Environmental Remote Sensing and GIS in Tunisia

This chapter presents summaries of the chapters presented in this book. The chapters focus on the use and the role of remote sensing and Geographical systems (GIS) techniques in understanding, monitoring, and investigation of the environmentally related applications in Tunisia. Many case studies are presented. Wide range of topics are covered in the book including information extraction, environmental applications, remote sensing and GIS technologies for modeling, mapping and detecting land use/land cover changes, analyses of land degradation, dryland, drought, as well as to climate change, risks, groundwater vulnerability, and wetlands. All these topics are covered under five themes in 17 chapters including both the introduction and the conclusions chapters.

Among cartographic population density methods, the choropleth method is obviously one of the most used. Two reasons explain this statement: the cartographer’s ease of implementation and the reader’s ease of understanding. Nevertheless, in many cases, this cartographic method may lead to misleading and erroneous results. This happens especially when the case studies reveal high various inner densities, because of the use of calculated density means, the numbers, shapes and sizes of the counting numbers. For spaces observing a high inner heterogeneity, it was proven that the choropleth method has many lacks and deficiencies related in the literature. A few cartographers prefer the dasymetric method based on satellite images since this latter describes more closely the reality of the population distribution even though this method is more difficult to implement. In most cases studies, the dasymetric method was applied to large spaces, whether national or regional, scarcely to urban spaces. The purpose of the chapter book is to give a real idea on the human environment of Tunisia. This will be achieved through the elaboration of a 1:1000000 scale dasymetric map of the population of Tunisia. This map should be the first since similar work on the issue was never achieved on Tunisia. It would portray the great disparities characterizing spaces’ occupation: rural vs urban areas, oasis vs deserts, plains vs mountains, coast vs interior and so on.

Cities in Tunisia are affected by a rapid urban expansion, which has had a significant impact on green space structure. The recent trend of urban policies to preserve green spaces in the context of sustainable urban development has not been able to solve issues. This chapter discusses the problem of green areas reduction and degradation through the case of Sfax city. As an industrial city which suffers from pollution and scarcity of natural space, Sfax needs all its green potential to ensure a better living environment for its citizens. Some spaces still exist but they suffer from deteriorated and degraded conditions and also from the lack of security. Through the use of GIS, the chapter intends to comprehend the spatial effect of urban mutations on green spaces and to assess the natural space in urban planning documents in a city considered as a laboratory for sustainable development. Specific attention is given to the role of local actors, especially civil society, in preserving green spaces and improving citizens’ living environment.

The Meskat system, which is an ancestral anti-erosion practice, has faced abandonment in the last decades. The present study is intended to monitor the spatial and temporal evolution of the Meskat system in the region of Sousse (Tunisian Sahel). Satellite images from the Landsat Thematic Mapper (TM) 5 sensor were used for four years of 1987, 2003, 2007 and 2011. The detection of land use changes was applied with the Geomatica Focus software, based on a supervised classification. Analysis of land use validation and classification highlighted nine land use classes, with an average global success and Kappa indexes of, 86 and 84%, respectively. Results of the space-time evolution of the Meskat system showed that it is mainly divided among three watersheds: Sabkha Halek El Menjel, Wadi Laya El Hammam and Wadi Hamdoun. The diachronic analysis of these three watersheds classification between 1987 and 2011 revealed an expansion of urban areas at the expense of the Meskat system. Indeed, urban areas recorded an increase of 1, 8, and 4%, while areas occupied by Meskat system were decreased by 6, 8, and 13% for the Sabkha Halek El Menjel, Laya El Hammam Wadi and Hamdoun Wadi watersheds, respectively.

Alien plant invasions are getting more widespread and serious at an alarming rate around the world. In Tunisia, many plant species introduced accidently and deliberately have become invasive and continue to engender serious environmental, economic and sanitary problems. Solanum elaeagnifolium Cav. is considered as one of the most widespread invasive weeds in Tunisia, invading a wide range of habitats and generate considerable negatives impacts. Given the potential of its harmful impacts, Solanum elaeagnifolium management has become a high priority for the conservation of ecosystems specially crop fields. Weed mapping is considered the foundation for the development of a strategic long-term management plan to protect agro-biodiversity. In this context, our research consists to provide mapping surveys in a Tunisian arid region to estimate the actual extend of Solanum elaeagnifolium using geographic information system technology in the attempt to generate an accessible geodatabase and to develop a standardized mapping method to track and update weed population dynamics over time.

