scholarly journals The Hydro-Isostatic Rebound Related to Megalake Chad (Holocene, Africa): First Numerical Modelling and Significance for Paleo-Shorelines Elevation

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3180
Author(s):  
Anthony Mémin ◽  
Jean-François Ghienne ◽  
Jacques Hinderer ◽  
Claude Roquin ◽  
Mathieu Schuster
Keyword(s):  
Central Africa ◽  
Earth Model ◽  
Lake Chad ◽  
Digital Elevation ◽  
Basin Scale ◽  
Drying Up ◽  
Successful Approach ◽  
Differential Uplift ◽  
Sahel Region ◽  
The Impact

Lake Chad, the largest freshwater lake of north-central Africa and one of the largest lakes of Africa, is the relict of a giant Quaternary lake (i.e., Megalake Chad) that developed during the early- to mid-Holocene African Humid Period. Over the drylands of the Sahara Desert and the semi-arid Sahel region, remote sensing (optical satellite imagery and digital elevation models) proved a successful approach to identify the paleo-shorelines of this giant paleo-lake. Here we present the first attempt to estimate the isostatic response of the lithosphere due to Megalake Chad and its impact on the elevation of these paleo-shorelines. For this purpose, we use the open source TABOO software (University of Urbino, Italy) and test four different Earth models, considering different parameters for the lithosphere and the upper mantle, and the spatial distribution of the water mass. We make the simplification of an instantaneous drying-up of Megalake Chad, and compute the readjustment related to this instant unload. Results (i.e., duration, amplitude, and location of the deformation) are then discussed in the light of four key areas of the basin displaying prominent paleo-shoreline morpho-sedimentary features. Whatever the Earth model and simplification involved in the simulations, this work provides a strong first-order evaluation of the impact on hydro-isostasy of Megalake Chad. It demonstrates that a water body similar to this megalake would induce a significant deformation of the lithosphere in the form of a vertical differential uplift at basin-scale reaching up to 16 m in the deepest part of the paleo-lake, and its shorelines would then be deflected from 2 m (southern shorelines) to 12 m (northern shorelines), with a maximum rate of more than 1 cm y−1. As such, any future study related to the paleo-shorelines of Megalake Chad, should integrate such temporal and spatial variation of their elevations.

scholarly journals Anthropogenic drought dominates groundwater depletion in Iran

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Samaneh Ashraf ◽  
Ali Nazemi ◽  
Amir AghaKouchak
Keyword(s):  
Economic Security ◽  
Groundwater Depletion ◽  
Groundwater Storage ◽  
Rates Of Change ◽  
Level Data ◽  
Basin Scale ◽  
Storage Basin ◽  
Groundwater Reserves ◽  
The Impact ◽  
Hydrological Droughts

AbstractUsing publicly-available average monthly groundwater level data in 478 sub-basins and 30 basins in Iran, we quantify country-wide groundwater depletion in Iran. Natural and anthropogenic elements affecting the dynamics of groundwater storage are taken into account and quantified during the period of 2002–2015. We estimate that the total groundwater depletion in Iran to be ~ 74 km3 during this period with highly localized and variable rates of change at basin and sub-basin scales. The impact of depletion in Iran’s groundwater reserves is already manifested by extreme overdrafts in ~ 77% of Iran’s land area, a growing soil salinity across the entire country, and increasing frequency and extent of land subsidence in Iran’s planes. While meteorological/hydrological droughts act as triggers and intensify the rate of depletion in country-wide groundwater storage, basin-scale groundwater depletions in Iran are mainly caused by extensive human water withdrawals. We warn that continuation of unsustainable groundwater management in Iran can lead to potentially irreversible impacts on land and environment, threatening country’s water, food, socio-economic security.

Searching and Making Meaning of the COVID-19 Pandemic: Perspectives of African Immigrants in the United States

2021 ◽  
pp. 002216782110224
Author(s):  
Angela U. Ekwonye ◽  
Nina Truong
Keyword(s):  
United States ◽  
Health Care Providers ◽  
Meaning Making ◽  
Democratic Republic Of Congo ◽  
Central Africa ◽  
African Immigrants ◽  
The United States ◽  
Care Providers ◽  
Making Meaning ◽  
The Impact

