Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years

2021 ◽  
Author(s):  
Carlo Mologni ◽  
Laurent Bruxelles ◽  
Fabien Arnaud ◽  
Pierre Sabatier ◽  
Anne-Lise Develle ◽  
...  
Keyword(s):  
East African ◽  
Climatic Fluctuations ◽  
Climatic Oscillations ◽  
Sedimentary Records ◽  
Hydrological Changes ◽  
Precession Cycle ◽  
Afar Region ◽  
Geomorphic Features ◽  
Sedimentary System ◽  
The Impact

<p>Throughout the last 14 ka, tropical Africa experienced significant hydrological changes that were mainly driven by the orbital precession cycle, which controls the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that long-term monsoon humid oscillations (African Humid Period / AHP ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity. However, the abrupt or gradual aridification modalities since the end of the AHP and the modalities of the centennial-scale episodes, as well as their impacts on past and current environments are still debated.</p><p>The Lake Abhe basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater originating in the Ethiopian Highlands, and represents a hydro-sedimentary system sensitive to hydro-climatic changes in East Africa. Today it is characterized by residual lakes (Gamari and Afambo lakes) and a hyper-arid climate, while during the AHP, the Abhe basin was occupied by a Mega-lake and by humid environmental conditions. Holocene climatic disruptions drastically changed the landscapes and ways of life along this basin.  </p><p>The aim of this study is to describe, interpret and estimate the impact of hydro-climatic oscillations on the evolution of Lake Abhe’s littoral lacustrine environments and palaeolandscapes since the AHP from different viewpoints.</p><p>Indeed, this research combines paleoclimatological and geomorphological studies based on a new set of <sup>14</sup>C ages on two lacustrine cores and on several morpho-sedimentary outcrops spanning the Early to Late Holocene. Our results allow us to: <strong>a</strong>) refine the temporal occurrence and the hydrological modalities of the AHP including short-term arid episodes linked to Younger Dryas and 8.2 ka North Atlantic events; <strong>b</strong>) recognise some paleo-shoreline geomorphic features linked to lake level fluctuations, as well as the development littoral pedological horizons and the activation/shutdown of the perilacustrine fluvial network during humid and arid events; <strong>c</strong>) track these changes until the present day, and discuss their evolution scenario in the near future.</p><p>Comparing with other regional climatic records, we show how Lake Abhe basin was highly reactive to East African monsoonal regimes, and how current hydrological changes could impact its environments.      </p>

The impact of Dansgaard–Oeschger cycles on the loessic environment and malacofauna of Nussloch (Germany) during the Upper Weichselian

2008 ◽  
Vol 70 (1) ◽  
pp. 91-104 ◽  
Author(s):  
Olivier Moine ◽  
Denis-Didier Rousseau ◽  
Pierre Antoine
Keyword(s):  
Grain Size ◽  
Environmental Changes ◽  
Ice Core ◽  
Schematic Model ◽  
Climatic Fluctuations ◽  
Climatic Oscillations ◽  
The North ◽  
Size Index ◽  
The Impact ◽  
Hygrophilous Species

AbstractA loess sequence has been sampled continuously at high resolution in Nussloch (Rhine Valley, Germany) for malacological and grain-size analyses between ca. 34 and 20 ka. Molluscan abundance and richness, percentage in hygrophilous species and grain-size index show cyclical variations related to the lithological loess–gley alternation. Major molluscan abundance maxima were triggered by temperature increases through an enhancement of the reproduction cycle, whereas cyclical richness fluctuations and percentage in hygrophilous species reflect variations in local humidity and changes in the environmental mosaic. Malacological parameters allow the distinction of four environmental phases organised in cyclical successions correlated with most of the loess–gley doublets. The correlation of the grain-size index of the Nussloch loess sequence with the dust content of the GRIP ice core demonstrates the synchronicity of major molluscan abundance maxima and δ18O increases characterising temperature increases during Dansgaard–Oeschger interstades. A schematic model is proposed to link the North Atlantic Dansgaard–Oeschger climatic oscillations with local environmental changes indicated by both malacofauna and pedostratigraphy. This malacological study of the Nussloch loess sequence thus provides new information about the response of terrestrial loessic palaeoenvironments to millennial-timescale climatic fluctuations during the Upper Weichselian (∼ marine isotope stage 2 (MIS 2) and end of MIS 3).