This work aims to rank the suitable sites for Grombalia aquifer recharge with reclaimed water using PROMETHEE II multicriteria analysis method coupled with Geographical Information System (GIS). The suitable sites were first defined and mapped using the disjunctive/conjunctive method. Then the suitable areas were ranked using the PROMETHEE II method. Several technical, environmental and economic criteria were identified, spatialized, weighted using the AHP method and normalized using the fuzzy functions and then aggregated using the PROMETHEE II method. The best site adapted for Grombalia aquifer recharge with reclaimed water of Bou Argoub wastewater treatment plant (WWTP) was selected. The suitable areas are about 1667 ha, exceeding by far the required area to absorb the amount of effluent produced by the wastewater treatment plant of Bou Argoub. The net flux φ obtained to rank the suitable areas varies between −0.33 and 0.32. The best site is located 3.6 km far from the WWTP, inside an agricultural area and having 9 m unsaturated zone thickness.

The Peninsula of Cap Bon (Tunisia) is an area containing a much-contrasted land use. It is divided into large natural subareas next to the mountains and “artificialized” spaces scattered now along the coast. Yet only a few land use maps have been elaborated on the topic. Within this context, the design and implementation of one specific GIS called LUIS (Land Use Information System) issued from one database may lead to a systemic and “multiscalar” approach to study and understand the complex occupancy of this unique Tunisian region. “Multisource” and “multiscalar” remote sensing images represent certainly the potential source of data and knowledge in this work. The main goal of this research is to develop a methodology that can identify, locate and map, at different scales and by using various modes of presentation, the land use as an overall information system. It contains three phases bringing together a useful synergy between GIS and remote sensing: The design of the LUIS using the HBDS method; Remote sensing image processing. The proper development and implementation of the LUISystem. The data issued from multiple land use layers helps to represent the finest classes of land uses that can be superimposed altogether by creating more or less homogenous subareas. Thus, the various themes which are analyzed, including the social, economic and even historical aspects, ranging from the local to the regional levels. Of course, the LUIS system allows storing, updating, querying and synthesizing heterogeneous data. It also helps to monitor and understand the landscape dynamics, the population changes and the multiple violations of the land use regulations.

The delimitation of so-called sensitive areas is one of the means adopted to prevent contamination of groundwater. This study aims to assess the vulnerability to pollution of Oued Laya shallow aquifer (Central Tunisia) using three parametric approaches linked to Geographic Information System: Standard DRASTIC, Pesticide DRASTIC and Susceptibility Index (SI) methods. According to Standard DRASTIC, the low vulnerability represents the major part of the aquifer, 97%, and the moderate vulnerability, presents only 3% appearing in two small areas in the North-East and South-East. The SI and Pesticide DRASTIC methods however highlight higher susceptibility to pollution. The former assigned 15% to the moderate vulnerability detected in the North-East and South-East and the later allocated 35.5 and 0.5% to the moderate and high vulnerability, observed along the Eastern part and in the North-East part, respectively. Vulnerability methods comparison and spatial distribution of groundwater nitrate content tend to indicate that Pesticide DRASTIC better reflects the specific aquifer vulnerability than SI. Standard DRASTIC, as intrinsic vulnerability method, reflect worst the specific vulnerability to anthropic activities. For the three methods, the most vulnerable parts of the aquifer corresponds to areas subjected to the agricultural pollution from the irrigated lands and to urban contamination, which comes from the wastewater treatment plant (WWTP) of Kalaa Sghira and the uncontrolled landfill located in the Oued Laya river bank close to Akouda. The groundwater protection of Oued Laya aquifer against these pollutions requires removing the uncontrolled landfill and improving the wastewater treatment performance of Kalaa Sghira WWTP.

Nowadays, natural resources are exposed to an increased risk of degradation due to climatic constraints and human pressure. In this context, our research aims to study of the sensitivity of agricultural land in the Abdeladim watershed by mapping the evolution of the hydrographic network (between 1963 and 2016) and assess the susceptibility to soil quality and loss degradation. The objective of this typology was the selection of typical or most representative catchment areas of the Tunisian Dorsale. Among the watersheds studied, the latter is the least watered but the most eroded. It is typical of the aggressiveness of the semi-arid climate of central Tunisia and the sensitivity of the environment to water erosion. To explain this situation, our research was based on a diachronic study of the water system and on a multi-factor study (pedology, slope, land use…) all within the framework of a GIS. Thus, the study of the evolution of the river system (1963–2016) showed a tendency to increase the number of wadis, their length and their width. This development is mainly achieved by the processes and mechanisms of water erosion carried out by concentrated flow (linear, regressive and lateral erosion). This results from the action of two main factors, one is anthropogenic the other is natural. On the other hand, the study of the potential sensitivity of agricultural land in the Abdeladim watershed reveals a growing sensitivity to the degradation of its agricultural potential both by soil loss and by the reduction of quality of the latter. This is the result, on the one hand, of climatic conditions (aridity) and, on the other hand, of anthropogenic use not adapted to the potential of soils. Thus, several measures must be taken to combat the erosion of agricultural land in the Abdeladim watershed. The main aim is to rationalise the human use of soil and water resources and to treat the slopes of waterways by installing anti erosion scheme.