African immigrants continue to be disproportionately affected by the COVID-19 pandemic. It is unclear how they are searching for and finding meaning in the face of this adversity. This study sought to understand how African immigrants in the United States are searching for and making meaning of the COVID-19 pandemic. We conducted in-depth interviews remotely with 20 immigrants from West Africa (Nigeria and Ghana), East Africa (Somali and Rwanda), and Central Africa (Democratic Republic of Congo). The meaning-making model was used as a framework to understand the processes of coping during a significant, adverse life event. The study found that some participants attempted to reduce the impact of the COVID-19 pandemic on their global meaning by seeking answers as to why the pandemic occurred and creating positive illusions. Some redefined their priorities and reframed the pandemic in a positive light. Participants found meaning in the form of accepting the pandemic as a reality of life, appreciating events previously taken for granted, and making positive changes in their lives. This study’s findings can inform health care providers of the meaning-making processes of African immigrants’ and the need to assist them in their search for meaning.

scholarly journals Deep-Down Time: Political Tradition in Central Africa

1989 ◽  
Vol 16 ◽  
pp. 341-362 ◽  
Author(s):  
Jan Vansina
Keyword(s):  
Political Ideology ◽  
Regional Scale ◽  
Central Africa ◽  
Common View ◽  
Historical Processes ◽  
The Social ◽  
The Common ◽  
Political Communities ◽  
The Mind ◽  
The Impact

Around 1850 the peoples of central Africa from Duala to the Kunene River and from the Atlantic to the Great Lakes shared a common view of the universe and a common political ideology. This included assumptions about roles, statuses, symbols, values, and indeed the very notion of legitimate authority. Among the plethora of symbols connected with these views were the leopard or the lion, the sun, the anvil, and the drum, symbolizing respectively the leader as predator, protector, forger of society, and the voice of all. Obviously, in each case the common political ideology was expressed in slightly different views, reflecting the impact of differential historical processes on different peoples. But the common core persisted. The gigantic extent of this phenomenon, encompassing an area equal to two-thirds of the continental United States, baffles the mind. How did it come about? Such a common tradition certainly did not arise independently in each of the hundreds of political communities that existed then. However absorbent and stable this mental political constellation was, it must have taken shape over a profound time depth. How and as a result of what did this happen? Is it even possible to answer such queries in a part of the world that did not generate written records until a few centuries ago or less?This paper addresses this question: how can one trace the social construction of such a common constellation over great time depths and over great regional scale? All the peoples involved are agriculturalists and the political repertory with which we are concerned could not easily exist in its known form outside sedentary societies.

Self-Reported Vision Impairment and Frailty among Older People with Low Cognitive Performance in Central Africa: EPIDEMCA Population-Based Study

2021 ◽  
pp. 1-7
Author(s):  
Antoine Gbessemehlan ◽  
Gilles Kehoua ◽  
Catherine Helmer ◽  
Cécile Delcourt ◽  
Achille Tchalla ◽  
...  
Keyword(s):  
Older People ◽  
Cognitive Performance ◽  
Odds Ratio ◽  
Adjusted Odds Ratio ◽  
Central Africa ◽  
Population Based ◽  
Vision Impairment ◽  
Sub Saharan Africa ◽  
Population Based Study ◽  
The Impact

<b><i>Introduction:</i></b> Very little is known about the impact of vision impairment (VI) on physical health in late-life in sub-Saharan Africa populations, whereas many older people experience it. We investigated the association between self-reported VI and frailty in Central African older people with low cognitive performance. <b><i>Methods:</i></b> It was cross-sectional analysis of data from the Epidemiology of Dementia in Central Africa (EPIDEMCA) population-based study. After screening for cognitive impairment, older people with low cognitive performance were selected. Frailty was assessed using the Study of Osteoporotic Fracture index. Participants who met one of the 3 parameters assessed (unintentional weight loss, inability to do 5 chair stands, and low energy level) were considered as pre-frail, and those who met 2 or more parameters were considered as frail. VI was self-reported. Associations were investigated using multinomial logistic regression models. <b><i>Results:</i></b> Out of 2,002 older people enrolled in EPIDEMCA, 775 (38.7%) had low cognitive performance on the screening test. Of them, 514 participants (sex ratio: 0.25) had available data on VI and frailty and were included in the analyses. In total, 360 (70%) self-reported VI. Prevalence of frailty was estimated at 64.9% [95% confidence interval: 60.9%–69.1%] and 23.7% [95% CI: 20.1%–27.4%] for pre-frailty. After full adjustment, self-reported VI was associated with frailty (adjusted odds ratio = 2.2; 95% CI: 1.1–4.3) but not with pre-frailty (adjusted odds ratio = 1.8; 95% CI: 0.9–3.7). <b><i>Conclusion:</i></b> In Central African older people with low cognitive performance, those who self-reported VI were more likely to experience frailty. Our findings suggest that greater attention should be devoted to VI among this vulnerable population in order to identify early frailty onset and provide adequate care management.