Climate change and human lakeside adaptation in the Central Afar Region (Lake Abhe basin, Ethiopia & Djibouti) during the Later Stone Age - Neolithic transition: a multi-scalar and multi-proxy approach

2020 ◽  
Author(s):  
Carlo Mologni ◽  
Lamya Khalidi ◽  
Marie Revel ◽  
Laurent Bruxelles ◽  
Jessie Cauliez ◽  
...  
Keyword(s):  
Landscape Patterns ◽  
Lake Basin ◽  
Arid Environments ◽  
Scientific Investigations ◽  
Hydrological Changes ◽  
Afar Region ◽  
First Results ◽  
Hydroclimatic Change ◽  
The Impact ◽  
Humid Period

<p>Throughout the last 20 ka, tropical Africa was the site of significant hydrological changes related to variations in the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that gradual long-term monsoon humid oscillations (African Humid Period ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity (HS1, YD, 8.2 ka, 4.2 ka). These abrupt hydrological changes could have caused drastic transformations in landscape patterns, providing favourable ecosystems, but also produced arid environments that may have restricted human exploitation of the landscape.</p><p>The Abhe Lake basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater and terrigenous inputs from the Ethiopian Highlands, and is a hydro-sedimentary system sensitive to hydroclimatic change. Since 2014, in the context of the VAPOR-Afar and PSPCA programs (in Ethiopia and Djibouti respectively), we have intensified scientific investigations over this basin with the objective of exploring the evolution of Holocene hydroclimatic change, its impact on landscapes and on prehistoric human behaviour during one of the most forcible transitions in human history, that from a dominantly hunter-gathering way of life to the food production societies one.</p><p>We present the first results of this research that combines paleoclimatological, geomorphological and geoarchaeological studies based on a new set of <sup>14</sup>C datations on two lacustrine cores, on several morpho-sedimentary outcrops and on 8 new archaeological sites spanning the Early to Late Holocene. Our results allow us to: <strong>a</strong>) refine the temporal occurrence and the modalities of the African Humid Period and of the 8.2 and 4.2 ka hyperarid episodes, coupling paleolake-level reconstitution and lacustrine sediment analysis (paleolimnology, geochemistry); <strong>b</strong>) evaluate the impact of these hydroclimatic oscillations on perilacustrine sedimentary formation processes, especially for pedogenic formations; <strong>c</strong>) and better understand the relationship between environmental change and the development of one of the most important economic and cultural innovations, that of domestication.  </p>

scholarly journals Epidemic malaria and warmer temperatures in recent decades in an East African highland

2010 ◽  
Vol 278 (1712) ◽  
pp. 1661-1669 ◽  
Author(s):  
David Alonso ◽  
Menno J. Bouma ◽  
Mercedes Pascual
Keyword(s):  
Climate Change ◽  
East Africa ◽  
Nonlinear Response ◽  
Climate Change Impacts ◽  
Human Model ◽  
Recent Past ◽  
East African ◽  
Highly Nonlinear ◽  
The Impact

Climate change impacts on malaria are typically assessed with scenarios for the long-term future. Here we focus instead on the recent past (1970–2003) to address whether warmer temperatures have already increased the incidence of malaria in a highland region of East Africa. Our analyses rely on a new coupled mosquito–human model of malaria, which we use to compare projected disease levels with and without the observed temperature trend. Predicted malaria cases exhibit a highly nonlinear response to warming, with a significant increase from the 1970s to the 1990s, although typical epidemic sizes are below those observed. These findings suggest that climate change has already played an important role in the exacerbation of malaria in this region. As the observed changes in malaria are even larger than those predicted by our model, other factors previously suggested to explain all of the increase in malaria may be enhancing the impact of climate change.

