustainable development is restricted by land degradation processes such as secondary salinization of soils. Being an important highquality date production region of Algeria, this area needs continuous monitoring of desertification indicators, hence highly exposed to climate-related risks. Given the limited access to field data, appropriate methods were assessed for the identification and change detection of salt-affected areas, involving image interpretation and automated classifications employing Landsat imagery, ancillary and multisource ground truth data. First, a visual photointerpretation study of the land cover and land use classes was undergone according to acknowledged methodologies. Second, two automated classification approaches were developed: a customized decision tree classification (DTC) and an unsupervised one applied to the principal components of Knepper ratios composite. Five indices were employed in the DTC construction, among which also is a salinity index. The diachronic analysis was undergone for the 1984 to 2015 images (including seasonal approach), being supported by the interpreted land cover/land use map for error estimation. Considering also biophysical and socioeconomic data, comprehensive results are discussed. One of the most important aspects that emerged was that the accelerated expansion of agricultural land in the last three decades has led and continues to contribute to a secondary salinization of soils

Diachronic analysis of salt-Affected areas using remote sensing techniques: the case study of Biskra area, Algeria

In the Wadi Biskra arid and semi-arid area, sustainable development is limited by land degradation, such as secondary salinization of soils. As an important high quality date production region of Algeria, it needs continuous monitoring of desertification indicators, since the bio-physical setting defines it as highly exposed to climate-related risks. For this particular study, for which little ground truth data was possible to acquire, we set up an assessment of appropriate methods for the identification and change detection of salt-affected areas, involving image interpretation and processing techniques employing Landsat imagery. After a first phase consisting of a visual interpretation study of the land cover types, two automated classification approaches were proposed and applied for this specific study: decision tree classification and principal components analysis (PCA) of Knepper ratios. Five of the indices employed in the Decision Tree construction were set up within the current study, among which we propose a salinity index (SMI) for the extraction of highly saline areas. The results of the 1984 to 2014 diachronic analysis of salt - affected areas variation were supported by the interpreted land cover map for accuracy estimation. Connecting the outputs with auxiliary bio-physical and socio-economic data, comprehensive results are discussed, which were indispensable for the understanding of land degradation dynamics and vulnerability to desertification. One aspect that emerged was the fact that the expansion of agricultural land in the last three decades may have led and continue to contribute to a secondary salinization of soils. This study is part of the WADIS-MAR Demonstration Project, funded by the European Commission through the Sustainable Water Integrated Management (SWIM) Program (www.wadismar.eu)