scholarly journals Spatial-temporal changes in river runoff and terrestrial ecosystem water retention under 1.5 °C and 2 °C warming scenarios across China

2017 ◽  
Author(s):  
Ran Zhai ◽  
Fulu Tao ◽  
Zhihui Xu
Keyword(s):  
Climate Change ◽  
Interannual Variability ◽  
River Runoff ◽  
Water Retention ◽  
Terrestrial Ecosystem ◽  
Maximum Temperature ◽  
Climate Scenarios ◽  
Warming Scenario ◽  
Basin Scale ◽  
The Impact

Abstract. The Paris Agreement set a long-term temperature goal of holding the global average temperature increase to below 2.0 ℃ above pre-industrial levels, and pursuing efforts to limit this to 1.5 ℃, it is therefore important to understand the impacts of climate change under 1.5 ℃ and 2.0 ℃ warming scenarios for climate adaptation and mitigation. Here, climate scenarios by four Global Circulation Models (GCMs) for the baseline (2006–2015), 1.5 ℃ and 2.0 ℃ warming scenarios (2106–2115) were used to drive the validated Variable Infiltration Capacity (VIC) hydrological model to investigate the impacts of global warming on river runoff and Terrestrial Ecosystem Water Retention (TEWR) in China. The trends in annual mean temperature, precipitation, river runoff and TEWR were analysed at the grid and basin scale. Results showed that there were large uncertainties in climate scenarios from the different GCMs, which led to large uncertainties in the impact assessment. The differences among the four GCMs were larger than differences between the two warming scenarios. The interannual variability of river runoff increased notably in areas where it was projected to increase, and the interannual variability increased notably from 1.5 ℃ warming scenario to 2.0 ℃ warming scenario. By contrast, TEWR would remain relatively stable. Both extreme low and high river runoff would increase under the two warming scenarios in most areas in China, with high river runoff increasing more. And the risk of extreme river runoff events would be higher under 2.0 ℃ warming scenario than under 1.5 ℃ warming scenario in term of both extent and intensity. River runoff was significantly positively correlated to precipitation, while increase in maximum temperature would generally cause river runoff to decrease through increasing evapotranspiration. Likewise, precipitation also played a dominant role in affecting TEWR. Our findings highlight climate change mitigation and adaptation should be taken to reduce the risks of hydrological extreme events.

scholarly journals An Autocatalytic Network Model of Conceptual Change

2021 ◽  
Author(s):  
Liane Gabora ◽  
Nicole Beckage
Keyword(s):  
Conceptual Change ◽  
Process Model ◽  
Mental Representations ◽  
Pretend Play ◽  
Conceptual Structure ◽  
Earth Model ◽  
Order Effects ◽  
Abstract Thought ◽  
New Information ◽  
The Impact

Reflexively Autocatalytic Foodset-generated (RAF) networks have been used to model the origins of evolutionary processes, both biological (the origin of life) and cultural (the origin of cumulative innovation). The RAF approach tags conceptual shifts with their source, making it uniquely suited to modelling how new ideas grow out of currently available knowledge, studying order effects, and tracking conceptual trajectories within (and across) individuals. Using RAF networks, we develop a step-by-step process model of conceptual change (i.e., the process by which a child becomes an active participant in cultural evolution), focusing on childrens’ mental models of the shape of the earth. Using results from (Vosniadou &amp; Brewer, 1992), we model different trajectories from the flat earth model to the spherical earth model, as well as the impact of other factors, such as pretend play, on cognitive development. As RAFs increase in size and number, they begin to merge and form a maxRAF that bridges previously compartmentalized knowledge. The expanding maxRAF constrains and enables the scaffolding of new conceptual structure. Once most conceptual structure is subsumed by the maxRAF, the child can reliably frame new knowledge and experiences in terms of previous knowledge and experiences, and engage in recursive representational redescription, or abstract thought, at which point the conceptual network becomes a self-organizing structure. The approach distinguishes between mental representations acquired through social learning or individual learning (of existing information), and mental representations obtained through abstract thought (resulting in the generation of new information). We suggest that individual differences in reliance on these information sources culminates in different kinds of conceptual networks and concomitant learning trajectories. These differences may be amplified by differences in the proclivity to spontaneously tailor one’s mode of thought to the situation one is in by modulating the degree of divergence (versus convergence), abstractness (versus concreteness), and context-specificity. We discuss a potential role for the approach in the development of an overarching framework that integrates evolutionary and developmental approaches to cognition.

scholarly journals Government Size and Corruption: A Non-linear Analysis in the Case of EMCCA