Geochemical Behaviour of Uranium in Sedimentary Formations: Insights From a Natural Analogue Study

2009 ◽  
Author(s):  
Ulrich Noseck ◽  
Vaclava Havlova ◽  
Juhani Suksi ◽  
Thomas Brasser ◽  
Radek Cervinka
Keyword(s):  
Current Knowledge ◽  
Natural Analogue ◽  
Near Surface ◽  
Co2 Partial Pressure ◽  
Long Term Stability ◽  
Reducing Conditions ◽  
Phosphate Mineral ◽  
Sedimentary System ◽  
The Impact

Groundwater data from the natural analogue site Ruprechtov have been evaluated with special emphasis on the uranium behaviour in the so-called uranium-rich clay/lignite horizon. In this horizon in-situ Eh-values in the range of −160 to −280 mV seem to be determined by the SO42−/HS− couple. Under these conditions U(IV) is expected to be the preferential redox state in solution. However, on-site measurements in groundwater from the clay/lignite horizon show only a fraction of about 20% occurring in the reduced state U(IV). Thermodynamic calculations reveal that the high CO2 partial pressure in the clay/lignite horizon can stabilise hexavalent uranium, which explains the occurrence of U(VI). The calculations also indicate that the low uranium concentrations in the range between 0.2 and 2.1μg/l are controlled by amorphous UO2 and/or the U(IV) phosphate mineral ningyoite. This confirms the findings from previous work that the uranium (IV) mineral phases are long-term stable under the reducing conditions in the clay/lignite horizon without any signatures for uranium mobilisation. It supports the current knowledge of the geological development of the site and is also another important indication for the long-term stability of the sedimentary system itself, namely of the reducing geochemical conditions in the near-surface (30m to 60 m deep) clay/lignite horizon. Further work with respect to the impact of changes in redox conditions on the uranium speciation is on the way.

scholarly journals Kenya’s Standard Gauge Railway Project in the Context of Theory and Practice of Regional Planning

2020 ◽  
Vol 10 (2) ◽  
Author(s):  
Leanard Otwori Juma ◽  
Fredrick Adol Gogo ◽  
Ahmed Abduletif Abdulkadr ◽  
Dénes Dávid Lóránt
Keyword(s):  
Regional Planning ◽  
Secondary Data ◽  
Theory And Practice ◽  
Economic Activities ◽  
East African ◽  
African Region ◽  
African Countries ◽  
Transportation Services ◽  
Goods And Services ◽  
The Impact

Despite most African countries having immense natural and human resources potential, the continent has mostly been lagging on matters of economic development. This scenario could primarily be attributed to weak intra-regional and inter-country trade given the poor connectivity, quality, and diversity in transportation services and infrastructure. In this regard, the governments of the greater East African Region representing Tanzania, Rwanda, Burundi, Uganda, South Sudan, Ethiopia and Kenya, therefore, mooted a coordinated vision to develop interlinked regional infrastructure in road and rail transport to allow smooth movement of goods and services.  This paper aimed to critically review the impact of the SGR development on Kenya in the context of regional planning and development. The methodology of the study was a critical review of existing literature and secondary data. Study findings indicated that the development of the (Standard Gauge Railway) SGR is in tandem with the development strategies of other East African Countries. Its development is incorporated in national spatial plans with the rail route targeting regions with viable populations and sustainable economic activities. Criticisms, however, revolve around the ballooning debt to finance infrastructural development and lack of prioritization f mega projects. In conclusion, despite the financial constraints, the SGR is viewed to significantly influence the socio-economic spheres while presenting challenges in the management of landscapes where it traverses in Kenya and the Region.

