Tectonic background to long-term landform development in tropical Africa

Author(s):  
M. A. Summerfield
2020 ◽  
Author(s):  
Mark Cuthbert ◽  
Richard Taylor

<p>Groundwater is of fundamental importance to strategies for poverty reduction in tropical Africa and understanding the sustainability of more widespread groundwater abstraction for improving water and food provision is a key challenge. However, the hydraulic processes governing groundwater recharge that sustain this resource, and their sensitivity to climatic variability and change, are poorly constrained. Here we present results from The Chronicles Consortium initiative, which has collated multi-decadal groundwater hydrographs and co-located rainfall records across tropical Africa to better understand climate controls, among others, on groundwater recharge.</p><p>We find that recharge in more arid environments is generally highly dependent on infrequent large rainfall events causing focused recharge through losses during ephemeral overland flows. This process is not included in any large scale hydrological or land surface models, and these events are often driven by synoptic climate controls, which are themselves poorly constrained in existing climate models. In more humid locations, we find surprisingly linear relationships between rainfall and recharge indicating an apparent lack of threshold behaviour that is embodied in most hydrological models and hypothesise this is due to prevalence of preferential flow processes in the soil zone. While aridity exerts a strong control on the predominant recharge process, geological variations can dominate the observed sensitivity of recharge to climate variability.</p><p>Our results reveal the critical importance of long-term observational records for understanding the sensitivity of recharge to climate processes with implications well beyond Africa. This especially true in dryland environments where interpretations of short records would miss fundamental, episodic climate-controls on recharge expressed in longer records. We conclude that without a sound long-term observational basis for groundwater-climate sensitivity, climate change forecasts cannot be confidently constrained.</p>


1993 ◽  
Vol 39 (3) ◽  
pp. 300-313 ◽  
Author(s):  
Elise Van Campo ◽  
Francoise Gasse

AbstractAlthough the Tibetan Plateau greatly influences the atmospheric circulation of the Nortbern Hemisphere, few continuous paleoclimatic records are available from the plateau. A 13,000-yr pollen and diatom record from the Sumxi-Longmu Co basin in western Tibet gives information on major changes both in regional vegetation and in local hydrology. After the basin first filled ca. 13,000 yr B.P., a dry spell occurred about 10,500 yr B.P. within the interval spanned by the European Younger Dryas chronozone. A major environmental change occurred suddenly at ≈10,000 yr B.P., with the establishment of wet conditions, and was followed by a long-term trend toward maximum aridity, which lasted approximately 6000 yr. Short-term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr B.P. and a second wet pulse leading to a maximum lake volume ca. 7500-6000 yr B.P. Maximum aridity occurred 4300 yr B.P. The major environmental fluctuations recorded at Sumxi-Longmu Co appear in phase with climatic changes recognized in north tropical Africa, suggesting that the 8000 to 7000-yr-B.P. event was caused by an abrupt disequilibrium in the climatic system, as was the Younger Dryas and possibly the 4300-yr-B.P. event.


1997 ◽  
Vol 38 (1) ◽  
pp. 123-177
Author(s):  
A. D. ROBERTS

The Association of African Universities was formed at Rabat in 1967. In1972 it held a workshop in Accra which resulted in Creating the African University: Emerging Issues of the 1970s (ed. T. M. Yesufu, Ibadan: Oxford University Press, 1973). In 1992, the AAU commissioned the study under review, entrusting it to former vice-chancellors of Lagos and Zambia, and the founding rector of the Université de Bénin. The focus, on universities in tropical Africa, is narrower than the title implies, but of the eleven chapters three consider developments before 1960 and three more survey the next three decades. In part, then, this is a work of history (and certain admirably terse passages of historical summary suggest the hand of the professional historian). It does not, however, claim originality in this respect: inevitably, its earlier sections lean heavily on Ashby, and it has to be said that in general the study is based on a somewhat unsystematic selection of sources. The list of references is disfigured by errors and the index by omissions: it requires much effort to establish, for example, the substantial role of the U.S.A., not only through USAID but through such bodies as the International Council for Educational Development. Still, this is a judicious overview of a large, if depressing, subject, by eminent scholars who are not afraid to criticize their own colleagues as well as governments and outside agencies. ‘The failure of many African academics to fully appreciate the necessity to defend autonomy in the long-term interest of the academy was one of the most enduring legacies of the colonial situation’ (p. 95).


