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Scotland, United Kingdom

Frankl A.,Ghent University | Nyssen J.,Ghent University | De Dapper M.,Ghent University | Haile M.,Mekelle University | And 5 more authors.

In the Highlands of Northern Ethiopia gully occurrence is linked to poverty-driven unsustainable use of the land in a vulnerable semi-arid and mountainous environment, where intensive rainfall challenges the physical integrity of the landscape. Trends in gully and river channel erosion, and their relation to triggering environmental changes can proffer valuable insights into sustainable development in Northern Ethiopia. In order to assess the region-wide change in gully and river channel morphology over 140. years, a set of 57 historical photographs taken in Tigray, and, clearly displaying gully cross-sections, were precisely repeated from 2006 till 2009. Ninety-two percent of the gully and river sections (n. =38) increased in cross-sectional area during the studied period, especially after 1975. Two repeatedly photographed catchments of Lake Ashenge and Atsela allowed a detailed study of gully development from 1936 until 2009. A conceptual hydrogeomorphic model was devised for these catchments and validated for the Northern Ethiopian Highlands. Three major phases can be distinguished in the hydrological regime of the catchments. In the first phase, between 1868 (or earlier) and ca. 1965, the relatively stable channels showed an oversized morphology inherited from a previous period when external forcing in environmental conditions had caused the channels to shape. In the second phase (ca. 1965 - ca. 2000), increased aridity and continued vegetation clearance accelerated the channel dynamics of the gully and river system. The third phase (ca. 2000 - present) started after the large-scale implementation of soil and water conservation measures. In 2009, 23% of the gully and river sections were stabilizing. This paper validates previous research indicating severe land degradation in the second half of the 20th century. Additionally, it demonstrates that the recent erosive cycle started around 1965 and, that at the present time, improved land management stabilizes headwater streams. © 2011 Elsevier B.V. Source

Williams M.A.J.,University of Adelaide | Williams F.M.,University of Adelaide | Duller G.A.T.,Aberystwyth University | Munro R.N.,Old Abbey Associates | And 7 more authors.
Quaternary Science Reviews

Our results show that the late Pleistocene Nile in northern Sudan was shifting position and actively aggrading at 145 ± 20 kyr, 83 ± 24 kyr, 32 ± 8 kyr and 20.7 ± 0.2 kyr and indicate, for the first time, a phase of high-energy flow in the White Nile at 27.8 ± 3.2 kyr, with still high but somewhat reduced flow in that river at 13.3 kyr, 10 kyr and 4.8-4.0 kyr. Beach ridges associated with a 386 m strandline of the White Nile have OSL ages of 27.5 ± 2.7 kyr and 14.5 ± 1.6 kyr. The Holocene terraces and former channels of the main Nile have ages of 11 kyr, 6.5-5.0 kyr and 4.8-4.0 kyr, after which there was a general decline in flood discharge. The now arid main Nile valley in northern Sudan was significantly wetter during the early to middle Holocene, with a lake up to 450 km2 in area, fed by an overflow channel from the early Holocene Nile between 9.5 kyr and 7.5 kyr. Previously stable late Pleistocene dunes were reactivated at intervals during the Holocene, with five samples from the White Nile valley indicating brief phases of Holocene dune activity at 9.9 ± 2.0 kyr, 9.0 ± 2.8 kyr, 6.6 ± 0.9 kyr, 4.8 ± 0.9 kyr and 2.9 ± 0.5 kyr, the earliest of which occurred within periods of generally wetter climate and higher Nile flow. The youngest freshwater shells on the Khor Abu Habl alluvial fan west of the White Nile correspond to a time of regionally wetter climate between 1.7 and 1.0 kyr. Our results suggest that millennial scale climatic instability may have been characteristic of Holocene climates in this region. © 2010 Elsevier Ltd. All rights reserved. Source

Nyssen J.,Ghent University | Frankl A.,Ghent University | Haile M.,Mekelle University | Hurni H.,University of Bern | And 10 more authors.
Science of the Total Environment

As quantitative or spatially distributed studies of environmental change over truly long-term periods of more than 100years are extremely rare, we re-photographed 361 landscapes that appear on historical photographs (1868-1994) within a 40,000km2 study area in northern Ethiopia. Visible evidence of environmental changes apparent from the paired photographs was analyzed using an expert rating system. The conditions of the woody vegetation, soil and water conservation structures and land management were worse in the earlier periods compared to their present conditions. The cover by indigenous trees is a notable exception: it peaked in the 1930s, declined afterwards and then achieved a second peak in the early 21st century. Particularly in areas with greater population densities, there has been a significant increase in woody vegetation and soil and water conservation structures over the course of the study period. We conclude that except for an apparent upward movement of the upper tree limit, the direct human impacts on the environment are overriding the effects of climate change in the north Ethiopian highlands and that the northern Ethiopian highlands are currently greener than at any other time in the last 145years. © 2014 Elsevier B.V. Source

de Muelenaere S.,Ghent University | Frankl A.,Ghent University | Haile M.,Mekelle University | Poesen J.,Catholic University of Leuven | And 4 more authors.
Land Degradation and Development

The combined effects of erosive rains, steep slopes and human land use have caused severe land degradation in the Ethiopian Highlands for several thousand years, but since the 1970s, however, land rehabilitation programmes have been established to try to reverse deterioration. In order to characterize and quantify the transformations in the north Ethiopian Highlands, a study was carried out over 8884km2 of the Tigray Highlands of northern Ethiopia. Using Landsat Multispectral Scanner and later Thematic Mapper imagery (1972, 1984/1986 and 2000), historical terrestrial photographs (1974-1975) and fieldwork (2008), we prepared land use and cover maps. For assessing the use of the historical terrestrial photographs, Landsat images from 1972 were classified using two different methods, namely conventional change detection (image differencing) and ground truthing (using the historical photographs of 1974-1975). Results show that the use of terrestrial photographs is promising, as the classification accuracy based on this method (Kappa coefficient 0·54) is better than the classification accuracy of the method based on image differencing (Kappa coefficient 0·46). Major land use and cover changes indicate the following: (1) a gradual but significant decline in bare ground (32 per cent in 1972 to 8 per cent in 2000); (2) a significant increase of bushland (25 to 43 per cent) and total forest area (including eucalypt plantations, 2·6 to 6·3 per cent); and (3) creation of numerous lakes and ponds. The dominant change trajectory (27 per cent of the study area) indicates a gradual or recent vegetation increase. These changes can be linked to the population growth and the introduction of land rehabilitation initiatives, complemented by growing awareness of land holders. © 2012 John Wiley & Sons, Ltd. Source

Nyssen J.,Ghent University | Frankl A.,Ghent University | Munro R.N.,Old Abbey Associates | Paolo B.,University of Ferrara | And 2 more authors.
Scottish Geographical Journal

The illustrative power of a set of repeat photographs is often stronger than that of other scientific output, but historical photographs are also a very useful research tool and object. Here we demonstrate how historical photographs in Ethiopia are used in studies on landscape and land use changes, soil erosion and geomorphology, history and historical context, livelihood and archaeology. Further, using the case study of Ethiopia, the location, accessibility and quality of digital archives of historical photographs is discussed as well as the way in which they can be used in research. Historical landscape photographs that are available in major archives may now largely be traced and often obtained through the Internet, as libraries increasingly are digitizing collections and making them available online. Institutions that do not make at least part of their collection available online see decreasing numbers of end users, as opposed to a majority of archives which revaluate their collection by making it available online. © 2010 Royal Scottish Geographical Society. Source

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