Riparian Vegetation Dynamic and River Stability on Intermittent Rivers: Impact of Water Transfer Project on Tropical Drylands

2021 ◽  
Author(s):  
Camilla Santos ◽  
Leonardo Dantas Martins ◽  
Kenia Sousa da Cruz ◽  
Jonas Otaviano Praça de Souza
Keyword(s):  
Vegetation Cover ◽  
Riparian Vegetation ◽  
Google Earth ◽  
Water Transfer ◽  
Lateral Stability ◽  
Hydrological Changes ◽  
Vertical Incision ◽  
Short Period ◽  
Geomorphic Units ◽  
The Impact

<p>Rivers on semiarid landscapes typically are characterised by sandy geomorphic units and riverbanks, a natural factor that enhances lateral mobility. Vegetation cover is a crucial factor on lateral instability due to its impact on riverbank and geomorphic units erosion resistance. Nevertheless, riparian vegetation on intermittent and ephemeral channels show growing patterns directly affect by the flow temporality, that controls the water availability. Extended dry intervals hinder the succession ecological on geomorphic units, like bars and islands, and riverbanks and retard the growing process. This work analysed the effects of hydrological changes, caused by one water transfer project, on the bio-geomorphological patterns on riverbanks of a main intermittent river of Brazilian Drylands. Flow data series was used to understand the hydrological pattern changes; Google Earth images and UAV surveys to analyse the vegetation and riverbank behaviour from 2008 to 2020.  Lastly, the identification of riverbank material resistance was based on sedimentology analysis.  The water transfer Project PISF (Projeto de Integração do São Francisco), operating since 2017 March, increase the average flow days from 137,5 to 260/300 days and decreasing the continuous dry period from 200 to 30/45 days. The impact on average annual discharge was slightest, whereas the average water transfer volume was 3m<sup>3</sup>/s. It is essential to highlight the short period of data posterior to the water transfer and the non-regulatiry of water volume transferred; what limits the temporal representativity of the results. There were different types, and level of impacts depending on the river reach characteristics. However, in general, the longer flow permanence increases riparian vegetation density, vertical incision, and lateral stability. Riparian vegetation cover increase, from 20% to 100% on the 9 reaches analysed, across the entire channel, including bedrock reaches, with riverbanks having some rock outcrops percentage. The main changes were on sand bed reaches, that used to have, before 2017, a dynamic braiding pattern, without a clear main incised channel and thalweg shifting. Afterwards, the flow permanence, due to the water transfer project, enabled herbaceous stratus temporal continuity, contributing to surface stability and progressive bushes/trees cover growing. Lastly, the increase in lateral stability, mainly on thalweg position, facilitates the vertical incision on the sand bed reaches, representing 85% of this channel. As a secondary impact, there were necessary, to the road network, built floodway crossings at several points, which changes the channel morphology and the (dis)connectivity process. It can generate distinct channel position and morphology changes causing water and sediment retention upstream and erosion downstream. Lastly, there were slight differences in textural characteristics on riverbanks and geomorphic units, with a rise in fine sediment on the most vegetated areas/units. This analysis reveals that a fast response of riparian vegetation and sand bed reaches morphology, affecting the bio-geomorphological process and all environmental dynamic. It points to fundamental elements which need monitoring after hydrological changes, especially to intermittent and ephemeral rivers.</p>

scholarly journals Local level service delivery, decentralisation and governance: A comparative study of Uganda, Kenya and Tanzania

2009 ◽  
pp. 144-150 ◽  
Author(s):  
Per Tidemand
Keyword(s):  
Service Delivery ◽  
Comparative Study ◽  
Rural Areas ◽  
Basic Education ◽  
Local Level ◽  
East African ◽  
African Countries ◽  
Japan International Cooperation Agency ◽  
Delivery Planning ◽  
The Impact

This paper summarises key findings from a comprehensive analysis commissioned by the Japan International Cooperation Agency (JICA) of the nature of decentralisation in the three East African countries: Kenya, Uganda and Tanzania.The specific objectives of the study were:• Provide a basic comparative analysis of the forms and processes of decentralisation reforms in the three countries• Analyse the specific modalities in the three countries for local service delivery planning and provision within the three sectors of basic education, primary health care and agricultural extension, with a particular emphasis on rural areas. TIDEMAND: Local level service delivery, decentralisation and governance: A comparative study of Uganda, Kenya and Tanzania CJLG May 2009 145• Explore the impact of the specific forms of decentralisation and local level service delivery arrangements in terms of efficiency, accountability (transparency) and democratic process (participation).

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