Purpose The Ethiopian highlands are a fragile environment, characterized by steep slopes, intense rainfall, a sparse vegetation cover and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100-10,000 km²)are not fully understood. Therefore, this study aims to provide a better of sediment export processes and the importance of flash flood events in semi-arid tropical catchments. 2Methods Measuring campaigns were conducted in 10 subcatchments of the Geba, a tributary of the Tekeze, representative of the northern Ethiopian highlands. During 2 to 4 rainy seasons, the rivers were sampled for their suspended sediment concentration (SSC) and runoff discharge.Results and discussion Variations in SSC and sediment grain-size distribution indicate changes in sediment supply during the rainy season, due to the depletion of readily available sediments and the development of a vegetation cover.Also during flood events, changes in sediment supply are observed. Sediment yields (i.e. 497-6,543 t km -2 yr -1 ) are higher than suggested by previous studies and correlate with rainfall depth. The majority of sediment export occurs during a few short but intense flash floods. No clear effect of implemented soil and water conservation measures could be detected in the sediment yields of the catchments.Conclusions Sediment export rates in the Ethiopian highlands are high, are characterized by important changes in sediment supply and are mainly controlled by the occurrence and magnitude of flash flood events. Mitigation measures to reduce sediment yield at the catchment scale should therefore not only focus on the reduction of hillslope erosion rates, but also on the magnitude of these floods.

This Special Issue of Land Degradation and Development addresses the past and the future of land management in Africa with a focus on northern Ethiopia. How did the status of soils and forests change over the last century? How does this impact people's livelihoods? In the late 19th century, gullies were already present in northern Ethiopia, though they had become stabilised by 1935. In the 1960s, a strong gully channel incision phase started, whereas since ca. 2000, gully erosion rates are again decreasing, which corresponds to increased conservation activities and improved vegetation cover. As a result, total cereal production in Ethiopia is now higher than ever, and also, food production per capita in 2005–2010 was 160% of that in 1985–1990. There is now a strong tendency to increase flower and vegetable exports, as well as a booming export of the mild narcotic khat, which is a high water consumer. International land deals did not bring improvements to the livelihood of the local people. Copyright © 2015 John Wiley & Sons, Ltd.

Water availability has for long been a critical issue in many developing countries. Despite its enormous potential of water resources, Ethiopia is suffering from a lack of water availability and threatened by the consequences of climate change. Well considered planning to develop these resources is crucial. However, very few observational runoff data exist for this type of environments. Especially runoff data for catchments at the intermediate scale (100 -10,000 km²) are lacking. This study assesses the runoff from 10 mediumsized catchments in the Geba river basin, a subcatchment of the Nile in the semi-arid degraded northern Ethiopian highlands. Flow depth records were automatically obtained every 10 minutes during the rainy seasons (July -September) of 2004-2007 and converted to continuous runoff discharge records.Cumulative annual runoff depths (46 -395 mm) are mainly correlated with rainfall depth. Estimated runoff coefficients (9 -47%) and are negatively correlated with the areal fraction of limestone outcrops in the catchments, indicating runoff transmission losses.Throughout the rainy season, increases in runoff depth and runoff coefficient were observed, which is partly attributed to an increase in baseflow throughout the season. The majority of the runoff occurs during flash floods, i.e. relatively short runoff events with often very high peak discharges. Characteristics of these floods 2 are discussed with some examples, including an exceptionally large flood. Taking into account the difficult conditions for river discharge measurements in a country like Ethiopia, this study provides one of the most comprehensive analyses so far of the magnitude and dynamics of river discharges in Ethiopia.

No abstract

Farmers in Northern Ethiopia integrate legumes in their cropping systems to improve soil fertility. However, biological nitrogen fixation (BNF) potentials of different legumes and their mineral nitrogen (N) and phosphorus (P) demands for optimum BNF and yields are less studied. This study aimed to generate the necessary knowledge to enable development of informed nutrient management recommendations, guide governmental public policy and assist farmer decision making. The experiment was conducted at farmers’ fields with four N levels, three P levels, and three replications. Nodule number and dry biomass per plant were assessed. Nitrogen difference method was used to estimate the amount of fixed N by assuming legume BNF was responsible for differences in plant N and soil mineral N measured between legume treatments and wheat. The result revealed that the highest grain yields of faba bean (2531 kg ha−1), field pea (2493 kg ha−1) and dekeko (1694 kg ha−1) were recorded with the combined application of 20 kg N ha−1 and 20 kg P ha−1. Faba bean, field pea and dekeko also fixed 97, 38 and 49 kg N ha−1, respectively, with the combined application of 20 kg N ha−1 and 20 kg P ha−1; however, lentil fixed 20 kg ha−1 with the combined application of 10 kg N ha−1 and 10 kg P ha−1. The average BNF of legumes in the average of all N and P interaction rates were 67, 23, 32 and 16 kg N ha−1 for faba bean, field pea, dekeko and lentil, respectively. Moreover, faba bean, field pea, dekeko and lentil accumulated a surplus soil N of 37, 21, 26 and 13 kg ha−1, respectively, over the wheat plot. The application of 20 kg N ha−1 and 20 kg P ha−1 levels alone and combined significantly (p < 0.05) increased the nodulation, BNF and yield of legumes; however, 46 kg N ha-1 significantly decreased BNF. This indicated that the combination of 20 kg N ha−1 and 20 kg P ha−1 levels is what mineral fertilizer demands to optimize the BNF and yield of legumes. The results of this study can lead to the development of policy and farmer guidelines, as intensification of the use of legumes supplied with starter N and P fertilizers in Northern Ethiopian cropping systems has the multiple benefits of enhancing inputs of fixed N, improving the soil N status for following crops, and becoming a sustainable option for sustainable soil fertility management practice.

No abstract

No abstract

Despite many studies on land degradation in the Highlands of Northern Ethiopia, quantitative information regarding long-term changes in land use/cover (LUC) is rare. Hence, this study aims to investigate the LUC changes in the Geba catchment (5142 km 2), Northern Ethiopia, over 80 years (1935-2014). Aerial photographs (APs) of the 1930s and Google Earth (GE) images (2014) were used. The point-count technique was utilized by overlaying a grid on APs and GE images. The occurrence of cropland, forest, grassland, shrubland, bare land, built-up areas and water body was counted to compute their fractions. A multivariate adaptive regression spline was applied to identify the explanatory factors of LUC and to create fractional maps of LUC. The results indicate significant changes of most types, except for forest and cropland. In the 1930s, shrubland (48%) was dominant, followed by cropland (39%). The fraction of cropland in 2014 (42%) remained approximately the same as in the 1930s, while shrubland significantly dropped to 37%. Forests shrank further from a meagre 6.3% in the 1930s to 2.3% in 2014. High overall accuracies (93% and 83%) and strong Kappa coefficients (89% and 72%) for point counts and fractional maps respectively indicate the validity of the techniques used for LUC mapping.