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Now showing items 1 - 7 of 7

  • Over one century of rainfall and temperature observations in Addis Ababa, Ethiopia

    Conway, D   Mould, C   Bewket, W  

    A detailed historical reconstruction and analysis is presented of the longest record of climate observations for Ethiopia, from 1898 to 2002 in Addis Ababa. Prior to 1951 the record comprises rainfall and minimum and maximum temperatures recorded in different locations by different observers. The rainfall series is complete except for 1899 and 1900, but the temperature series are very incomplete. Using documentary evidence, we attempt as far as is possible to establish the origins of all the pre-1951 observations. Rainfall observations originate from at least six different sites. After establishment of an Ethiopian meteorological department in 1951 the records are complete and, to our understanding, originate from the same location, the Addis Ababa Observatory (AAO). A revised rainfall series for 1898-1950 is derived using observations from sites with the longest records. The minimum and maximum temperature records show evidence of statistically significant inhomogeneities. Homogeneity tests on the full rainfall record (the revised series plus AAO) show it is reliable, with evidence of minor but not statistically significant breaks in the record before establishment of the AAO. Some, but not all, breaks can be accounted for using the historical information. Analysis of the records shows increasing trends in annual minimum and maximum temperatures from 1951 to 2002 (0.4 degreesC/decade and 0.2 degreesC/decade, respectively). There is little trend in rainfall from 1901-50, 1951-2002 and 1901-2002, dry years do not correspond with known drought years elsewhere in Ethiopia, and interannual variability is poorly correlated with another long rainfall series in Ethiopia (Gore), Blue Nile river flows and the southern oscillation index. This suggests strongly that the record for Addis Ababa should not be used as a proxy for conditions in Ethiopia, particularly the more drought-prone areas to the north and east. We conclude that the temperature series are suspect but that the full rainfall record is useful for analysis of long-term rainfall conditions in Addis Ababa. (C) Copyright 2004 Royal Meteorological Society.
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  • Dynamics in land cover and its effect on stream flow in the Chemoga watershed, Blue Nile basin, Ethiopia

    Bewket, W   Sterk, G  

    The objective of this study was to analyse changes in stream flow patterns with reference to dynamics in land cover/use in a typical watershed, the Chemoga, in northwestern highland Ethiopia. The results show that, between 1960 and 1999, total annual stream flow decreased at a rate of 1(.)7 mm year(-1), whereas the annual rainfall decreased only at a rate of 0(.)29 mm year(-1). The decrease in the stream flow was more pronounced during the dry season (October to May), for which a statistically significant decline (0(.)6 mm year(-1)) was observed while the corresponding rainfall showed no discernible trend. The wet season (June to September) rainfall and stream flow did not show any trends. Extreme low flows analysed at monthly and daily time steps reconfirmed that low flows declined with time, the changes being highly significant statistically. Between 1960 and 1999, the monthly rainfall and stream flow amounts of February (month of lowest long-term mean flow) declined by 55% and 94% respectively. Similarly, minimum daily flows recorded during the three driest months (December to February) showed statistically highly significant declines over the same period. It declined from 0(.)6 m(3) s(-1) to 0(.)2 m(3) s(-1) in December, from 0(.)4 m(3) s(-1) to 0(.)1 m(3) s(-1) in January and from 0(.)4 m(3) s(-1) to 0(.)02 m(3) s(-1) in February (1.0 m(3) s(-1) = 0.24 mm day(-1) in the Chemoga watershed). In contrast. extreme high flows analysed at monthly (for August) and daily (July to September) time steps did not reveal discernible trends. The observed adverse changes in the stream flow have partly resulted from changes in land cover/use and/or degradation of the watershed that involved destruction of natural vegetative covers, expansion of croplands, overgrazing and increased area under eucalypt plantations. The other contributory factor has been the increased dry-season water abstraction to be expected from the increased human and livestock populations in the area. Given the significance of the stream flow as the only source of water to the local people, a set of measures aimed at reducing magnitudes of surface runoff generation and increasing groundwater recharge are required to sustain the water resource and maintain a balanced dry-season flow in the watershed. Generally, an integrated watershed management approach, whereby the whole of the watershed can be holistically viewed and managed, would be desirable. Copyright (C) 2004 John Wiley Sons, Ltd.
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  • Household level tree planting and its implications for environmental management in the northwestern highlands of Ethiopia: A case study in the Chemoga watershed, Blue Nile Basin

