Inner Niger Delta Research Articles

Inner Niger Delta Inundation Extent (2010–2022) Based on Landsat Imagery and the Google Earth Engine

The Inner Niger Delta (IND), one of the largest floodplain systems in Africa, sustains the livelihoods of more than three million people and is a driver of the rural economy of Mali as far as agriculture, fish production, and livestock are concerned. Because the IND ecosystem and economy are flood-dependent, it is important to monitor seasonal flooding variations. Many attempts to accomplish this task have relied on detailed datasets, such as daily discharge, daily rainfall, and evapotranspiration, which are not easily accessible for data-sparse areas. Additionally, because the area is large, this remains a challenging task. In this study, the interannual variability of seasonal inundation in the IND was investigated by leveraging the computing power of the Google Earth Engine and its large catalogue of open datasets. The main objective was to analyse the temporal and spatial distributions of the inundation extent during the last 13 years. A collection of Landsat 5, 7, 8, and 9 images were composited and different bands were used with various water and vegetation indices in a pixel-based supervised classification to detect the flood extent between 2010 and 2022. A significant improvement in classification accuracy was observed thanks to the different indices. The results suggest a general increasing trend in the maximum annual inundation extent. Throughout the study period, the maximum inundated area varied between 15,209 km2 in autumn 2011 and 21,536 km2 in autumn 2022. The upstream water intake led to a decrease of about 6–10% of the inundated area. Similar fluctuations in the inundated area, precipitation, and river discharge were observed. The proposed approach demonstrates a great potential for monitoring annual inundation, especially for large areas such as the IND, where in situ measurements are sparse.

Quantification of surface water extent and volume in the Inner Niger Delta (IND) over 2000–2022 using multispectral imagery and radar altimetry

Spatio-temporal dynamics of surface water reservoirs at regional and global scales remain poorly understood. Using satellite remote sensing provides a unique opportunity to address this problem. This study aims to (1) quantify the extent and volume of surface water and (2) compare our approach with other datasets. We utilized MODIS-based spectral indices to monitor temporal variations in inundation extent. By interpolating water levels across the surface water extent, we generated water level maps and quantified surface water volume from 2000 to 2022. Evaluation against ICESat-2 data involved 64 comparisons, with approximately 58% showing an R 2 value greater than or equal to 0.5, and 38% were higher than or equal to 0.7. Compared to the flooding model, our method aligns more closely with ICESat-2 data, contrary to the flooding model which tends to overestimate water levels and, consequently, water storage.

Time Series Analysis of Landsat Images for Monitoring Flooded Areas in the Inner Niger Delta, Mali

Abstract This paper presents an R-based approach to mapping dynamics of the flooded areas in the Inner Niger Delta (IND), Mali, using time series analysis of Landsat 8–9 satellite images. As the largest inland wetland in West Africa, the habitats of IND offers high potential for biodiversity of the flood-dependent eco systems. IND is one of the most productive areas in West Africa. Mapping flooded areas based on satellite images enables to provide strategies for land management and rice planting and modelling vegetation types of IND. Our approach is based on using libraries of R programming language for processing six Landsat images, and each image was taken on November from 2013 to 2022. By capturing spatial and temporal structures of the satellite images on 2013, 2015, 2018, 2020, 2021 and 2022, the remote sensing data are combined to yield estimates of landscape dynamics that is temporally coherent, while helping to analyse fluctuations of spatial extent in fluvial wetlands caused by the hydrological processes of seasonal flooding. Further, by allowing packages of R to support image processing, an approach to mapping vegetation by NDVI, SAVI and EVI indices and visualising changes in distribution of different land cover classes over time is realised. In this context, processing Earth observation data by advanced scripting tools of R language provides new insights into complex interlace of climate-hydrological processes and vegetation responses. Our study contributes to the sustainable management of natural resources and improving knowledge on the functioning of IND ecosystems in Mali, West Africa.