Climate change and urbanization have increased disaster risk in cities and urged the need for effective disaster risk management and risk-informed urban planning. However, up-to-date data that can support risk assessments is often lacking. The ever increasing spatial and temporal resolution of remote sensing sensors offers tremendous opportunities to support risk assessments in cities. In a pilot project for the coastal city of Monastir, Tunisia, multi-temporal optical remote sensing and spatial analysis have been used to support the assessment of current and future exposure, vulnerability, and risk associated with flash floods and coastal erosion. The results were made available in a web-based information system that enables stakeholders to develop response mechanisms and to integrate risk information into urban planning in order to meet the challenges associated with urban disaster risk. The chapter focusses on the role of remote sensing and GIS for urban risk assessments, drawing on lessons from Monastir, and discusses the potential transferability to other urban settings.

Land Use/Land Cover Change (LUCC) is recognized as a crucial driver of environmental change on all spatio-temporal scales. Zarzis region is reputed for its olive groves, vital for its socioeconomic development and because of severe climatic factors, it has a vulnerable ecosystem. Our study focuses on the monitoring of land use dynamics underpinning climate change and on the spatiotemporal assessment of the vigor of olive groves. Analysis of Landsat 5 TM image acquired in 2007 and Landsat 8 OLI image acquired in 2014 was performed under IDRISI software, by a remote sensing-based Land Change Modeler (LCM) method. Our results have shown a clear improvement in the vigor of the olive trees, mainly attributed to an increase in rainfall during the years 2010 and 2012. We have identified areas where land degradation has been attenuated both with Tabias, as a soil and water harvesting technique and with alley cropping between olive trees, as a promising recent agronomic practice. This analytical study is relevant for sustainable development.

Global and regional monitoring of drought are becoming an active research subject during the last decades. In the Middle East and North Africa (MENA) region drought episodes highly control water availability and the functioning of both forested and cultivated ecosystems. The ecohydrologic approach represents a relatively new trend in the holistic assessment of these limited water resources ecosystems as it explains the equilibrium between the components of the soil-vegetation-climate complex. On the other hand, during the last two decades, the models used in the assessment of drought causes and manifestations combine more and more indicators from multi-sensors satellite images. In the present study, the ecohydrology concepts and their methodological basis are presented, and an overview of biophysical and energetic variables derived from remote sensing data at the regional scale are exposed. A general review of the use of remote sensing in ecohydrology during the last two decades is also addressed as well as various methods using satellite images in the ecohydrologic modelling. These methods are divided into two major groups: the direct use of remote sensing in drought and humidity assessment, and the integration of satellite images with other data in water balance models for hydric stress assessment. The ecohydrological modelling integrating remote sensing data makes use of different types of models such as statistical, empirical or physical based models. The availability of free time series satellite images such as MODIS sensors since the year 2000 had allowed the exploration of various models for drought assessment where multispectral images are combined to derive drought indicators of the vegetation in a Tunisian Mediterranean ecosystem. Finally, data quality of time-series images and their calibration and correction are discussed to highlight the required processing for convenient use of these data in drought monitoring at the regional scale.

Land degradation (LD) has become a crucial issue with both environmental and socio‐economic implications. Natural forces, through periodic stresses of extreme and persistent weather events, and human use and abuse of vulnerable areas, jointly affect LD dynamics, creating negative feedbacks for the ecosystem equilibrium. Spatial assessment of environmental phenomena at regional scale involves the analysis and fusion of multiple, complex, multidisciplinary, and large‐scale information. It is thus important to develop cost effective methodologies to assess and monitor dryland conditions. Remote sensing data and geoprocessing are currently widely tested for this purpose as repeatable and spatial cost-effective ideal tool. Meanwhile, standardized techniques and operational procedures still need to be developed to evaluate land degradation and desertification in the arid areas of Mediterranean regions. Changes in surface properties can be detected through remote sensing data analysis. The main sources of information for the large scale monitoring of soils and vegetation is nowadays derived from satellite imaging. Several indices based on visible near-infrared (VNIR) and short-wave infrared (SWIR) reflectance spectrum are used to produce qualitative and quantitative studies of land degradation and desertification through biological, geophysical and chemical properties description. The general objective of this chapter is to present an overview of dryland degradation and to discuss geo-information and remote sensing data analysis as a support tool for the assessment and monitoring of dryland vulnerability in Southeastern Tunisia. Land Use Land Cover (LULC) changes in the Wadi Bouhamed catchment during 1988–2000 and 2000–2011 periods have been evaluated by soil and vegetation radiometric indices (Normalized Difference Vegetation Index-NDVI; Brightness Index-IB) using LANDSAT TM et ETM + images. Data highlighted that desertification is extending downstream the watershed with a sand movement phenomenon. This is mainly explained by long drought events observed since 1988 enhanced by human practices. Starting from the ’80, modification of agricultural activities intensification on the one hand and marginal land abandonment on the other had caused severe environmental impacts, including the increase in land degradation risk.