    Bewket, W  

    The unsustainable exploitation and destruction of forests is a serious environmental concern in the developing countries of Africa. One of its main driving forces is the growing population causing a growing demand for fuelwood. In Ethiopia, as in many developing countries, there is a heavy dependence on and a growing demand for fuelwood. This dependence has been contributing to a widescale deforestation, as stated in various reports. Contrary to these reports, a study in the Chemoga watershed found a slightly increased forest cover during the past four decades, which was ascribed to households' tree planting practices. The objective of this study was to examine household level tree planting activities in reference to biofuel consumption patterns in four sample villages in the watershed. The results indicate that fuelwood and cattle dung accounted for nearly 100 per cent of the domestic energy consumption, with cattle dung contributing 34 per cent of the total. Fuelwood and dung combined, per capita biofuel consumption was estimated at 511 kg yr(-1), but with variations between the villages and socio-economic groups. Supply appears to have influenced the quantity of biofuels used. The scarcity of wood for fuel and other uses has forced households to plant trees. This has contributed to the increased forest cover of the watershed at the present as compared to that four decades ago. Number of trees planted showed variation between the villages and socio-economic groups, which is attributable to physical and human factors. In promoting tree planting, agroforesters and environmental management planners should therefore take into account local level biophysical and socio-economic realities. This agroforestry practice is a good short-term solution to the problem of fuelwood shortage, and also has many positive implications for environmental management and agricultural production. Thus, it has to be encouraged. Spatially aggregated, local level agroforestry practices contribute positively towards global ecosystem health. Copyright (C) 2003 John Wiley Sons, Ltd.
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  • Assessment of soil erosion in cultivated fields using a survey methodology for rills in the Chemoga watershed, Ethiopia

    Bewket, W   Sterk, G  

    Soil erosion by water is recognized to be a critical economic problem in highland Ethiopia. However, nearly all the available information about its severity and economic costs are extrapolated from plot and micro-watershed level studies which are too few in number to represent the diverse environments of the country. Moreover, plot and watershed level studies do not show actual soil losses from cultivated fields, while understanding the magnitude of soil loss at the field scale is important for practical conservation planning. This Paper reports results of field-scale soil erosion assessment that employed a survey methodology for rills and was conducted over two wet seasons (the years 2000 and 2001) at two sites, Kechemo and Erene, located in the upstream and downstream reaches of the Chemoga watershed, northwestern highland Ethiopia. The two wet seasons average rill erosion magnitudes were 13.5 Mg ha(-1) in the Kechemo and 61 Mg ha(-1) in the Erene. Assuming that interrill erosion contributes 30%, actual soil losses were around 18 Mg ha(-1) in the Kechemo and 79 Mg ha(-1) in the. Erene. These estimates, which are well in agreement with results obtained by measurements in a nearby experimental micro-watershed, reveal that soil erosion is a threat to agricultural production in the study area and conservation measures are needed.. Soil erosion showed significant spatial (between and within the two sites) and temporal variations. Hence, soil and water conservation (SWC) measures that fit well into local-scale circumstances will be realistic and acceptable to the farmers. Additionally, the problem of soil erosion should be tackled in the watershed context, because there is a strong physical interdependence between upstream and downstream areas. Finally, the study confirms that the rill survey approach gives good semi-quantitative information on soil erosion in real life situations of diverse fanning and land use practices in a fast and inexpensive way; and it is commendable for practical conservation-oriented soil erosion assessment purposes. (C) 2003 Elsevier Science B.V. All rights reserved.
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  • Effects of agroecological land use succession on soil properties in Chemoga watershed, Blue Nile basin, Ethiopia