Revisiting site history and regional interaction at the Dia settlement mound complex, Mali

ABSTRACT Previously unpublished results of test excavations in 1986–1987 at Dia, an extensive occupation mound complex on the western margins of the Inland Niger Delta in Mali, have been augmented by a series of new AMS dates. This article explores how the excavation and radiocarbon data together provide new insights into occupation sequences and site formation processes. It presents details on the depositional contexts, chronology and associated material culture at each of the 1986–1987 excavation units. Using these data, we examine the role of post-depositional disturbance, secondary deposition and re-use of earlier cultural deposits in interpreting site formation processes at the Dia settlement mounds. In addition, we emphasise the important role that studies of well-contextualised pottery from excavation can play in evaluating regional interactions through comparisons with other documented sequences in neighbouring areas, including Jenne-jeno and the Méma. This focus on site formation and regional interaction enables new interpretations that also interrogate and expand the results of the larger-scale excavations at Dia by an international team between 1998 and 2002.

Sedimentary and geomorphic evidence of Saharan megalakes: A synthesis

It has long been recognised that the Sahara Desert contains sediment, landform and palaeoecological evidence for phases of increased humidity during the Quaternary period. Many authors have also suggested that during some of these humid periods very large lakes, termed megalakes, developed in several basins within the Sahara. Recent work has questioned their existence. In particular it has been argued that the lack of well-developed and spatially extensive shorelines in these basins suggests that discrete groundwater and spring deposits have been misinterpreted as evidence for megalakes. In this paper we re-evaluate the evidence used to identify megalakes. Firstly, we apply a comprehensive remote sensing and GIS analyses to the megalake shorelines, their catchments and the wider Sahara. This not only supports the previously proposed existence of numerous megalakes, but also indicates a previously unrecognised megalake in the Niger Inland Delta region, here named Megalake Timbuktu. Secondly, we review the geomorphic and sedimentary evidence for the megalakes, highlighting the importance of the sedimentary record in identifying lake highstands, particularly through the example of the Chotts Megalake in southern Tunisia where we provide new sedimentary information on lake shorelines. This analysis demonstrates that in much of the Sahara the dynamic aeolian systems preclude the preservation of well-developed shorelines, but the distribution of fragmented geomorphic features and localised lake deposits provide robust evidence for Quaternary megalake formation. The paper concludes by highlighting that although extensive evidence for Saharan megalake formation exists, the current chronology of lake highstands indicates that the vast majority date to Marine Isotope Stage (MIS) 5 or earlier. Only megalakes Chad and Timbuktu, which derive much of their water from outside the desert, show evidence for Holocene (African Humid Period or AHP) shorelines. The AHP record of the other megalakes indicate the existence of much smaller water bodies than those that developed earlier in the Pleistocene indicating that it was significantly drier than these earlier humid phases.

Resilience of wetland vegetation to recurrent drought in the Inland Niger Delta of Mali from 1982 to 2014

Resilience of wetland vegetation to recurrent drought in the Inland Niger Delta of Mali from 1982 to 2014

Impacts of Fully Coupling Land Surface and Flood Models on the Simulation of Large Wetlands' Water Dynamics: The Case of the Inner Niger Delta

