Small-scale aerial photographs and high-resolution satellite images, 23 available for Ethiopia since the second half of the 20th century as for most countries, 24 allow only to determine the length of gullies in detail. Understanding the development of 25 gully volume therefore requires to establish empirical relations between gully volume (V) 26 and length (L) in the field. So far, such V -L relations were proposed for a limited 27 number of gullies/environments and were especially developed for ephemeral gullies. In 28 this study, V -L relations were established for permanent gullies in Northern Ethiopia, 29 having a total length of 152 km. In order to take the regional variability in environmental 30 characteristics into account, factors that control gully cross-sectional morphology were 31 studied from 811 cross-sections. This indicated that the lithology and the presence of 32 check dams or low-active channels were the most important controls of gully cross-33 sectional shape and size. Cross-sectional size could be fairly well predicted by their 34 drainage area. The V -L relation for the complete dataset was V = 0.562 L 1.381 (n = 33, 35 r² = 0.94, with 34.9% of the network having check dams and/or being low-active). 36 Producing such relations for the different lithologies and percentages of the gully 37 network having check dams and/or being low-active allows to assess historical gully 38 development from historical remote sensing data. In addition, gully volume was also 39 related to its catchments area (A) and catchment slope gradient (S c ). This study 40 demonstrates that V -L and V -A x S c relations can be very suitable for planners to 41 assess gully volume, but that the establishment of such relations is necessarily region-42 specific. 43 44

High‐altitude forests are very important for local livelihood in the vulnerable environment of the densely populated tropical highlands. Humans need the ecosystem services of the forest and directly impact the forest through livestock herding, fire, and wood harvesting. Nevertheless, temperature‐sensitive tree lines in the tropics are scarcely investigated in comparison with higher northern latitudes. In this study, the Erica arborea L. tree line is studied in a tropical mountain in the North Ethiopian highlands: Lib Amba of the Abune Yosef Mountain range (12°04′N, 39°22′E, 3993 m asl). The present tree line and forest cover was recorded by high‐resolution satellite imagery from Google Maps and field data (2010–2013), while historical forest cover was studied from aerial photographs (1965–1982) and repeat photography (1917–2013). The aerial and satellite images were orthorectified and classified in forest/non‐forest binary maps. The binary forest layers were used to detect forest‐cover change and tree line dynamics by image differencing between the three time layers (1965–1982–2010). These maps and a terrestrial photograph indicate two periods of deforestation (1917–1965 and 1982–2013), whereas the forest cover was stable between 1965 and 1982. Deforestation was especially severe (with 63%) between 1982 and 2010, associated with a population increase from 77 to 153 inhabitants per square km. There is significant evidence that the elevation of the E. arborea L. tree line increased from 7 to 15 vertical meters between 1965 and 2010, in an area with decreasing anthropozoogenic pressure. Copyright © 2014 John Wiley & Sons, Ltd.

Frankl, . The effect of rainfall on the spatio-temporal variability of cropping systems and duration of the crop cover inthe Northern Ethiopian Highlands. Soil Use and Management, 29, . The effect of rainfall on the spatio-temporal variability of cropping systems and duration of the crop cover in the Northern Ethiopian Highlands. Soil Use and Management, 29,[374][375][376][377][378][379][380][381][382][383].

38This is an Open Access version of the article: Jacob, M., Annys, S., Frankl, A., De Ridder, M., Beeckman, H., Guyassa, E., Nyssen, J., 2015. Tree line dynamics in the tropical African highlands -identifying drivers and dynamics.

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Landforms and landscapes vary enormously across the Earth, from high mountains to endless plains. At a smaller scale, nature often surprises us by creating shapes which look improbable. Many physical landscapes are so immensely beautiful that they received the highest possible recognition-they hold the status of World Heritage Sites. Apart from often being immensely scenic, landscapes tell stories which not uncommonly can be traced back in time for tens of millions of years and include unique geological events such as meteorite impacts. In addition, many landscapes owe their appearance and harmony not solely to the natural forces. For centuries, and even millennia, they have been shaped by humans who have modified hillslopes, river courses and coastlines, and erected structures which often blend with the natural landforms to form inseparable entities.These landscapes are studied by geomorphology-'the science of scenery'-a part of Earth Sciences that focuses on landforms, their assemblages, surface and subsurface processes that moulded them in the past and that change them today. To show the importance of geomorphology in understanding the landscape, and to present the beauty and diversity of the geomorphological sceneries across the world, we have launched a book series World Geomorphological Landscapes. It aims to be a scientific library of monographs that present and explain physical landscapes, focusing on both representative and uniquely spectacular examples. Each book will contain details on geomorphology of a particular country or a geographically coherent region. This volume presents the impressive geomorphic legacy of Ethiopia which hosts many landscapes and landforms of global significance. Examples include the otherworldly Afar Depression with its sun-baked volcanoes, high-elevation basalt plateaus, the East African Rift valley with its splendid lakes, to name just a few. Ethiopia is also a country where geomorphology and people have remained in particularly close association since time immemorial. These relationships can be examined by referring to the past-as demonstrated by the chapter on geoarcheology of Aksum, but perhaps more importantly, with the reference to the present-day environmental problems arising from land use, soil erosion, water resources depletion and settlement growth.

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