Human impact on the environment in the Ethiopian and Eritrean highlands—a state of the art

This paper outlines the environmental history of the Tigrean Plateau (northern Ethiopia) during the Holocene, based on the available geomorphological, palynological, archaeological, and historical evidence. At present, it seems that (1) the plateau experienced a more humid climate with a denser vegetation cover during the Early Holocene; (2) Soil erosion due to clearing vegetation began in the Middle Holocene; (3) agricultural activity was intensified in the Late Holocene, as a consequence of the rise of a state; (4) demographic pressure increased from the early first millennium BC to the mid–first millennium AD, causing soil erosion; (5) environmental degradation and demographic decline occurred in the late first millennium AD; (6) the vegetation cover was regenerated in the early second millennium AD; and (7) progressive vegetation clearance started again in the second half of the second millennium AD. Cet article trace l'histoire ambiante du Plateau Tigreen dans l'Holocene en utilisant les donnees geomorphologiques, palynologiques, archeologiques et historiques. Il semble que (1) dans l'Holocene ancien le plateau etait caracterise par une phase humide avec une dense vegetation; (2) l'erosion causee par l'abbattage de la vegetation commen¸a dans l'Holocene moyen; (3) l'activite agricole s'intensifia a la fin de l'Holocene, par consequence de l'essor d'un etat; (4) la pression demographique augmenta de plus en plus du debut du premier millenaire av. J.-Ch. a la moitie du premier millenaire ap. J.-Ch.; (5) la degradation ambiante et la diminution demographique se verifierent a la fin du premier millenaire ap. J.-Ch.; (6) une regeneration de la vegetation se verifia au debut du seconde millenaire ap. J.-Ch.; et (7) l'abbatage de la vegetation recommen¸a dans la seconde moitie du seconde millenaire ap. J.-Ch.

The Environmental History of Tigray (Northern Ethiopia) in the Middle and Late Holocene: A Preliminary Outline

This paper presents a review of climate variability in the northeast Ethiopian Highlands, particularly Wollo and Tigray, during the last 10000 years (the Holocene) and an analysis of rainfall variability during the historical period. To date little work has been done on climate reconstruction in Tigray and Wollo, however, a number of ongoing studies in the area using palaeosoil analysis, archaeological techniques and lake level reconstruction will help reveal the magnitude of past climate variability in the region. On recent time scales, rainfall over Wollo is characterised by a distinctive bi-modal pattern with Belg rains in April-May preceding the main wet season Krempt, July to September, which is typical of the study region along much of the eastern escarpment. Further north over Tigray the Belg rains are less marked and the main Krempt rains dominate the seasonal pattern. Only three stations in the region, Dessie, Combolcha and Mekele, possess relatively unbroken records back to the 1950s. In all three, 1984 stands out as the driest year on record due to very low rainfall during the Krempt season, whilst 1999's Belg season was the driest on record. Although the succession of dry years between the late 1970s and late 1980s produced the driest decade in the Ethiopian Highlands this century there is no evidence for a long-term trend or change in the region's annual rainfall regime. Rainfall during the 1990s has seen a return to more humid conditions since the dry 1980s. The paper ends with a discussion of the major influences on rainfall variability over the Ethiopian Highlands: the El Nino-Southern Oscillation - El Nino events tend to be associated with lower than average rainfall; Atlantic, Indian and Pacific Ocean sea surface temperatures play a varying role in different seasons; the strength of the Indian Summer Monsoon; and the frequency of several tropical depressions over the Southwest Indian Ocean. SINET: Ethiopian Journal of Science Vol. 23, No. 2 (December 2000), pp. 139-161 Key words/phrases: Climate, El Nino, Ethiopian Highlands, Holocene, rainfall variability

/pdf/some-aspects-of-climate-variability-in-the-north-east-p2pk90jkl5.pdf

Some aspects of climate variability in the north east Ethiopian highlands - Wollo and Tigray

Small-scale aerial photographs and high-resolution satellite images, available for Ethiopia since the second half of the twentieth century as for most countries, allow only the length of gullies to be determined. Understanding the development of gully volumes therefore requires that empirical relations between gully volume (V) and length (L) are established in the field. So far, such V–L relations have been proposed for a limited number of gullies/environments and were especially developed for ephemeral gullies. In this study, V–L relations were established for permanent gullies in northern Ethiopia, having a total length of 152 km. In order to take the regional variability in environmental characteristics into account, factors that control gully cross-sectional morphology were studied from 811 cross-sections. This indicated that the lithology and the presence of check dams or low-active channels were the most important controls of gully cross-sectional shape and size. Cross-sectional size could be fairly well predicted by their drainage area. The V–L relation for the complete dataset was V = 0 · 562 L 1·381 (n = 33, r2 = 0 · 94, with 34 · 9% of the network having check dams and/or being low-active). Producing such relations for the different lithologies and percentages of the gully network having check dams and/or being low-active allows historical gully development from historical remote sensing data to be assessed. In addition, gully volume was also related to its catchments area (A) and catchment slope gradient (Sc). This study demonstrates that V–L and V–A × Sc relations can be very suitable for planners to assess gully volume, but that the establishment of such relations is necessarily region-specific. Copyright © 2013 John Wiley & Sons, Ltd.

https://biblio.ugent.be/publication/3118104/file/6784576.pdf

Factors controlling the morphology and volume (V)–length (L) relations of permanent gullies in the northern Ethiopian Highlands

Age and backfill/overfill stratigraphy of two tufa dams, Tigray Highlands, Ethiopia: Evidence for Late Pleistocene and Holocene wet conditions

The Mai Maikden sedimentary sequence : a reference point for the environmental evolution of the Highlands of Northern Ethiopia

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The Mai Maikden sedimentary sequence : a reference point for the environmental evolution of the Highlands of Northern Ethiopia