AbstractIt is known that representing wetland dynamics in land surface modeling improves models' capacity to reproduce fluxes and land surface boundary conditions for atmospheric modeling in general circulation models. This study presents the development of the full coupling between the Noah‐MP land surface model (LSM) and the Hydrological Modeling and Analysis Platform (HyMAP) flood model in the NASA Land Information System and its application over the Inner Niger Delta (IND), a well‐known hot‐spot of strong land surface‐atmosphere interactions in West Africa. Here, we define two experiments at 0.02° spatial resolution over 2002–2018 to quantify the impacts of the proposed developments on simulating IND dynamics. One represents the one‐way approach for simulating land surface and flooding processes (1‐WAY), that is, Noah‐MP neglects surface water availability, and the proposed two‐way coupling (2‐WAY), where Noah‐MP takes surface water availability into account in the vertical water and energy balance. Results show that accounting for two‐way interactions between Noah‐MP and HyMAP over IND improves simulations of all selected hydrological variables. Compared to 1‐WAY, evapotranspiration derived from 2‐WAY over flooding zones doubles, increased by 0.8 mm/day, resulting in an additional water loss rate of ∼18,900 km3/year, ∼40% drop of wetland extent during wet seasons, and major improvement in simulated water level variability at multiple locations. Significant soil moisture increase and surface temperature drop were also observed. Wetland outflows decreased by 35%, resulting in a substantial Nash‐Sutcliffe coefficient improvement, from −0.73 to 0.79. It is anticipated that future developments in water monitoring and water‐related disaster warning systems will considerably benefit from these findings.

Effect of rating curve hysteresis on flood extent simulation with a 2D hydrodynamic model: A case study of the Inner Niger Delta, Mali, West Africa

The Inner Niger Delta (IND) is a complex hydraulic system where the flood dynamics and connectivity between water bodies is the main driver for ecosystem services and economic activities. Therefore, it is of pivotal importance that hydraulic models used to assess ecosystem services and socio-economic usages in the IND are capable of capturing both the inundation and connectivity dynamics. A particularity of the IND is that a strong hysteresis effect can be observed in the stage-discharge relationships at all hydrometric stations in the area. However, existing hydrodynamic models of the IND typically use a static stage-discharge relationship as the downstream boundary condition during both the rise and recession of the flood, which leads to potential inaccuracies when trying to predict the flood extent. This paper explores how the simulation results of the flood and connectivity dynamics in the IND can be improved by using a looped rating curve at the downstream model boundary. The looped rating curve is described using the dimensionless discharges and water levels (DLRC) method. The results show that simulation with DLRC improves the accuracy in predicting floodplain extent and connectivity dynamics between the Niger river system and an important lake in the IND. The improvement in water level predictions decreased steadily with the distance from the downstream boundary of the modelled area.

Sustainable Floodplains: Linking E-Flows to Floodplain Management, Ecosystems, and Livelihoods in the Sahel of North Africa

Floodplains are particularly important in the semi-arid region of the Sub-Sahelian Africa. In this region, water governance is still being developed, often without adequate information and technical capacity for good, sustainable water resource management. However, water resources are being allocated for use with minimal sustainability considerations. Environmental flows (e-flows) include the quantity and timing of flows or water levels needed to meet the sustainable requirements of freshwater and estuarine ecosystems. Holistic regional scale e-flows linked to floodplain management can make a noticeable contribution to sustainable floodplain management. The Inner Niger Delta (IND) in Mali is an example of a vulnerable, socio-ecologically important floodplain in the Sahel region of North Africa that is being developed with little understanding of sustainability requirements. Although integrally linked to the Upper Niger River catchment, the IND sustains a million and half people within the region and exports food to surrounding areas. The flooding of the Delta is the engine of the socio-economic development as well as its ecological integrity. This paper aims to demonstrate the contribution that holistic regional e-flow assessment using the PROBFLO approach has to achieving floodplain sustainability. This can be achieved through the determining the e-flow requirements to maintain critical requirements of the ecosystems and associated services used by local vulnerable human communities for subsistence and describing the socio-ecological consequences of altered flows. These outcomes can contribute to the management of the IND. In this study, the socio-ecological consequences of altered flows have been evaluated by assessing the risk of alterations in the volume, duration, and timing of flows, to a number of ecological and social endpoints. Based on the risk posed to these endpoints by each scenario of change, an e-flow of 58% (26,685 million cubic meters (MCM) of water annually) was determined that would protect the ecosystem and maintain indicator components at a sustainable level. These e-flows also provide sustainable services to local communities including products for subsistence and limit any abnormal increases in diseases to the vulnerable African communities who live in the basin. Relative risk outputs for the development scenarios result in low-to-high-risk probabilities for most endpoints. The future development scenarios include insufficient flows to maintain sustainability during dry or low-flow periods with an increase in zero flow possibilities. Although unsuitable during the low-flow or dry periods, sufficient water is available through storage in the basin to meet the e-flows if these scenarios were considered for implementation. The IND is more vulnerable to changes in flows compared to the rivers upstream of the IND. The e-flow outcomes and consequences of altered flow scenarios has contributed to the management of vulnerable IND floodplains and the requirements and trade-off considerations to achieve sustainability.