2021 ◽  
Vol 12 (4) ◽  
pp. 17
Author(s):  
Assoumou Ondo ◽  
Beau Jency Owono Ondo
Keyword(s):  
Linear Relationship ◽  
Central Government ◽  
Central Africa ◽  
Linear Analysis ◽  
Government Size ◽  
Economic Community ◽  
Non Linear ◽  
The Government ◽  
The Impact ◽  
The Relationship

This article analyzes the relationship between Government size and corruption. Unlike the works in the way which suppose a linear relationship between the two variables, we estimate a panel with change of the modes to characterize the impact of the size of the Central Government on corruption, in the countries of the economic community and monetary of Central Africa (EMCCA). The results show that there is a non-linear relationship between these two variables. Indeed, a strong involvement of the Government in economic activity results in a significant increase in corruption when the Government exceeds a size of 13.5508% of the GDP.

Jihadist Insurgencies in the Sahel

2021 ◽  
pp. 568-586
Author(s):  
Ibrahim Yahaya Ibrahim
Keyword(s):  
Social Relations ◽  
Islamic State ◽  
Boko Haram ◽  
Lake Chad ◽  
Communal Violence ◽  
Governance Model ◽  
Lake Chad Basin ◽  
State And Local ◽  
Sahel Region ◽  
Local Levels

Over the last decade, jihadist violence has expanded and intensified throughout the Sahel region. Jihadi groups, including Boko Haram, Islamic State West Africa Province, Jama’at Nusrat al-Islam wal-Muslimin (JNIM), Katiba Macina, and al-Qaeda in the Islamic Maghreb (AQIM), have established strongholds in many places in the central Sahel, as well as in and around the Lake Chad Basin. As they strengthen their presence, Sahelian jihadists have introduced new changes in local social relations and practices, experimented with new forms of governance, and attempted to insert themselves into the local political economy. Yet, as they gain ground and conquer new spaces, their governance model has also shown its limits: their presence has increasingly fueled deadly communal violence, and infighting among jihadi groups has become recurrent and deadly. This chapter analyses the factors and dynamics behind this surge of jihadi violence in the Sahel. It attempts to situate the global jihadi discourse within the spectrum of Islamic ideologies and discourses and elaborates on the dynamics, both at the state and local levels, that have favored the emergence of jihadi groups.

scholarly journals Effect of DEM Interpolation Neighbourhood on Terrain Factors

2019 ◽  
Vol 8 (1) ◽  
pp. 30 ◽  
Author(s):  
Ying Zhu ◽  
Xuejun Liu ◽  
Jing Zhao ◽  
Jianjun Cao ◽  
Xiaolei Wang ◽  
...  
Keyword(s):  
Interpolation Method ◽  
Simulated Data ◽  
Topographic Features ◽  
Structure And Morphology ◽  
Digital Elevation ◽  
Different Types ◽  
Slope Error ◽  
Elevation Model ◽  
The Impact ◽  
Mls Method

Topographic factors such as slope and aspect are essential parameters in depicting the structure and morphology of a terrain surface. We study the effect of the number of points in the neighbourhood of a digital elevation model (DEM) interpolation method on mean slope, mean aspect, and RMSEs of slope and aspect from the interpolated DEM. As the moving least squares (MLS) method can maintain the inherent properties and other characteristics of a surface, this method is chosen for DEM interpolation. Three areas containing different types of topographic features are selected for study. Simulated data from a Gauss surface is also used for comparison. First, the impact of the number of points on the DEM root mean square error (RMSE) is analysed. The DEM RMSE in the three study areas decreases gradually with the number of points in the neighbourhood. In addition, the effect of the number of points in the neighbourhood on mean slope and mean aspect was studied across varying topographies through regression analysis. The two variables respond differently to changes in terrain. However, the RMSEs of the slope and aspect in all study areas are logarithmically related to the number of points in the neighbourhood and the values decrease uniformly as the number of points in the neighbourhood increases. With more points in the neighbourhood, the RMSEs of the slope and aspect are not sensitive to topography differences and the same trends are observed for the three studied quantities. Results for the Gauss surface are similar. Finally, this study analyses the spatial distribution of slope and aspect errors. The slope error is concentrated in ridges, valleys, steep-slope areas, and ditch edges while the aspect error is concentrated in ridges, valleys, and flat regions. With more points in the neighbourhood, the number of grid cells in which the slope error is greater than 15° is gradually reduced. With similar terrain types and data sources, if the calculation efficiency is not a concern, sufficient points in the spatial autocorrelation range should be analysed in the neighbourhood to maximize the accuracy of the slope and aspect. However, selecting between 10 and 12 points in the neighbourhood is economical.

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