Comprehensive assessment of soil erosion risk for better land use planning in river basins: Case study of the Upper Blue Nile River.
In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5tha-1yr-1and a gross soil loss of ca. 473Mtyr-1, of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score=1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (>30tha-1yr-1) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (>15tha-1yr-1), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region.
International Platform for Dryland Research and Education, Tottori University, Tottori 680-0001, Japan; Arid Land Research Center, Tottori University, Tottori 680-0001, Japan. Electronic address: nigussie_haregeweyn@alrc.tottori-u.ac.jp.
Nigussie
N
Haregeweyn
International Platform for Dryland Research and Education, Tottori University, Tottori 680-0001, Japan; Arid Land Research Center, Tottori University, Tottori 680-0001, Japan.
Atsushi
A
Tsunekawa
Department of Earth and Environmental Sciences, Division of Geography and Tourism, KU Leuven, Celestijnenlaan 200 E, B-3001 Heverlee, Belgium.
Jean
J
Poesen
Institute for Soil, Climate and Water, Agricultural Research Council, South Africa.
Mitsuru
M
Tsubo
Department of Natural Resources Management, Bahir Dar University, Bahir Dar, Ethiopia.
Derege Tsegaye
DT
Meshesha
Department of Land Resources Management and Environmental Protection, Mekelle University, Mekelle, Ethiopia.
Ayele Almaw
AA
Fenta
Geography Department, Gent University, Gent, Belgium.
Jan
J
Nyssen
Department of Natural Resources Management, Bahir Dar University, Bahir Dar, Ethiopia.
Enyew
E
Adgo
Drought-prone; Grand Ethiopian renaissance dam; Gross soil loss; Gully erosion; Sediment yield; Soil and water conservation