After the flood and with the people – Late Holocene changes of the woody vegetation in the southwestern Chad Basin, Nigeria

The development of cultivated landscapes under the influence of food production has decisively shaped the composition and appearance of West African savannas as present today. With trees and shrubs forming an important constituent of such landscapes, and its composition characterizing different types of land-use, anthracology is a tool particularly well suited to trace developments and changes through human exploitation of the landscape. Within the West African savanna belts, regions shaped by prolonged annual floods, such as the Middle Senegal Valley, the Inland Niger Delta and the Chad Basin, offer particular ecological preconditions for land-use. We present here a charcoal study for the Chad Basin of northeast Nigeria, demonstrating the special development of a cultivated landscape in an alluvial context. Charcoal samples from stratified Late Stone Age and Iron Age sites within the southwestern Chad Basin, Nigeria were analyzed. Main focus is on the site Mege, spanning more than 2500 years of occupation history. The results are supplemented with and compared to data from other, earlier as well as contemporary sites, in similar or slightly different environments and representing different settlement types, in order to discern general trends. The results illustrate the exploitation of woody vegetation mainly from the clay soils. This is in stark contrast to the results from other regions within the savanna belt, where the vegetation on sandy soils was preferentially exploited for fuel wood. The vegetation changes evidenced through the charcoal assemblages are attributed to reduced flooding as a consequence of falling lake levels during the Late Holocene. Parklands, typical cultivated landscapes of West African savannas, are invisible in the charcoal spectra, and fallow species and useful trees are rarely present. We postulate that the ecological conditions of the floodplain environment have decisively paved a different, less obvious trajectory of cultivated landscape development between 2000 BC and AD 1500 and that the cultivated landscapes present in the region today largely result from the increasing human impact of the last 500 years.

Caravans of Gold, Fragments in Time: Art, Culture, and Exchange Across Medieval Saharan Africa edited by Kathleen Bickford Berzock

Caravans of Gold, Fragments in Time: Art, Culture, and Exchange Across Medieval Saharan Africa edited by Kathleen Bickford Berzock

Development of a time-varying MODIS/ 2D hydrodynamic model relationship between water levels and flooded areas in the Inner Niger Delta, Mali, West Africa

Study regionThe Inner Niger Delta (IND), Mali, West Africa, is a vast floodplain with abundant natural resources that supports the livelihood of about two million people. Ecosystem services in the IND are strongly affected by flood dynamics. Study focusAn accessible yet accurate flood extent estimation method is crucial for the management of natural resources in the IND. The relationships between water levels and inundation extents are examined for both the rising and receding flood periods, using the outputs of a 2D hydrodynamic model. Inundation extents derived from MODIS images were used to validate the result. New hydrological insight for the regionThe relationship between water levels and flooded areas in the IND changes from year to year due to the amplitude of the incoming flood. Equations were developed to capture that dynamic relationship and estimate flood extent in real-time from September to the end of flood using water levels at Mopti. The relationship is dependent on the maximum water level at Mopti and maximum flooded area which was forecasted using streamflow and precipitation in the Upper Niger Basin. Results show that in addition to forecasting the maximum inundation ahead of time, the inundation predicted with the method shows improvement over the existing formulas by Mahé et al. (2011), Zwart et al. (2005), and Mariko (2003).