SOIL ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 399-414
Author(s):  
Florian Wilken ◽  
Peter Fiener ◽  
Michael Ketterer ◽  
Katrin Meusburger ◽  
Daniel Iragi Muhindo ◽  
...  

Abstract. Due to the rapidly growing population in tropical Africa, a substantial rise in food demand is predicted in upcoming decades, which will result in higher pressure on soil resources. However, there is limited knowledge on soil redistribution dynamics following land conversion into arable land in tropical Africa that is partly caused by infrastructure limitations for long-term landscape-scale monitoring. In this study, fallout radionuclides 239+240Pu are used to assess soil redistribution along topographic gradients at two cropland sites and at three nearby pristine forest sites located in the DR Congo, Uganda and Rwanda. In the study area, a 239+240Pu baseline inventory is found that is higher than typically expected for tropical regions (mean forest inventory 41 Bq m−2). Pristine forests show no indication of soil redistribution based on 239+240Pu along topographical gradients. In contrast, soil erosion and sedimentation on cropland reached up to 37 cm (81 Mg ha−1 yr−1) and 40 cm (87 Mg ha−1 yr−1) within the last 55 years, respectively. Cropland sites show high intra-slope variability with locations showing severe soil erosion located in direct proximity to sedimentation sites. This study shows the applicability of a valuable method to assess tropical soil redistribution and provides insight into soil degradation rates and patterns in one of the most socio-economically and ecologically vulnerable regions of the world.


Subject Outlook for deforestation in sub-Saharan Africa. Significance The UN Food and Agriculture Organisation's World Forestry Congress last week said that the world has lost 129 million hectares (ha) of forested area since 1990, mainly in tropical Africa and South America. Three of the ten states with the fastest declines since 2010 are in sub-Saharan Africa (SSA), due to demand for wood-fuel and timber for export. Much of the timber is traded illicitly, depriving states of revenue. Impacts Large-scale deforestation could undermine long-term climate change mitigation; forests are critical for absorbing carbon dioxide. The depletion of reserves of rare trees such as Madagascan rosewood will raise its value over time, boosting demand. Gabon's afforestation push -- it has gained 200,000 ha since 2010 due to state programmes -- will support eco-tourism.


2020 ◽  
Author(s):  
Florian Wilken ◽  
Peter Fiener ◽  
Michael Ketterer ◽  
Katrin Meusburger ◽  
Daniel Iragi Muhindo ◽  
...  

Abstract. Due to the rapidly growing population in tropical Africa, a substantial rise in food demand is predicted in upcoming decades, which will result in higher pressure on soil resources. However, there is limited knowledge on soil redistribution dynamics following land conversion to arable land in tropical Africa that is partly caused by challenging local conditions for long-term landscape scale monitoring. In this study, fallout radionuclides 239+240Pu are used to assess soil redistribution along topographic gradients at two cropland sites and at three nearby pristine forest sites located in the DR Congo, Uganda and Rwanda. In the study area, a relatively high 239+240Pu baseline inventory is found (mean forest inventory 41 Bq m−2). Pristine forests show no indication for soil redistribution based on 239+240Pu along topographical gradients. In contrast, soil erosion and sedimentation on cropland reached up to 37 and 40 cm within the last 55 years, respectively. Cropland sites show high intra-slope variability with locations showing severe soil erosion located in direct proximity to sedimentation sites. This study shows the applicability of a valuable method to assess tropical soil redistribution and provides insight on soil degradation rates and patterns in one of the most vulnerable regions of the World.


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