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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 6
Hydrol. Earth Syst. Sci., 15, 1979–1989, 2011
https://doi.org/10.5194/hess-15-1979-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Climate, weather and hydrology of East African Highlands

Hydrol. Earth Syst. Sci., 15, 1979–1989, 2011
https://doi.org/10.5194/hess-15-1979-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Jun 2011

Research article | 27 Jun 2011

Changes in land cover, rainfall and stream flow in Upper Gilgel Abbay catchment, Blue Nile basin – Ethiopia

T. H. M. Rientjes1, A. T. Haile1, E. Kebede2, C. M. M. Mannaerts1, E. Habib3, and T. S. Steenhuis4 T. H. M. Rientjes et al.
  • 1Department of Water Resources Faculty of Geo-information Science and Earth Observation (ITC) University of Twente, P.O. Box 6, 7500AA, Enschede, The Netherlands
  • 2SNNPR Water Resources Development, Bureau Awassa, P.O. Box 925, Awassa, Ethiopia
  • 3Department of Civil Engineering, University of Louisiana at Lafayette, Lafayette, LA 70504, USA
  • 4Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA

Abstract. In this study we evaluated changes in land cover and rainfall in the Upper Gilgel Abbay catchment in the Upper Blue Nile basin and how changes affected stream flow in terms of annual flow, high flows and low flows. Land cover change assessment was through classification analysis of remote sensing based land cover data while assessments on rainfall and stream flow data are by statistical analysis. Results of the supervised land cover classification analysis indicated that 50.9 % and 16.7 % of the catchment area was covered by forest in 1973 and 2001, respectively. This significant decrease in forest cover is mainly due to expansion of agricultural land.

By use of a change detection procedure, three periods were identified for which changes in rainfall and stream flow were analyzed. Rainfall was analyzed at monthly base by use of the Mann-Kendall test statistic and results indicated a statistically significant, decreasing trend for most months of the year. However, for the wet season months of June, July and August rainfall has increased. In the period 1973–2005, the annual flow of the catchment decreased by 12.1 %. Low flow and high flow at daily base were analyzed by a low flow and a high flow index that is based on a 95 % and 5 % exceedance probability. Results of the low flow index indicated decreases of 18.1 % and 66.6 % for the periods 1982–2000 and 2001–2005 respectively. Results of high flows indicated an increase of 7.6 % and 46.6 % for the same periods. In this study it is concluded that over the period 1973–2005 stream flow has changed in the Gilgel Abbay catchment by changes in land cover and changes in rainfall.

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