Challenges and Opportunities in the Operationalization of the Water-Environment-Energy-Food (WE2F) Nexus: Case Study of the Upper Niger Basin and Inner Niger Delta, West Africa

The ever-increasing demand for water, food, and energy is putting unsustainable pressure on natural resources worldwide, often leading to environmental degradation that, in turn, affect water, food, and energy security. The recognition of the complex interlinkages between multiple sectors has led to the creation of various holistic approaches to environmental decision making such as Integrated Natural Resources Management (INRM), Integrated Water Resources Management (IWRM), Virtual Water (VW), Water Footprint (WF) and lately the Food-EnergyEnvironment-Water nexus (WE2F). All these approaches aim to increase resource use efficiency and promote sustainability by increasing the cooperation between traditionally disjoint sectors, and mainly differ by the number and relative weights of the sectors included in their framework. They also suffer from the same face and the same barriers for implementation, some of which may never be fully overcome. The paper discusses the benefits of adopting a WE2F nexus approach in the Upper Niger Basin (UNB) and the Inner Niger Delta (IND), but also the multiple difficulties associated with its practical implementation. IWRM/WE2F initiatives in the UNB/IND such as the BAMGIRE project piloted by Wetlands International and funded by the Dutch Embassy in Mali to secure livelihoods and biodiversity in a changing environment, is taken as an example of partial success in the use of a nexus approach to watershed management. It was shown there are multiple barriers to the operational implementation of the WE2F. However, while a full understanding of all interlinkage between sectors may never be possible, data collection, scientific research and model development can improve our ability to understand the complex system in which we live, and hence take better decisions

Improving the Accuracy of Hydrodynamic Simulations in Data Scarce Environments Using Bayesian Model Averaging: A Case Study of the Inner Niger Delta, Mali, West Africa

In this paper, the study area was the Inner Niger Delta (IND) in Mali, West Africa. The IND is threatened by climate change, increasing irrigation, and dam operations. 2D hydrodynamic modelling was used to simulate water levels, discharge, and inundation extent in the IND. Three different digital elevation models (DEM) (SRTM, MERIT, and a DEM derived from satellite images were used as a source of elevation data. Six different models were created, with different sources of elevation data and different downstream boundary conditions. Given that the performance of the models varies according to the location in the IND, the variable under consideration and the performance criteria, Bayesian Model Averaging (BMA) was used to assess the relative performance of each of the six models. The BMA weights, along with deterministic performance measures, such as the Nash Sutcliffe coefficient (NS) and the Pearson’s correlation coefficient (r), provide quantitative evidence as to which model is the best when simulating a particular hydraulic variable at a particular location. After the models were combined with BMA, both discharge and water levels could be simulated with reasonable precision (NS > 0.8). The results of this work can contribute to the more efficient management of water resources in the IND.

Evolution of the Performances of Radar Altimetry Missions from ERS-2 to Sentinel-3A over the Inner Niger Delta

Radar altimetry provides unique information on water stages of inland hydro-systems. In this study, the performance of seven altimetry missions, among the most commonly used in land hydrology (i.e., European Remote-Sensing Satellite-2 (ERS-2), ENVIronment SATellite (ENVISAT), Satellite with Argos and ALtika (SARAL), Jason-1, Jason-2, Jason-3 and Sentinel-3A), are assessed using records from a dense in situ network composed of 19 gauge stations in the Inner Niger Delta (IND) from 1995 to 2017. Results show an overall very good agreement between altimetry-based and in situ water levels with correlation coefficient (R) greater than 0.8 in 80% of the cases and Root Mean Square Error (RMSE) lower than 0.4 m in 48% of cases. Better agreement is found for the recently launched missions such as SARAL, Jason-3 and Sentinel-3A than for former missions, indicating the advance of the use of the Ka-band for SARAL and of the Synthetic-aperture Radar (SAR) mode for Sentinel-3A. Cross-correlation analysis performed between water levels from the same altimetry mission leads to time-lags between the upstream and the downstream part of the Inner Niger Delta of around two months that can be related to the time residence of water in the drainage area.