    Bewket, W   Stroosnijder, L  

    This study appraises the effects of land use on soil properties in a typical watershed in the northwestern highland of Ethiopia. Soil samples were collected from major land use types in the watershed: natural forests, cultivated lands, grazing lands and Eucaliplus plantations. The natural forests served as a control against which to assess changes in soil properties resulting from the establishment of the other land use types. Samples were taken at two depths (0-15 and 15-30 cm) in the upstream and downstream areas of the watershed and analyzed for a range of soil properties. The soils in the cultivated fields, grazing lands and Eucalyptus plantations showed significantly higher sand content, but lower Ca2+ and Mg2+ contents and cation exchange capacity (CEC) compared to soils under natural forests. Eucalyptus soils had a statistically significant higher bulk density (BD) than soils under the other three land use types. The forest and Eucalyptus soils also differed significantly from each other in their soil organic matter (SOM) and total N contents. A significant difference in available P among soils of the four land use types was caused by the difference between cultivated and Eucalyptus soils. In contrast, the distribution of soil silt fraction Na+, K+ and pH values did not differ among the four land use types. Significant differences in many of the soil properties were also observed between soils in the two sampled villages. The study underscores the need for policies and strategies for sustainable land use that will attune objectives of economic development to environmental management at the regional and local levels. (C) 2002 Elsevier Science B.V All rights reserved.
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  • Land cover dynamics since the 1950s in Chemoga Watershed, Blue Nile Basin, Ethiopia

    Bewket, W  

    This study evaluated changes in land cover in the Chemoga watershed, headwater to the Blue Nile. Two sets of aerial photographs (1957 and 1982) and a multispectral Spot image (1998) were used as inputs to produce 3 GIS-based land cover maps of the area. The results show that during the last 41 years, forest cover increased at a rate of about 11 ha per annum in the 36,400-ha watershed. Woodlands and shrublands decreased between 1957 and 1982 but increased between 1982 and 1998, approximately to their previous levels. Farmland and settled areas gained from the other cover types (13% increase) in the first period but lost around 586 ha (2% decrease) in the second. Grassland and degraded land decreased, accounting for 4.8% of the total area of the watershed in 1982 and 3.5% in 1998, as against 9.6% in 1957. Riverine trees suffered the greatest destruction, shrinking by 79% over the 4 decades; much of this decline was due to cultivation. Marshlands increased in the first period and decreased in the second. A new pond emerged amid the marshlands between 1982 and 1998. Population growth and the associated demand for land and trees was the major driving force behind the changes. This study shows that the deforestation trend was reduced and even partly reversed in the area because local people planted trees as a source of fuel and income. This trend ought to be encouraged through appropriate interventions-in particular by promoting planting of local species rather than eucalyptus-to increase not only economic but also ecological benefits. Indeed, the current state of land cover and its dynamics have environmental implications at the local scale and beyond. Hence, environmental management for sustainable development requires interregional and international cooperation.
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  • Farmers' participation in soil and water conservation activities in the Chemoga watershed, Blue Nile basin, Ethiopia

    Bewket, W   Sterk, G  

    Soil erosion by water constitutes a threat to the maintenance of the subsistence living of the Ethiopian rural population. Past efforts at Soil and Water Conservation (SWC) did not bring about significant results, mainly because of the top-down approach pursued. Uprooting this past oversight and instating a participatory approach has since then been strongly recommended as the correct strategy. This paper analyses the extent of farmers' participation in current SWC activities in the Chemoga watershed, East Gojjam Zone, Amhara Regional State. Formal household survey, informal and focus group discussions and field observation were used to generate the data. The results indicate that the majority of the farmers participated in the SWC against their will. The most important factor discouraging them from participating freely was the perceived ineffectiveness of the structures under construction. Awareness about soil erosion as a problem, labour shortage and land tenure insecurity were found to be less important in providing an explanation for the disinterest shown by most of the farmers towards the SWC activities. Therefore, the important factors that need immediate consideration for SWC efforts in the study area or the region at large are: (1) SWC structures have to be carefully designed and constructed taking into account ground realities, and (2) participation of the farmers has to be through their own conviction regarding the effectiveness and efficiency of the technologies. Alternative SWC technologies will have to be considered in this regard. Copyright, (C) 2002 John Wiley Sons, Ltd.
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