Future sustainable management of oasis is related to good selected archives of historical dynamics, assessment of actual stats by using earth observation data, and GIS tools. In this study, we combined remote sensing and landscape metrics to monitor the dynamics of Tunisian oasis landscapes, in particular, to characterize land use in the Nefzaoua and Djerid regions. The methodology is based on the analysis of NDVI maps and then through the metrics index analysis using Patch Analyst for oasis class. The application covers a period of thirty-six years from 1979 to 2015 from the processing of Landsat images series. Results reveal an unequally distributed oasis progression in space, with a slightly different rate over the period considered. The increased oasis area was mainly due to uncultivated land cover. However, the analysis of spatial metrics suggests a transition from an accelerated fragmentation phase of the oasis landscape, to an expansion phase by the continuous spreading of existing oasis surfaces. A novelty of this study is that the results observed for landscape metrics can be correlated with a human dimension. The use of Geographical Information System based metric information system and spatial analysis with Inverse Distance Weighted interpolation enabled the future mapping of oasis extension in South Tunisia.

With 17 national parks and 25 nature reserves, Tunisia is a country characterized by great environmental diversity that adopts an environmental policy whose ultimate goal is to ensure the sustainability of natural resources. From this perspective, the study of the ancient and recent dynamics of the environment is a key element in predicting its evolution in the future and the risks they face. This type of study leads to proposals for environmental protection measures. In this context, the study and monitoring of the environmental dynamics of Bou Hema National Park is integrated. The latter is characterized by its economic, geoscientific, historical and cultural value. It is home to the last acacia raddiana forest north of the great Sahara thanks to which has required the classification with UNESCO as a biosphere reserve. The environment of Bou Hedma National Park represents a legacy resulting from a long and complex evolution as evidenced by several morphostructural, chronostratigraphic and anthropogenic indices. These were used for the study and analysis of environmental dynamics. Understanding old environmental evolution is key to understanding and assessing the trend of current dynamics and to estimating sensitivity to potential environmental degradation. Thus, our research has shown that from Pleistocene to the beginning of the historical period, the dynamics of the geomorphological landscape were guided by the interaction of climatic fluctuations, lithology and the morphometry of the watersheds. Currently, environmental dynamics continue to show a trend of erosion resulting in stony paving covering almost the entire pediment. In addition, the environment in Bou Hedma National Park is more sensitive to the potential degradation of soil quality than to the potential degradation to water erosion. In order to limit sensitivity to the degradation of Bou Hedma National Park, it is essential to changes in land-use methods and techniques. This modification could allow for the reduction of soil degradation by water erosion and thus the optimization and sustainability of this natural resource.

Wetlands are the transitional areas between terrestrial and aquatic systems who provide the world with natural storm barriers, environmental cleansers, and food and water resources for many forms of life. However, human interventions have disrupted these ecosystems and caused an important environment damage and 48% of wetlands in the Mediterranean basin have disappeared since 1970. This research aims to study the spatial and temporal evolution of a Tunisian wetland located in the Central-East using earth observation and GIS tools. The diachronic analysis of LULC temporal series of aerial photographs and satellite imagery between 1963 and 2018 showed that the wetlands of big Sfax city underwent important changes explained by coastal industrial activities and the urban sprawl. These factors have led, for example, to the reduction of 85% in the area of the seasonal brackish swamps in the north side of the study area and 55% in the south one, then the transformation of ‘Ezzit’ and ‘El Haffera’ streams to concrete canals.

This concluding chapter contains the significant conclusions and recommendations from all chapters to provide perspective and guidance for student, teachers, researchers, engineers, decision makers, etc. The book topics extend to cover analyses of land degradation, dryland, drought, as well as to climate change, risks, groundwater vulnerability, and wetlands. Conclusions of different Tunisian case studies related to these phenomena using remote sensing and GIS tools are presented and various methodological approaches have been exposed. The presented recommendations strengthen the link between remote sensing and GIS by opening the doors to future applicable and universal research work. Especially recommendations which consist in sensitizing the readers to a technology applied to environmental studies which does not stop evolving at a high speed. The essence of all conclusions and recommendations can be distilled into threads that run throughout this chapter.