Finding the ephemeral: Herding strategies and socio-economic organization in an urban West African context

In this paper, I use zooarchaeological data to investigate the relationship between food production strategies, particularly herding practices, and socioeconomic configurations in the ancient city of Jenné-jeno (occupied ca. 250 BCE to 1400 CE) and in archaeological contexts (ca. 1400–1900 CE) from the modern city of Djenné, both located in Mali's Inland Niger Delta (IND). IND populations are notable for their system of subsistence specialization, wherein self-ascribed ethnic groups identify strongly with specific subsistence regimes. This organization is a successful response to the area's unpredictability and, as such, exerts strong influence on interpretations of many IND archaeological contexts. In particular, scholars have invoked subsistence specialization as a possible underlying explanation for the distinctive social and political organization found at Jenné-jeno, most notably in Rod McIntosh's Pulse Model. Data from osteometric and isotopic (87Sr/86Sr) analysis of domestic herd animals, however, suggest that subsistence regimes were much more diversified at Jenné-jeno and neighboring sites, and that ethnically-linked subsistence specialization may have emerged in this area only as part of a broad social, political, and settlement pattern reorganization coincident with Jenné-jeno's abandonment. I argue that despite facing broadly similar climatic uncertainty over the past two millennia, populations in and around Jenné-jeno adopted shifting social and economic strategies, with new approaches emerging in the face of specific environmental challenges and changing social contexts. This study joins others in showing the extent to which ancient urban centers are the product of their local environmental and sociopolitical settings, rather than conforming to expected models of urban configurations.

Water Balance Analysis over the Niger Inland Delta-Mali: Spatio-Temporal Dynamics of the Flooded Area and Water Losses

The Niger Inland Delta (NID) wetland comprises a large flooded area that plays an important role in the ecosystem services. This study provides a comprehensive understanding of the NID’s hydro-climatological functioning using water balance approach. After a clear description of the water budget’s elements specific to the NID catchment, a spatial and temporal dynamics of the annual flood across the NID over the period 2000–2009 was performed using data from satellite QuickSCAT and its associated sensor SeaWinds. The estimated areas were used along with observed discharge and remotely-sensed climatic data to quantitatively evaluate each water balance component. The results indicate: (i) a clear spatiotemporal of the flooded areas varied between 25,000 km2 in wet periods and 2000 km2 in dry periods; (ii) an average evapotranspiration loss of 17.31 km3 (43% of the total inflow) was assessed in the catchment; (iii) precipitation’s contribution to the NID’s budget totals 5.16 km3 (12.8% of the total inflow); and (iv) the contribution of return flow from irrigated fields totals 1.8 km3 (4.5% of the total inflow, among which 1.2 km3 are from Office du Niger) to the flooded areas, refined the NID’s water balance estimates. Knowledge gained on NID’s water balance analysis will be used to develop and calibrate hydrological models in the Niger Inland Delta of the basin.

C. J. Stevens, S. Nixon, M. A. Murray, and D. Q. Fuller (eds): Archaeology of African Plant Use

This volume is the outcome of the Fifth International Workshop for African Archaeobotany, held in London in July 2006. About half of the papers are those presented at theWorkshop. In addition, about an equal number of papers commissioned carefully by the editors have been included to provide a comprehensive picture of the entire field of African archaeobotany including plant use. The timelapse in bringing out this volume may be attributable to the decision of the editors to make this volume a comprehensive one on African archaeobotany. The editors appear to have succeeded in their efforts. There are 23 chapters in the volume. It has been edited by C.J. Stevens (Research Associate, Institute of Archaeology, University College, London), S. Nixon (Associate, Institute of Archaeology, UCL), M. A. Murray (Archaeobotanist, University of Copenhagen), and D.Q. Fuller (Professor of Archaeobotany, Institute of Archaeology, U.C.L). The IWAA (International Workshops on Archaeobotany) have been organized once every 3 years since 1994. All their proceedings have been published. Each of these meetings has brought in newer approaches, broader perspectives, and/or different realms into the studies on paleoand archaeobotany of Africa. At the same time, they have revealed the stark fact that half the continent of Africa continues to remain totally unexplored, and even in the regions where some work has been done, only minimal work has been carried out., except in two countries/regions—Egypt and Inland Niger Delta (IND) in west Africa. Chapter 1 gives a synopsis of these Workshops. Africa, with 30 million km area, is the second largest and second most populous continent in the world after Asia, with 20 % land area of the world and 1.1 billion population, against Asia’s 30 % land area and 4.3 billion people. It stretches north to south from 36 N and 34 S Latitude. It encompasses a very wide range of physical features and ecological regions comprising deserts, including the Sahara, savannas, subtropical flatlands, woodlands, and tropical forests. Africa was the home of the first hominids. Egypt in northeastern Africa is one of the earliest centres of human civilization. However, most archaeologists assume that Egypt is a ‘quite separate realm’. There are 23 chapters in the book. The first chapter is an ‘editorial’ by the authors of the volume. It first gives a brief historical account of the early botanical and genetic studies done on African plants origins beginning with Vavilov. It is followed by a more detailed and analytical account of the archaeological studies done in Africa till date. This includes also accounts of all the IWAA Workshops held so far. They reveal the very low intensity and coverage of the studies done in the continent except in Egypt, basing it N. M. Nayar (&) JN Tropical Botanic Garden and Research Institute, Palode, Trivandrum 695 582, Kerala, India e-mail: nayar.nm@gmail.com

Coring Lake Fati and Settlement Archaeology of the Middle Niger Lakes Region

A two-part archaeological and limnological study of the Malian Lakes Region has revealed the high research potential of the region. The exploratory reconnaissance of the Gorbi Valley, on the eastern edge of Lake Fati, identified, mapped and sampled eight new sites. The results of the survey suggest a long duration occupation of the Gorbi Valley, as well as possible connections with the populations of the Inland Niger Delta and southeastern Mauritania. The Lake Fati core represents the first lake sediment core from the western Sahel. This 5.4 m sediment core contains a continuous record of lake mud from 10.43 to 4.66 kyr BP. Analysis of the core reveals that Al and Si abundances are decoupled following a deposition of 16 cm of sand at 4.5 ka BP, with Al decreasing and Si increasing rapidly. This period of sand deposition is significantly younger than that of the transition at 5.5 ka BP recorded in marine cores from ODP site 658, taken off the Mauritanian coast, potentially extending the timeframe in which dune systems were stable and lake systems were at their highstand. While highlighting the need for more localized climate chronologies and archaeological investigations, this study may shed light on circumstances surrounding the initial colonization and further development of the Lakes Region.

Inundations in the Inner Niger Delta: Monitoring and Analysis Using MODIS and Global Precipitation Datasets

A method of wetland mapping and flood survey based on satellite optical imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra instrument was used over the Inner Niger Delta (IND) from 2000–2013. It has allowed us to describe the phenomenon of inundations in the delta and to decompose the flooded areas in the IND into open water and mixture of water and dry land, and that aquatic vegetation is separated from bare soil and “dry” vegetation. An Empirical Orthogonal Function (EOF) analysis of the MODIS data and precipitation rates from a global gridded data set is carried out. Connections between flood sequence and precipitation patterns from the upstream part of the Niger and Bani river watersheds up to the IND are studied. We have shown that inter-annual variability of flood dominates over the IND and we have estimated that the surface extent of open water varies by a factor of four between dry and wet years. We finally observed an increase in vegetation over the 14 years of study and a slight decrease of open water.